Method To Take Control of Cell Modem



  • Is there a way to directly take control of the cell modem and talk to it directly with a raw serial interrupt driver (machine.UART)? In other words I do not want to use the LTE module other than possibly initializing the cell modem. I want to write all the modem interaction including the LTE.send_at_cmd() in 100% MicroPython using AT commands. I'll handle all the modem responses, timeouts, error checking, etc. No calls to the LTE module desired.

    Why would I want to do such a thing (call me crazy)?

    I want to try using the built-in Sequans "Specific HTTP Commands".

    Maybe this would improve the integrity of the GPy.

    I currently have a program working in production using Pycom MicroPython V1.20.0.rc13 on many units. When I try to run the same program on a newly purchased GPy running Pycom MicroPython 1.20.2.r3, the program crashes (20 sec watchdog timeout) when I do an AT command ('AT+CEREG?') after disconnecting from a successful transmission. How do I troubleshoot such a crash?

    Modem commands have always interfered with multi-threading and interrupt servicing. Maybe using just the MicroPython serial interrupt drivers would allow more smooth multi-threading and interrupt servicing. I could also have complete control over modem interaction, timeouts, retries, etc. without affecting the other tasks running on the system. Sending commands to a cell modem should not interfere with the servicing of an interrupt or the switching of threads in MicroPython.

    Looking at the C code for the LTE module shows a significant amount of complexity. Let's open up the cell communication software in Python so everyone can see and make improvements and changes. Let's create high level commands in Python that make cell communication reliable and transparent to the rest of the system.

    I've built embedded cell modem based systems using just AT commands that worked great. It shouldn't be that complicated.

    Another possibility is to run the ESP32 MicroPython on the GPy and bypass Pycom's implementation. Has anyone tried this before?



  • @tlanier I really like the sound of what your doing here. I've been struggling with Pycom LTE module for months now. Really don't like the way it blocks other threads and randomly locks up for no apparent reason. Are you possibly in a position to share a complete "Hello LTE World" example. I'm sure I wouldn't be the only one around here who would be very interested. Hopefully someone from Pycom might also take an interest and finally admit they need to revise their code.



  • We now have our program running completely independent of the LTE module. 26 units have been running for multiple days with no crashes. I now think we have found a reliable solution. The Sequans modem AT socket commands are used to do the HTTP posts. We reliably receive 90K files and transmit 1-5K of data with no issues. Pycom MicroPython V1.20.0.rc13 is the OS version we are using.

    Currently we are using whatever version of the modem firmware (41065, 43818, and 47510 have been seen) that comes with the GPy. The version of the OS we are using has the ability to "downgrade" the modem firmware to 41065 if we decide it is needed. Some newer versions of the OS do not have this ability.

    One note of importance is we did discover that in our case the default stack size was marginal when receiving large files. Yes, I did go back and check the old program and verified that the stack issue was not the cause of the original crash problems.

    #####################################################################
    #                          Initialize Tasks
    #####################################################################
    def init_tasks():
        n = 8192    # 4096 is marginal
        _thread.stack_size(n)
        log("initializing tasks with stack size: {}".format(n))
        
        _thread.start_new_thread(com.com_task, ())
        _thread.start_new_thread(cycle.cycle_task, ())
    


  • I've now converted my code to use the Sequans modem socket commands in command mode (not on-line mode). I first tried to use the on-line mode, but ran into issues (no good way I could find to prevent overrunning tx buffer). This code resolves the 1500 byte limitation I ran into using the HTTP modem commands. There's still some cleanup to do to make the code more robust; however, it is working with large transmit and receive data blocks now.

    During development while I had coding errors and the program would terminate abnormally, I did put the modem in a mode that I couldn't recover from without power cycling the GPy. The modem would not response to AT commands, Trying to do lte = LTE() would generate the following error (OSError: Couldn't connect to Modem (modem_state=disconnected)). Doing machine.reset() would not correct the problem.

    Link to discussion of similar problem on Github

    Hopefully whatever I did to cause the problem will not occur in debugged code. There needs to be a true hardware reset of the modem. It seems that a GPIO pin should be tied to a physical reset line going to the modem that we could pulse if needed. I'm also of the opinion that the watchdog timer in the GPy should have been a hardware circuit not dependent on software to work.

    So far I have not seen any unexplained crashes while running the code.

    This code has been added to my modem.py module.

    #####################################################################
    #                       Socket Close          
    #####################################################################
    def socket_close():
        # socket close
        # connID = 1 --> socket connection identifier
        a = at('AT+SQNSH=1', 'OK')
        if len(a) == 0:
            log("error closing connection")
            return
    
    
    #####################################################################
    #                       Socket Connect          
    #####################################################################
    def socket_connect(ip, port, timeout_secs=10):
        # returns: True if connection successful
        log("connecting to ip - {0}, port - {1}".format(ip, port))
    
        # make sure socket is closed
        socket_close()
    
        # socket configuration
        # connID = 1 --> socket connection identifier
        # cid = 1 --> PDP context identifier
        # pktSz = 1500 --> packet size
        # maxTo = 10 --> exchange timeout in secs
        # connTo = 600 --> connection timeout in msecs
        # txTo = 3 --> data sending timeout in hundreds of msecs
        # a = at('AT+SQNSCFG=1,1,1500,10,600,3', 'OK')
        a = at('AT+SQNSCFG=1,1,1500,{0},600,3'.format(timeout_secs), 'OK')
        if len(a) == 0:
            log("error connecting")
            return False
        
        # socket extended configuration
        # connID = 1 --> socket connection identifier
        # srMode = 1 --> SQNSRING URC data amount mode
        # recvDataMode = 1 --> data in hex
        # keepalive = 0 --> unused
        # listenAutoRsp = 0 --> deactivated
        # sendDataMode = 1 --> data in hex
        a = at('AT+SQNSCFGEXT=1,1,1,0,0,1', 'OK')
        if len(a) == 0:
            log("error connecting")
            return False
    
        # socket dial
        # connID = 1 --> socket connection identifier
        # txProt = 0 --> TCP protocol
        # rPort = <port> --> remote host port to contact
        # IPaddr = <ip> --> address of remote host
        # closureType = 0 --> local host closes immediately when remote host has closed
        # lPort = 0 --> UDP port (not used)
        # connMode = 1 --> command mode connection
        # acceptAnyRemote = 0 --> disabled 
        a = at('AT+SQNSD=1,0,{0},"{1}",0,0,1,0'.format(port,ip), 'OK')
        if len(a) == 0:
            log("error connecting")
            return False
    
        log("** connection successful **")
        return True
        
    
    #####################################################################
    #                       Socket Info         
    #####################################################################
    def socket_info():
        # modem response: ['+SQNSI: 1,0,0,0,0', 'OK']
        # connId: 1
        # sent: total bytes sent
        # received: total bytes received
        # buff_in: total bytes not yet read (buffered)
        # ack_waiting: total bytes sent but not yet acknowledged
        a = at('AT+SQNSI=1')
    
