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Ok, I made a little more progress today.
One of the problematic aspects of coding modem communication routines is knowing what to do when errors occur and how to reliably handle unsolicited modem responses. Currently I've decided against throwing exceptions in the functions. The calling program will need to decide what to do if errors occur.
I've upgraded the at() function to look for unsolicited responses before transmitting the requested command. If anything is in the RX buffer, it is assumed to be an unsolicited response. There is always a remote chance that an unsolicited response will arrive during the transmission of the command. This will mess up the expected response received.
I will later try to identify specific unsolicited responses the modem may emit. Currently I've noticed it emits a "+CEREG" on occassion. This can be turned off if we decide to later.
from machine import UART
from utime import sleep_ms, ticks_ms, ticks_diff
uart = None
#####################################################################
# Initialize Uart Connected To LTE Modem
#####################################################################
def init_uart():
global uart
# FiPy: pins=('P20', 'P18', 'P19', 'P17')
# GPy: pins=('P5', 'P98', 'P7', 'P99')
uart = UART(1, baudrate=921600, pins=('P5', 'P98', 'P7', 'P99'), timeout_chars=2)
#####################################################################
# Send AT Command To Modem
#####################################################################
def at(cmd):
try:
if uart.any() > 0:
# get unsolicited modem response
a = get_modem_response()
if len(a) > 0:
print("unsolicited modem response: {}".format(a))
# process unsolicited results here
print("modem command: {}".format(cmd))
# send command to modem
n = uart.write(cmd + '\r\n')
if n != len(cmd) + 2:
print("error sending command to modem: n = {}".format(n))
return []
a = get_modem_response()
except Exception as ex:
sys.print_exception(ex)
a = []
return a # return modem response
#####################################################################
# Get Modem Response
#####################################################################
def get_modem_response():
try:
t0 = ticks_ms()
while True:
if uart.any() > 0:
# insure entire response has been received
sleep_ms(1)
break
t1 = ticks_ms()
tx = ticks_diff(t1, t0)
if tx > 10000:
print("timeout error - no modem response after 10 secs")
return []
sleep_ms(100)
r = uart.read()
s = str(r, 'utf-8')
a = s.split('\r\n')
a = list(filter(None, a))
print("modem response: {}".format(a))
except Exception as ex:
sys.print_exception(ex)
a = []
return a # return modem response
#####################################################################
# Test Modem Module
#####################################################################
def test():
init_uart()
r = at("ATZ")
if (r[0] != 'OK'):
print("error")
r = at("AT+CEREG?")
if (r[1] != 'OK'):
print("error")
s = iccid()
print("ICCID: " + s)
s = imei()
print("IMEI: " + s)
n = signal_strength()
print("Signal Strength: " + str(n))
print("End of test")
#####################################################################
# Get SIM Card ICCID Number
#####################################################################
def iccid():
try:
a = at("AT+SQNCCID?")
# example response: ['+SQNCCID: "89014103271203065543",""', 'OK']
if a[1] != 'OK':
return ''
s = a[0]
if s[0:10] != '+SQNCCID: ':
return ''
a = s.split(",")
n = len(a[0])
r = a[0][11:n-1]
except Exception as ex:
sys.print_exception(ex)
r = ''
return r
#####################################################################
# Get Modem IMEI Number
#####################################################################
def imei():
try:
a = at("AT+CGSN=1")
# example response: ['+CGSN: "354347094028575"', 'OK']
if a[1] != 'OK':
return ''
s = a[0]
if s[0:7] != '+CGSN: ':
return ''
n = len(s)
r = s[8:n-1]
except Exception as ex:
sys.print_exception(ex)
r = ''
return r
#####################################################################
# Get Signal Strength
#####################################################################
def signal_strength():
# 0-31, 99-unknown
try:
while True:
a = at('AT+CSQ')
# example response: ['+CSQ: 18,99', 'OK'] where 18 is signal strength
if a[1] != 'OK':
break
s = a[0]
if (s[0:6] != "+CSQ: "):
break
n = len(s)
s = s[6:n-1]
a = s.split(",")
cell_signal = int(a[0])
return cell_signal
except Exception as ex:
sys.print_exception(ex)
# unknown signal strength
return 99
