Receive USRP data on lopy lora

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 04:08:24 GMT

nilam — Fri, 30 Mar 2018 04:08:24 GMT

i tried to receive data from USRP, my code to receive data is
rx_data = s.recv(64)
if(rx_data):
print("Received data: "+str(rx_data))

received data is not in properly decoded
it displays some things like this:

Rx_cnt:12
(rx_timestamp=2217324419, rssi=-78, snr=1.0, sfrx=8, sftx=0, tx_trials=0)
Received data: b'\xbd\xca'
Rx_cnt:13
(rx_timestamp=2218930349, rssi=-79, snr=2.0, sfrx=8, sftx=0, tx_trials=0)
Received data: b'\xc5+*\xfe'
Rx_cnt:14
(rx_timestamp=2219519010, rssi=-75, snr=1.0, sfrx=8, sftx=0, tx_trials=0)
Received data: b'\xe7\xdfl\xfb'
Rx_cnt:15
(rx_timestamp=2220686254, rssi=-84, snr=-0.0, sfrx=8, sftx=0, tx_trials=0)
Received data: b'\xad\xee'
Rx_cnt:16
(rx_timestamp=2221272054, rssi=-77, snr=2.0, sfrx=8, sftx=0, tx_trials=0)
Received data: b'\x95\xe7\xb8\xfa\xf0c\xee'
Rx_cnt:17
(rx_timestamp=2221760271, rssi=-93, snr=-3.0, sfrx=8, sftx=0, tx_trials=0)
how to decode to get hex bytes or string text output

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 06:41:59 GMT

robert-hh — Fri, 30 Mar 2018 06:41:59 GMT

@nilam You'll get hex ascii representation with ubinascii.hexlify(), like:

import ubinascii
print("Received data: ", ubinascii.hexlify(rx_data))

I the samples you gave there are almost no printable characters, so displaying it as ASCII is not that useful.

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 06:57:27 GMT

nilam — Fri, 30 Mar 2018 06:57:27 GMT

@robert-hh what is the format of received data? like b'\xc5+*\xfe'.
is it utf-8? base64?
Sorry, i am asking very basic .

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 07:05:02 GMT

robert-hh — Fri, 30 Mar 2018 07:05:02 GMT

@nilam Python displays it as a mix of hex and ascii. so at
b'\xc5+*\xfe' you have 4 bytes, two of them, + and * are printable. I made a little hexdump function, which translates that to the usual way. It expects an bytes object as input

#
# Hexdump Function
#
FILTER=''.join([(len(repr(chr(x)))==3) and chr(x) or '.' for x in range(256)])

def hexdump(src, length=16):
    N=0; result=''
    while src:  # loop through string
       s,src = src[:length],src[length:]
       hexa = ' '.join(["%02X"%x for x in s])
       s = ''.join([FILTER[s[_]] for _ in range(len(s))])
       result += "%04X   %-*s   %s\n" % (N, length*3, hexa, s)
       N += length
    return result

so hexdump(b'\xc5+*\xfe') returns:

0000   C5 2B 2A FE                                        .+*.\n

As a side note: if you enclose you code with lines, that consist of three backticks (```), it gets printed accodingly

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 10:02:31 GMT

nilam — Fri, 30 Mar 2018 10:02:31 GMT

@robert-hh thank you for quick response.

Reply to Receive USRP data on lopy lora on Fri, 30 Mar 2018 12:00:43 GMT

robert-hh — Fri, 30 Mar 2018 12:00:43 GMT

@nilam Just to be pedantic, I simplified hexdump a bit. This is old code, collected when I started with Python.

FILTER=''.join([(len(repr(chr(x)))==3) and chr(x) or '.' for x in range(256)])

def hexdump(src, length=16):
    N=0; result=''
    while src:  # loop through string
       s,src = src[:length],src[length:]
       hexa = ' '.join(["%02X"%x for x in s])
       s = ''.join([FILTER[_] for _ in s])
       result += "%04X   %-*s   %s\n" % (N, length*3, hexa, s)
       N += length
    return result

I have my doubts whether I did all of that myself at that time, especially the FILTER= .. expression.