    
    #####################################################################
    #                       Socket Receive Data         
    #####################################################################
    def socket_rx():
        # receives up to 1500 bytes maximum
        log("check for rx data")
        a = at('AT+SQNSRECV=1,1500')
        # no data ready --> modem response: ['+CME ERROR: operation not supported']
        # data ready --> modem response: ['+SQNSRECV: 1,3', '010203', 'OK']
        b = b''
        for i in range(len(a)):
            if a[i].startswith('+SQNSRECV:'):
                # next line is the data
                b = unhexlify(a[i+1])
    
        log("rx {0} bytes".format(len(b)))
        return b
    
    
    #####################################################################
    #                       Socket Status         
    #####################################################################
    def socket_status():
        # modem response: ['+SQNSS: 1,0', '+SQNSS: 2,0', '+SQNSS: 3,0', '+SQNSS: 4,0', '+SQNSS: 5,0', '+SQNSS: 6,0', 'OK']
        # connID
        # state: 
        #   0-socket closed
        #   1-socket with active data transfer connection
        #   2-socket suspended
        #   3-socket suspended with pending data
        #   4-socket listening
        #   5-socket with incoming connection
        #   6-socket in opening process
        a = at('AT+SQNSS?')
        return a
    
    
    #####################################################################
    #                       Socket Transmit Data         
    #####################################################################
    def socket_tx(tx, n=0):
        # transmits up to 1500 bytes maximum
        # returns: True if successful
        if n == 0:
            n = len(tx)
        
        log("tx {0} bytes".format(n))
        a = at('AT+SQNSSENDEXT=1,{0}'.format(n), '> ')
        hex = hexlify(tx)
        uart.write(hex)
        a = at_response('OK')
        if len(a) == 0:
            log("error transmitting data")
            return False
    
        return True
    

    This code is in my http.py module.

    import modem
    import sys
    import ubinascii
    import uos
    import ustruct
    import util
    from util import log
    from utime import sleep_ms, ticks_ms, ticks_diff
    
    BUFFER_SIZE = const(1500)
    CR = const(0x0d)
    LF = const(0x0a)
    MAX_HEADER_SIZE = const(128)
    MAX_TX_SIZE = const(1500)
    HTTP_TIMEOUT_MSECS = const(15000)
    # HTTP_TIMEOUT_MSECS = const(300000)  # TESTING
    
    http_error = False      # HTTP communication error: True/False
    http_size = 0           # HTTP POST message size
    rx_cnt = 0              # no. bytes in rx_data buffer
    rx_data = b''           # rx data buffer
    rx_pt = 0               # pointer into rx data buffer
    tx_cnt = 0              # no. bytes in tx_data buffer
    tx_data = bytearray(MAX_TX_SIZE)    # tx data buffer
    tx_flag = False         # controls tx_byte 
    
    #####################################################################
    #                       Close HTTP Socket
    #####################################################################
    def close_http():
        modem.socket_close()
    
    
    #####################################################################
    #                       Open HTTP Socket
    #####################################################################
    def open_http(host_ip, host_port):
        global http_error, rx_cnt, rx_data, rx_pt, tx_cnt
        
        http_error = False
        rx_cnt = 0
        rx_data = b''
        rx_pt = 0
        tx_cnt = 0
    
        r = modem.socket_connect(host_ip, host_port)
        if r == False:
            log("TCP socket connect error")
            http_error = True
    
    
    #####################################################################
    #                    Receive BLOCK From Response
    #####################################################################
    def rx_block(cnt):
        b = bytearray(cnt)
        i = 0
        while i < cnt:
            b[i] = rx_byte()
            i = i + 1
    
        return b
    
    
    #####################################################################
    #                    Receive BYTE From Response
    #####################################################################
    def rx_byte():
        global http_error, http_size, rx_cnt, rx_data, rx_pt
    
        t0 = ticks_ms()
    
        while rx_cnt == 0:
            rx_data = modem.socket_rx()
            rx_cnt = len(rx_data)
            rx_pt = 0
            if rx_cnt > 0:
                break
    
            t1 = ticks_ms()
            tx = ticks_diff(t1, t0)
            if (tx > HTTP_TIMEOUT_MSECS):
                http_error = True
                return 0
    
            sleep_ms(200)
    
        b = rx_data[rx_pt]
        rx_cnt = rx_cnt - 1
        rx_pt = rx_pt + 1
        http_size = http_size - 1
    
        # print("rx byte: {0}".format(hex(b)))
        return b
    
    
    #####################################################################
    #                    Receive DWORD From Response
    #####################################################################
    def rx_dword():
        dw1 = rx_byte()
        dw2 = rx_byte()
        dw3 = rx_byte()
        dw4 = rx_byte()
    
        return (dw1 + (dw2<<8) + (dw3<<16) + (dw4<<24))
    
    
    #####################################################################
    #                    Receive One HTTP Header
    #####################################################################
    def rx_http_header():
        # returns header string
        global http_error
    
        n = 0
        header = bytearray(MAX_HEADER_SIZE)
        s = ""
    
        while True:
            b = rx_byte()
            # print("byte = {0}".format(b))
            if http_error:
                return ""
    
            if b == CR:
                continue
    
            if b == LF:
                break
    
            header[n] = b
            n = n + 1
    
            if n >= MAX_HEADER_SIZE-1:
                http_error = True
                return ""
    
        if n > 0:
            # print("n = {0}, header = {1}".format(n,header))
            s = header[0:n].decode('utf-8')
        
        return s
    
            
    #####################################################################
    #                    Receive HTTP Headers
    #
    # HTTP/1.1 200 OK
    # <headers>
    # Content-Length: nnn
    # <headers>
    # <crlf>
    #
    # Updates: http_size, http_error
    #####################################################################
    def rx_http_headers():
        global http_error, http_size
    
        headers = []      # array of header lines
        http_size = 0
    
        while True:
            s = rx_http_header()
            log("length = {0}, header = {1}".format(len(s), s))
            if http_error:
                return headers
    
            if s == "":
                break
    
            headers.append(s)
     
        if len(headers) < 2:
            http_error = True
            return headers
        
        a = headers[0].split(' ')
        if (a[1] != "200") or (a[2]) != "OK":
            http_error = True
            return headers
    
        for s in headers:
            if s.startswith("Content-Length:"):
                a = s.split(' ')
                http_size = int(a[1])
    
        return headers
    
    
    #####################################################################
    #                    Receive String From Response
    #####################################################################
    def rx_string(max_len):
        rx = bytearray(max_len)
        i = 0
        while i < max_len:
            b = rx_byte()
            if b == 0:
                break
    
            rx[i] = b
            i = i + 1
    
        if i == 0:
            return ""
    
        s = rx[0:i].decode('utf-8')
    
        return s
    
    
    #####################################################################
    #                    Receive WORD From Response
    #####################################################################
    def rx_word():
        dw1 = rx_byte()
        dw2 = rx_byte()
    
        return (dw1 + (dw2<<8))
    
    
    #####################################################################
    #                       Transmit Block
    #####################################################################
    def tx_block(b):
        for x in b:
            tx_byte(x)
    
    
    #####################################################################
    #                       Transmit Byte
    #####################################################################
    def tx_byte(b):
        global http_size, tx_cnt, tx_data, tx_flag
    
        if tx_flag == False:
            http_size = http_size + 1
            # print("tx byte: {0}, http size: {1}".format(hex(b), http_size))
            return
    
        # print("tx byte: {0}".format(hex(b)))
    
        tx_data[tx_cnt] = b
        tx_cnt = tx_cnt + 1
        if tx_cnt >= MAX_TX_SIZE:
            tx_flush()
    
    
    #####################################################################
    #                       Transmit DWORD
    #####################################################################
    def tx_dword(dw):
        tx_word(dw & 0xffff)
        tx_word((dw >> 16) & 0xffff)
    
    
    #####################################################################
    #                       Transmit Flush
    #####################################################################
    def tx_flush():
        global tx_cnt, tx_data
    
        if tx_cnt == 0:
            return
    
        r = modem.socket_tx(tx_data, tx_cnt)
        if not r:
            http_error = True
            return
    
        tx_cnt = 0
    
    
    #####################################################################
    #                       Transmit HTTP Headers
    #####################################################################
    def tx_http_headers(http_post, host_name, host_port):
        # example:
        # POST <http_post> HTTP/1.1
        # Host: <host_name>:<host_port>
        # Content-Length: <http_size>
        # Content-Type: application/octet-stream
        # <crlf>
        global http_error, http_size
    
        log("tx HTTP headers")
    
        if http_error:
            return
    
        s = "POST {0} HTTP/1.1\r\n".format(http_post)
        tx_string(s)
    
        if host_port != 80:
            s = "Host: {0}:{1}\r\n".format(host_name, host_port)
        else:
            s = "Host: {0}\r\n".format(host_name)
    
        tx_string(s)
        s = "Content-Length: {0}\r\n".format(http_size)
        tx_string(s)
        s = "Content-Type: application/octet-stream\r\n"
        tx_string(s)
        s = "\r\n"
        tx_string(s)
    
    
    #####################################################################
    #                       Transmit String
    #####################################################################
    def tx_string(s):
        b = s.encode('utf-8')
    
        for x in b:
            tx_byte(x)
        
    
    #####################################################################
    #                       Transmit WORD
    #####################################################################
    def tx_word(w):
        tx_byte(w & 0xff)
        tx_byte((w >> 8) & 0xff)
    


  • I seemed to have hit a major problem using the AT+SQNHTTPSND modem command. Although the manual does not state this, the maximum size of the data posted is apparently 1500 bytes.

    If anyone has ideas of how to increase this, please let me know. Unfortunately my app requires posting messages over 3000 bytes.

    Disappointed...



  • Here's updated code that is now running on two units overnight with good success. The code handles unsolicited responses gracefully. The code is non-intrusive to other multi-tasking threads. The code has not crashed (more testing to be done for sure). The code is easy to understand; everything is there to see and improve (no hidden commands being sent to the modem).

    # MODEM.PY Module
    
    import globals as g
    from machine import UART
    import micropython
    import sys
    import util
    from util import log
    from utime import sleep_ms, ticks_ms, ticks_diff
    
    uart = None
    
    #####################################################################
    #                     Send AT Command To Modem
    #####################################################################
    def at(cmd, filterx=""):
        try:
            if uart.any() > 0:
                # get unsolicited modem response 
                a = at_response()
    
                for s in a:
                    at_process(s)
    
            log("  modem command: {}".format(cmd))
    
            # send command to modem
            n = uart.write(cmd + '\r')
            if n != len(cmd) + 1:
                log("error sending command to modem: n = {}".format(n))
                return []
    
            a = at_response(filterx)
            return a
    
        except Exception as ex:
            sys.print_exception(ex)
            a = []
    
        return a    # return modem response lines in array
    
    
    #####################################################################
    #                     Filter Modem Response
    #####################################################################
    def at_filter(a, filterx):
        # a is passed as reference value
        if filterx == "":
            return
    
        # filter response
        n = len(filterx)
        i = len(a)
        while i > 0:
            i = i - 1
            if a[i][0:n] != filterx:
                # remove lines that do not start with filter value
                at_process(a[i])
                a.pop(i)
    
    
    #####################################################################
    #                     Process Unsolicited Response
    #####################################################################
    def at_process(s):
        if s == 'OK':
            pass
        else:
            log("unsolicited modem response: {}".format(s))
        return
    
    
    #####################################################################
    #                       Get AT Command Response
    #####################################################################
    def at_response(filterx=""):
        try:
            t0 = ticks_ms()
            
            while True:
                if uart.any() > 0:
                    # insure entire response has been received
                    sleep_ms(50)
                    break
    
                t1 = ticks_ms()
                tx = ticks_diff(t1, t0)
    
                if tx > 10000:
                    log("timeout error - no modem response after 10 secs")
                    return []
    
                sleep_ms(100)
    
            b = uart.read()
            s = str(b, 'utf-8')
            a = s.split('\r\n')
            a = list(filter(None, a))
    
            log("  modem response: {}".format(a))
            at_filter(a, filterx)
    
        except Exception as ex:
            sys.print_exception(ex)
            a = []
    
        return a    # return modem response lines in array
    
    
    #####################################################################
    #             Attach Cellular Modem To Packet Domain Service
    #####################################################################
    def attach():
        try:
            log("attach modem to packet domain service")
            a = at('AT+CGATT=1','OK')
            if len(a) == 0:
                log("error attaching modem")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                       Check Registration
    #####################################################################
    def check_registration():
        # return 0-5, 99-unknown
        # response: ['+CEREG: 2,4', 'OK']
        # response: ['+CEREG: 2,1,"2C29","0B54400F",7', 'OK']
        # 2,0 - not registered, not searching
        # 2,1 - registered, home network
        # 2,2 - not registered, searching
        # 2,3 - registration denied
        # 2,4 - unknown (out of coverage)
        # 2,5 - registered, roaming
    
        try:
            while True:
                log("check registration")
    
                a = at('AT+CEREG?','+CEREG:')
                if len(a) == 0:
                    break
    
                a = a[0].split(",")
    
                if (a[0] != "+CEREG: 2"):
                    break
                
                reg = int(a[1])
                if reg == 1:
                    log("registered - home network")
                elif reg == 5:
                    log("registered - roaming")
                else:
                    log("not registered")
    
                return reg
    
        except Exception as ex:
            log("check registration exception")
            sys.print_exception(ex)
    
        # unknown registration
        log("error checking registration")
        return 99
    
    
    #####################################################################
    #             Detach Cellular Modem From Packet Domain Service
    #####################################################################
    def detach():
        # modem does not get SMS messages while the modem is detached
        # old messages received while detached are only received when a new message is sent while attached
        try:
            log("detach modem from packet domain service")
            a = at('AT+CGATT=0','OK')
            if len(a) == 0:
                log("error detaching modem")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                       Disable LTE Modem
    #####################################################################
    def disable_modem():
        try:
            log("disable modem")
            a = at('AT+CFUN=0','OK')     # minimum functionality
            if len(a) == 0:
                log("error disabling modem")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                       Enable Modem
    #####################################################################
    def enable_modem():
        try:
            log("enabling modem")
            a = at('AT+CFUN=1','OK')     # full functionality
            if len(a) == 0:
                log("error enabling modem")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                Get CFUN - Modem Level of Functionality
    #####################################################################
    def get_cfun():
        # 0 - minimum functionality
        # 1 - full functionality
        # 4 - radios disabled but access to SIM allowed
        # -1 - unknown
        # note: if modem does +SHUTDOWN/+SYSSTART, CFUN will be reset to 0
        try:
            while True:
                a = at('AT+CFUN?','+CFUN:')
                # response: ['+CFUN: 1', 'OK']
    
                if len(a) == 0:
                    break
    
                cfun = int(a[0][7])
                return cfun
    
        except Exception as ex:
            sys.print_exception(ex)
    
        return -1
    
    
    #####################################################################
    #                           Get SMS Mode
    #####################################################################
    def get_sms_mode():
        # return 0-PDU mode or unknown, 1-text mode
    
        try:
            log("get SMS mode")
            a = at('AT+CMGF?','+CMGF:')
            # response: ['+CMGF: 1', 'OK']
            if len(a) == 0:
                return 0    # mode unknown
    
            mode = int(a[0][7])
            return mode
    
        except Exception as ex:
            sys.print_exception(ex)
    
        return 0    # mode unknown
    
    
    #####################################################################
    #                            HTTP Post          
    #####################################################################
    def http_post(uri, header, tx_data):
        # --> AT+SQNHTTPSND=<prof_id>,<command>,<resource>,<data_len>[,<post_param>[,<extra_header_line>]]
        # xx> POST <uri> HTTP/1.1
        # xx> <header>
        # xx> Content-Length: <tx_size>
        # xx> Content-Type: application/octet-stream
        # xx> <blank line>
        # <-- '> '
        # --> <tx_data bytes>
        # <-- OK
        # <-- +SQNHTTPRING: <prof_id,<http_status_code>,<content_type>,<rx_size>
        # --> AT+SQNHTTPRCV=1,0\r
        # <-- /r/n<<<
        # <-- <rx_data bytes>
        # <-- OK
        try:
            log("HTTP post")
    
            while True:
                # note: init_modem() sets configuration "AT+SQNHTTPCFG=..." at startup
                tx_size = len(tx_data)
    
                # log("writing message: {0}".format(tx_data))
                log("tx_data length: {0}".format(tx_size))
    
                # AT+SQNHTTPSND=<prof_id>,<command>,<resource>,<data_len>[,<post_param>[,<extra_header_line>]]
                # prof_id=1, command=0 (POST), <uri>, <tx_size>, post_parm="2" (application/octet-stream), header="Host: <host_name>" 
    
                a = at('AT+SQNHTTPSND=1,0,"{0}",{1},"2","{2}"'.format(uri, tx_size, header),'> ')
                if len(a) == 0:
                    break   # error
    
                uart.write(tx_data)
                a = at_response('OK')
                if len(a) == 0:
                    break   # error
    
                # modem responds with "+SQNHTTPRING: <prof_id,<http_status_code>,<content_type>,<data_size>"
                a = at_response("+SQNHTTPRING:")
                if len(a) == 0:
                    break   # error
    
                a = a[0].split(",")
                http_status_code = int(a[1])
                if http_status_code != 200:
                    break   # error
    
                rx_size = int(a[3])
                log("rx_data length: {0}".format(rx_size))
    
                # get response
                cmd = 'AT+SQNHTTPRCV=1,0\r'
                log("  modem command: {0}".format(cmd))
                uart.write(cmd)
    
                r = wait_rx(5, 10000)   # wait for b'\r\n<<<'
                if r == False:
                    break   # error
    
                b = uart.read(5)
                # log(" modem response: {0}".format(b))
                if b[2:5] != b'<<<':
                    break   # error
    
                t0 = ticks_ms()
            
                b = b''
    
                n = rx_size     # no. bytes remaining to be read
                while True:
                    if uart.any() > 0:
                        log("attempt to read {0} bytes".format(n))
                        bx = uart.read(n)
                        log("bytes read: {0}".format(len(bx)))
                        # log(" modem response: {0}".format(bx))
                        b = b + bx
                        if len(b) == rx_size:
                            break   # entire message received
                        n = rx_size - len(b)
                        t0 = ticks_ms()     # reset timeout
    
                    t1 = ticks_ms()
                    tx = ticks_diff(t1, t0)
                    if tx > 10000:
                        log("timeout error receiving response")
                        return b''
    
                    sleep_ms(400)
    
                log("total bytes read: {0}".format(len(b)))
                # log(" post response: {0}".format(b))
    
                a = at_response('OK')
                if len(a) == 0:
                    break   # error
    
                # log(b)
                return b
    
        except Exception as ex:
            sys.print_exception(ex)
    
        # error
        return b''
    
    
    #####################################################################
    #                     Get SIM Card ICCID Number
    #####################################################################
    def iccid():
        # CFUN must be 1 or 4
        try:
            log("get SIM card ICCID")
            a = at('AT+SQNCCID?','+SQNCCID:')
            # example response: ['+SQNCCID: "89014103271203065543",""', 'OK']
            if len(a) == 0:
                return ''
    
            a = a[0].split(",")
            n = len(a[0])
            r = a[0][11:n-1]
    
        except Exception as ex:
            sys.print_exception(ex)
            r = ''
    
        log("ICCID = {0}".format(r))
        return r    # ICCID as string
    
    
    #####################################################################
    #                       Get Modem IMEI Number
    #####################################################################
    def imei():
        try:
            log("get modem IMEI number")
            a = at('AT+CGSN=1','+CGSN:')
            # example response: ['+CGSN: "354347094028575"', 'OK']
            if len(a) == 0:
                return ''
    
            n = len(a[0])
            r = a[0][8:n-1]
    
        except Exception as ex:
            sys.print_exception(ex)
            r = ''
    
        log("IMEI = {0}".format(r))
        return r    # IMEI as string
    
    
    #####################################################################
    #                       Initialize Modem
    #####################################################################
    def init_modem():
        try:
            log("initializing modem")
    
            if uart == None:
                init_uart()
    
            disable_modem()
    
            # set profile #1 parameters for HTTP connection
            # prof_id=1 (profile), ip, port, auth_type=0 (None), username="", password="", 
            # ssl_enabled=0, timeout, cid=1 (PDN Context Identifier)
            server = g.oIni.host_ip     # note: host_name could also be used (auto DNS lookup)
            port = g.oIni.host_port
            timeout = 10    # secs to wait for response from server
            cmd = 'AT+SQNHTTPCFG=1,"{0}",{1},0,"","",0,{2},1'.format(server, port, timeout)
            a = at(cmd,'OK')
            if len(a) == 0:
                log("error initializing modem")
    
            set_sms_mode()
    
            enable_modem()
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #               Initialize Uart Connected To LTE Modem
    #####################################################################
    def init_uart():
        global uart
        # pins=(TXD, RXD, RTS, CTS)
        # FiPy: pins=('P20', 'P18', 'P19', 'P17')
        # GPy:  pins=('P5', 'P98', 'P7', 'P99')
        log("initializing UART")
        # rx_buffer_size: must be > 127, 200000 works, 250000 crashes, http_post seems to work with any size
        uart = UART(1, baudrate=921600, bits=8, parity=None, stop=1, timeout_chars=2, pins=('P5', 'P98', 'P7', 'P99'), rx_buffer_size=512)
    
    
    #####################################################################
    #           Is Cellular Modem Attached To Packet Domain Service
    #####################################################################
    def isattached():
        # returns: True/False
        try:
            a = at('AT+CGATT?','+CGATT:')
            # example response: ['+CGATT: 0', 'OK']
            if len(a) == 0:
                return False
    
            if a[0][8] == '1':
                return True
    
        except Exception as ex:
            sys.print_exception(ex)
    
        return False
    
    
    #####################################################################
    #                           Reset Modem
    #####################################################################
    def reset_modem():
        try:
            if uart == None:
                init_uart()
    
            log("reseting modem...")
            a = at('AT^RESET','+SHUTDOWN')
            # generates +SHUTDOWN ... +SYSSTART responses
            if len(a) == 0:
                log("error resetting modem - no +SHUTDOWN")
    
            a = at_response('+SYSSTART')
            if len(a) == 0:
                log("error resetting modem - no +SYSSTART")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                  Check Modem For Restart/Crash
    #####################################################################
    def restarted():
        # return True if modem has crashed / restarted
        try:
            # if CFUN != 1, modem has crashed / restarted
            cfun = get_cfun()
            if cfun != 1:
                return True
    
            # if SMS text mode is reset to zero, modem has crashed / restarted
            mode = get_sms_mode()
            if mode != 1:
                return True
    
            return False
    
        except Exception as ex:
            sys.print_exception(ex)
    
        return True
    
    
    #####################################################################
    #                           Set APN
    #####################################################################
    def set_apn():
        try:
            log("set APN")
    
            # ICCID is only valid after registration 
            r = iccid()[0:5]
            if r == "89014":
                apn = g.oIni.apn_89014   # Kore AT&T SIM
            elif r == "89012":
                apn = g.oIni.apn_89012   # Kore T-Mobile SIM
            elif r == "89445":
                apn = g.oIni.apn_89445   # Hologram SIM
            else:
                apn = g.oIni.apn_89014   # Kore AT&T SIM
    
            g.oIni.apn = apn
            log("APN: {0}".format(apn))
    
            # try to reduce wear of non-volatile memory
            a = at('AT+CGDCONT?','+CGDCONT:')
            # response --> ['+CGDCONT: 1,"IP","10569.mcs",,,,0,0,0,0,0,0', ...]
            if len(a) > 0:
                a = a[0].split(",")
                if (a[0] == '+CGDCONT: 1') and (a[1] == '"IP"') and (a[2] == '"'+apn+'"'):
                    return
    
            # apn needs setting
            cmd = 'AT+CGDCONT=1,"IP","{0}"'.format(apn)
            a = at(cmd,'OK')
            if len(a) == 0:
                log("error setting APN")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                       Set SMS Mode To Text
    #####################################################################
    def set_sms_mode():
        try:
            log("set SMS mode to text")
            a = at('AT+CMGF=1','OK')     # set SMS mode to text
            if len(a) == 0:
                log("error setting SMS mode to text")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                       Get Signal Strength
    #####################################################################
    def signal_strength():
        # 0-31, 99-unknown
        try:
            while True:
                log("check signal strength")
                a = at('AT+CSQ','+CSQ:')
                # example response: ['+CSQ: 18,99', 'OK'] where 18 is signal strength
                if len(a) == 0:
                    break
    
                n = len(a[0])
                s = a[0][6:n-1]
                a = s.split(",")
                cell_signal = int(a[0])
    
                g.oStatus.cell_signal = cell_signal
                log("signal strength = {0}".format(cell_signal))
                return cell_signal
    
        except Exception as ex:
            sys.print_exception(ex)
    
        # unknown signal strength
        g.oStatus.cell_signal = 99
        log("signal strength unknown")
        return 99
    
    
    #####################################################################
    #             Delete Read, Sent, and Unsent SMS Messages
    #####################################################################
    def sms_delete():
        try:
            log("delete all READ, SENT, and UNSENT SMS messages")
            a = at('AT+CMGD=1,3','OK')
            if len(a) == 0:
                log("error trying to delete read, sent, and unsent SMS messages")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                     Delete All SMS Messages
    #####################################################################
    def sms_delete_all():
        # doesn't work until some time after attach() is called
        try:
            log("delete all SMS messages")
            a = at('AT+CMGD=1,4','OK')
            if len(a) == 0:
                log("error trying to delete all SMS messages")
            
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                     Process SMS Messages
    #####################################################################
    def sms_process(r):
        # example response:
        # ['+CMGL: 1,"REC READ","+1xxxxxxxxxx",,"19/01/07,09:16:53-20"', 'Test3', '+CMGL: 2,"REC READ","+1xxxxxxxxxx",,"19/01/07,11:12:30-20"', 'Test4', 'OK']
        
        try:
            for m in r:
                if (m[0:5] == "+CMGL"):
                    continue
                
                a = m.split("=")
                cmd = a[0].upper()
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                      Read Unread SMS Messages
    #####################################################################
    def sms_read():
        # response example: ['+CMGL: 1,"REC UNREAD","+1xxxxxxxxxx",,"19/01/07,09:16:53-20"', 'Test3', 'OK']
        log("read unread SMS messages")
        a = at('AT+CMGL="REC UNREAD"')
        return a
        
    
    #####################################################################
    #                       Read All SMS Messages
    #####################################################################
    def sms_read_all():
        # response example:
        # ['+CMGL: 1,"REC READ","+1xxxxxxxxxx",,"19/01/07,09:16:53-20"', 'Test3', '+CMGL: 2,"REC READ","+1xxxxxxxxxx",,"19/01/07,11:12:30-20"', 'Test4', 'OK']
        log("read all SMS messages")
        a = at('AT+CMGL="ALL"')
        return a
    
    
    #####################################################################
    #                       Wait For N Received Chars          
    #####################################################################
    def wait_rx(n, timeout=10000):
        # timeout in msecs
        t0 = ticks_ms()
        while True:
            if uart.any() >= n:
                break
    
            t1 = ticks_ms()
            tx = ticks_diff(t1, t0)
            if tx > timeout:
                return False
        
            sleep_ms(10)
            
        return True
    
    

    Here's the code being used. The code shown is incomplete since it is application dependent. I'm somewhat disappointed in the necessary placement of the modem.apn_set() call. This may change in the future.

    # COM.PY Module
    
    import globals as g
    import modem
    from poll import poll
    import pycom
    import sys
    import uos
    import util
    from util import log
    from utime import sleep_ms
    import wifi
    
    #####################################################################
    #                         Communication Task
    #####################################################################
    def com_task():
        try:
            sleep_ms(500)
            log("com_task: started")
            
            wifi.deinit()
            modem.reset_modem()
            modem.init_modem()
    
            g.poll_host = True      # triggers poll at startup
    
        except Exception as ex:
            sys.print_exception(ex)
    
        while True:
            try:
                if modem_ready():
                    if ready_to_poll():
                        modem.set_apn()
                        transmit()
    
                sleep_ms(2000)
    
            except Exception as ex:
                sys.print_exception(ex)
    
    
    #####################################################################
    #                           Modem Ready
    #####################################################################
    def modem_ready():
        try:
            log("** check for modem ready")
    
            # get modem signal strength
            g.oStatus.cell_signal = modem.signal_strength()
            
            # check modem registration
            r = modem.check_registration()
            if (r == 1) or (r == 5):
                # registered
                g.com_secs = 0
    
                # handle SMS messages
                r = modem.sms_read()
                if len(r) > 1:
                    modem.sms_process(r)
                    modem.sms_delete()
    
                return True
            
            reset = False
    
            if g.com_secs > (10*60):
                # unable to attach in 10 mins, try resetting modem
                reset = True
                
            if modem.restarted():
                # modem has crashed / restarted, try resetting modem
                reset = True
    
            if reset:    
                modem.reset_modem()
                modem.init_modem()
                g.com_secs = 0
    
            return False
    
        except Exception as ex:
            sys.print_exception(ex)
        
        return False
    
    


  • @kjm What would really be neat is if we could learn how to put the modem in a mode that allowed the urequests/usockets libraries to work using just AT commands!

    I suspect it has to do with the AT+CGDCONT parameter named PDP_type. The manual shows the following values:

    X.25 ITU-T/CCITT X.25 layer 3 (Obsolete)
    IP Internet Protocol (IETF STD 5 [103])
    IPV6 Internet Protocol, version 6 (see RFC 2460 [106])
    IPV4V6 Virtual <PDP_type> introduced to handle dual IP stack UE capability. (See
    3GPP TS 24.301 [83])
    OSPIH Internet Hosted Octect Stream Protocol (Obsolete)
    PPP Point to Point Protocol (IETF STD 51 [104])
    Non-IP Transfer of Non-IP data to external packet data network (see 3GPP TS 23.401

    This is an area I'm unsure about. I would welcome comments from others about what would need to be done.



  • @kjm Thanks for the comment. The intention of wait_rx(n, timeout=10000) is to be a non-blocking call that waits for N chars to come into the uart or to timeout after 10,000 msecs by default. N should be less than the buffer size of the uart which is currently set to 512 bytes.

    In looking at my current code, I see a bug. I should have had a sleep command in the while loop to make multi-tasking more efficient. Here's the corrected code. Thanks again!

    #####################################################################
    #                       Wait For N Received Chars          
    #####################################################################
    def wait_rx(n, timeout=10000):
        # timeout in msecs
        t0 = ticks_ms()
        while True:
            if uart.any() >= n:
                break
    
            t1 = ticks_ms()
            tx = ticks_diff(t1, t0)
            if tx > timeout:
                return False
        
            sleep_ms(10)
            
        return True
    


  • @kjm I think I remember having to modify urequests also. Here's what I currently use in my old version that is working.

    import usocket
    import util
    
    class Response:
    
        def __init__(self, f):
            self.raw = f
            self.encoding = "utf-8"
            self._cached = None
    
        def close(self):
            if self.raw:
                self.raw.close()
                self.raw = None
            self._cached = None
    
        @property
        def content(self):
            if self._cached is None:
                try:
                    self._cached = self.raw.read()
                finally:
                    self.raw.close()
                    self.raw = None
            return self._cached
    
        @property
        def text(self):
            return str(self.content, self.encoding)
    
        def json(self):
            import ujson
            return ujson.loads(self.content)
    
    
    def request(method, url, data=None, json=None, headers={}, stream=None):
        try:
            proto, dummy, host, path = url.split("/", 3)
        except ValueError:
            proto, dummy, host = url.split("/", 2)
            path = ""
        if proto == "http:":
            port = 80
        elif proto == "https:":
            import ussl
            port = 443
        else:
            raise ValueError("Unsupported protocol: " + proto)
    
        if ":" in host:
            host, port = host.split(":", 1)
            port = int(port)
    
        # ai = usocket.getaddrinfo(host, port, 0, usocket.SOCK_STREAM)  # PATCH
        ai = usocket.getaddrinfo(host, port)
        ai = ai[0]
    
        s = usocket.socket(ai[0], ai[1], ai[2])
        try:
            s.settimeout(20)
    
            s.connect(ai[-1])
    
            if proto == "https:":
                s = ussl.wrap_socket(s, server_hostname=host)
            
            s.write(b"%s /%s HTTP/1.0\r\n" % (method, path))
            
            if not "Host" in headers:
                s.write(b"Host: %s\r\n" % host)
            
            # Iterate over keys to avoid tuple alloc
            for k in headers:
                s.write(k)
                s.write(b": ")
                s.write(headers[k])
                s.write(b"\r\n")
    
            if json is not None:
                assert data is None
                import ujson
                data = ujson.dumps(json)
                s.write(b"Content-Type: application/json\r\n")
    
            if data:
                s.write(b"Content-Length: %d\r\n" % len(data))
    
            s.write(b"\r\n")
    
            if data:
                s.write(data)
    
            l = s.readline()
            #print(l)
            l = l.split(None, 2)
            status = int(l[1])
            reason = ""
            if len(l) > 2:
                reason = l[2].rstrip()
    
            while True:
                l = s.readline()
                if not l or l == b"\r\n":
                    break
                #print(l)
                if l.startswith(b"Transfer-Encoding:"):
                    if b"chunked" in l:
                        raise ValueError("Unsupported " + l)
                elif l.startswith(b"Location:") and not 200 <= status <= 299:
                    raise NotImplementedError("Redirects not yet supported")
    
    #   except OSError:     # PATCH
        except:
            s.close()
            raise
    
        resp = Response(s)
        resp.status_code = status
        resp.reason = reason
        return resp
    
    
    def head(url, **kw):
        return request("HEAD", url, **kw)
    
    def get(url, **kw):
        return request("GET", url, **kw)
    
    def post(url, **kw):
        return request("POST", url, **kw)
    
    def put(url, **kw):
        return request("PUT", url, **kw)
    
    def patch(url, **kw):
        return request("PATCH", url, **kw)
    
    def delete(url, **kw):
        return request("DELETE", url, **kw)
    
    


  • @tlanier Admire your efforts squire. I've been struggling with lte for a year or so now. It's not perfect (the lte.isattached() gets confused sometimes) but I got it robust enough to be usable. I use the requests library for data transfer & my main complaint is that it can't be timed out. I modified it with machine.WDT so that I can abort in a timely manner but I'd like a better solution. Am I right in thinking your wait_rx(n, 10000) allows you to quit if http post/get times out after 10s?



  • @peterp Sorry to take so long to respond. I wanted to finish updating my posts showing the new code that seems to be working well. Soon I should be able to post the entire refined code. Maybe it will help others with the same problems we have had.

    The reason I went down this development path was as described originally:

    "I currently have a program working in production using Pycom MicroPython V1.20.0.rc13 on many units. When I try to run the same program on a newly purchased GPy running Pycom MicroPython 1.20.2.r3, the program crashes (20 sec watchdog timeout) when I do an AT command ('AT+CEREG?') after disconnecting from a successful transmission. How do I troubleshoot such a crash?"

    Our original reason for picking Pycom and GPy was the thinking that all the modem complexity would be handled by the high level LTE module. It's only a guess but our thinking that since the crashes always happened during times communicating with the modem, the LTE module was the likely source of the problem.

    The new method seems to be superior from the standpoint of interference with multiple tasks. Since we always call non-blocking uart commands, the code should never get hung in the C code for any period. A simple example of the LTE module code freezing multi-tasking is to do a simple modem reset. Reading and writing to the file storage also has a minor affect. The real reason for the development was to try to eliminate program crashes. Only longer term testing will show whether we have achieved that goal.

    One concern I do have is whether I am properly initializing the cell modem. Any input from anybody out there that is more familiar with properly setting up the LTE modem would be appreciated. It seems to work fine at this point; however, I'm not sure whether it's working because the GPy I'm testing with has run the LTE initialization at some point in the past and that has possibly setup the non-volatile memory of the modem to the proper settings that are needed.

    One drawback of using this method of transmission is it is not compatible with WIFI connections. That is not an issue for us at this time. Maybe later we can research how to do some form of communication that is compatible with both WIFI and direct AT commands. I assume that involves using the socket commands of the modem, but this is an area I'm not sure about at this time.



  • Here's some of the higher level code that uses the modem module.

    import globals as g
    import modem
    from poll import poll
    import pycom
    import sys
    import uos
    import util
    from util import log
    from utime import sleep_ms
    import wifi
    
    #####################################################################
    #                         Communication Task
    #####################################################################
    def com_task():
        try:
            sleep_ms(500)
            log("com_task: started")
            
            wifi.deinit()
            modem.reset_modem()
            modem.init_modem()
    
            g.poll_host = True      # triggers poll at startup
    
        except Exception as ex:
            sys.print_exception(ex)
    
        while True:
            try:
                if modem_ready():
                    if ready_to_poll():
                        modem.set_apn()
                        transmit()
    
                sleep_ms(2000)
    
            except Exception as ex:
                sys.print_exception(ex)
    
    
    #####################################################################
    #                           Modem Ready
    #####################################################################
    def modem_ready():
        try:
            log("** check for modem ready")
    
            # get modem signal strength
            g.oStatus.cell_signal = modem.signal_strength()
            
            # check modem registration
            r = modem.check_registration()
            if (r == 1) or (r == 5):
                # registered
                g.com_secs = 0
    
                # handle SMS messages
                r = modem.sms_read()
                if len(r) > 1:
                    modem.sms_process(r)
                    modem.sms_delete()
    
                return True
            
            reset = False
    
            if g.com_secs > (10*60):
                # unable to attach in 10 mins, try resetting modem
                reset = True
                
            if modem.restarted():
                # modem has crashed / restarted, try resetting modem
                reset = True
    
            if reset:    
                modem.reset_modem()
                modem.init_modem()
                g.com_secs = 0
    
            return False
    
        except Exception as ex:
            sys.print_exception(ex)
        
        return False
    
    

  • Global Moderator

    Hey @tlanier could you elaborate a bit on this point? How to reproduce this freezing?

    Task switching no longer freezes during modem communication.



  • The new at(cmd, filter="") function is now improved such that unsolicited responses should have no affect. It also allows you to specify the response you are interested in getting back by setting the filter parameter. This simplifies the coding of the rest of the modem module.

    #####################################################################
    #                     Send AT Command To Modem
    #####################################################################
    def at(cmd, filterx=""):
        try:
            if uart.any() > 0:
                # get unsolicited modem response 
                a = at_response()
    
                for s in a:
                    at_process(s)
    
            log("  modem command: {}".format(cmd))
    
            # send command to modem
            n = uart.write(cmd + '\r')
            if n != len(cmd) + 1:
                log("error sending command to modem: n = {}".format(n))
                return []
    
            a = at_response(filterx)
            return a
    
        except Exception as ex:
            sys.print_exception(ex)
            a = []
    
        return a    # return modem response lines in array
    
    
    #####################################################################
    #                     Filter Modem Response
    #####################################################################
    def at_filter(a, filterx):
        # a is passed as reference value
        if filterx == "":
            return
    
        # filter response
        n = len(filterx)
        i = len(a)
        while i > 0:
            i = i - 1
            if a[i][0:n] != filterx:
                # remove lines that do not start with filter value
                at_process(a[i])
                a.pop(i)
    
    
    #####################################################################
    #                     Process Unsolicited Response
    #####################################################################
    def at_process(s):
        if s == 'OK':
            pass
        else:
            log("unsolicited modem response: {}".format(s))
        return
    
    
    #####################################################################
    #                       Get AT Command Response
    #####################################################################
    def at_response(filterx=""):
        try:
            t0 = ticks_ms()
            
            while True:
                if uart.any() > 0:
                    # insure entire response has been received
                    sleep_ms(50)
                    break
    
                t1 = ticks_ms()
                tx = ticks_diff(t1, t0)
    
                if tx > 10000:
                    log("timeout error - no modem response after 10 secs")
                    return []
    
                sleep_ms(100)
    
            b = uart.read()
            s = str(b, 'utf-8')
            a = s.split('\r\n')
            a = list(filter(None, a))
    
            log("  modem response: {}".format(a))
            at_filter(a, filterx)
    
        except Exception as ex:
            sys.print_exception(ex)
            a = []
    
        return a    # return modem response lines in array
    


  • @jcaron Thanks for the suggestion. I have been thinking about that. I would need to make the module more general purpose and less specific to my application. My first priority is to make our application more robust and error free.

    I've thought about creating a general purpose do nothing application that implements multi-threading, a timer interrupt service routine, and the modem module to show how everything fits together. Someone could take the template application and create a full application in no time.

    Including our method of program updates would also be useful I think.



  • @tlanier you should probably create a GitHub or GitLab repo for your code...



  • A new method has been added to the modem module. It is desirable to use the ICCID to determine which APN to set. One issue to deal with is apparently the ICCID is not valid until registration with the tower is done. The set_apn() method should be called right before doing the attach().

    To reduce the wear of writing to the non-volatile memory, I read the current value of the APN and skip the write if not necessary. I wonder if the modem does this type of checking internally? Ideally we could just set the APN once at program start, but we can't read the ICCID at that point for some reason. Even though the manual says when CFUN=4 or CFUN=1 access to the SIM is available, reading the ICCID does not work until after registration.

    To get some context as to how the modem module can be used, I've included example code for a modem_ready() method that uses the modem module.

    There is still work to be done with the basic at() and get_modem_response() methods. Unsolicited responses are causing problems in some cases. That will be my next area to concentrate on. There seems to be two paths to take when talking to a modem. Path #1 sends a command to the modem and then waits a period of time and assumes the modem has had time to respond completely. Path #2 sends a command to the modem and then watches the data being returned looking for (1) OK, or (2) ERROR anywhere in the response. The responses then must be filtered to only return the particular response line that is desired.

    #####################################################################
    #                           Set APN
    #####################################################################
    def set_apn():
        try:
            log("set APN")
    
            # ICCID is only valid after registration 
            r = iccid()[0:5]
            if r == "89014":
                apn = g.oIni.apn_89014   # Kore AT&T SIM
            elif r == "89012":
                apn = g.oIni.apn_89012   # Kore T-Mobile SIM
            elif r == "89445":
                apn = g.oIni.apn_89445   # Hologram SIM
            else:
                apn = g.oIni.apn_89014   # Kore AT&T SIM
    
            g.oIni.apn = apn
            log("APN: {0}".format(apn))
    
            # try to reduce wear of non-volatile memory
            a = at('AT+CGDCONT?')
            # response --> ['+CGDCONT: 1,"IP","10569.mcs",,,,0,0,0,0,0,0', ...]
            s = a[0]
            a = s.split(",")
            if (a[0] == '+CGDCONT: 1') and (a[1] == '"IP"') and (a[2] == '"'+apn+'"'):
                return
    
            # apn needs setting
            a = at('AT+CGDCONT=1,"IP","{0}"'.format(apn))
            if a[0] != 'OK':
                log("error setting APN")
    
        except Exception as ex:
            sys.print_exception(ex)
    
    
    #####################################################################
    #                           Modem Ready
    #####################################################################
    def modem_ready():
        try:
            log("** check for modem ready")
    
            # get modem signal strength
            g.oStatus.cell_signal = modem.signal_strength()
            
            # handle SMS messages
            r = modem.sms_read()
            if len(r) > 1:
                modem.sms_process(r)
                modem.sms_delete()
    
            # check modem registration
            r = modem.check_registration()
            if (r == 1) or (r == 5):
                # wait until registered to set APN
                modem.set_apn()
                
                modem.attach()
                if modem.isattached():
                    g.com_secs = 0
                    return True
            
            reset = False
    
            if g.com_secs > (10*60):
                # unable to attach in 10 mins, try resetting modem
                reset = True
                
            if modem.restarted():
                # modem has crashed / restarted, try resetting modem
                reset = True
    
            if reset:    
                modem.reset_modem()
                modem.init_modem()
                g.com_secs = 0
    
            return False
    
        except Exception as ex:
            sys.print_exception(ex)
        
        return False
    
    
    


  • @jcaron Agreed. Also, just wanted to confirm about the MTU. Would the MTU for NB-IoT be 680 bits (85 bytes) DL and 1000 bits (125 bytes) UL. Referred Section 8.2 NB-IoT Deployment Guide



  • @bitvijays In my case the response to a HTTP Post is a large file (208K file used to update the program). The program hangs in a loop retrieving whatever is in the UART receive buffer until the correct number of bytes is received (or timeout occurs).



  • @bitvijays HTTP is based on TCP, so any HTTP payload would indeed be sent as multiple packets (the size and number of which depend on the path MTU). TCP normally makes use of windowing, so it would not even necessarily send all at once, it would wait for ACKs along the way and send more as the first ACKs are received.

    It's interesting how this is all built into the modem itself...


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