Re: [Discuss-gnuradio] CRC check

Hi,

the problem is that the string "packet decoding" doesn't appear anywhere in the current GNU Radio source code, so I'm still not sure which block you are using. Also, crc.check_crc32 is used in two different blocks, so I can't even tell this way what we are talking about :(
Can you actually make sure twice you got the letter-for-letter right name of the "packet decoding" block?

Best regards,
marcis

On 21.02.2016 13:38, SangHyuk Kim wrote:

Thank Marcus.

"packet decoding" recovers message from received packet 

and i got false from crc.py

def check_crc32(s):

    if len(s) < 4:

        return (False, '')

    msg = s[:-4]

    #print "msg = '%s'" % (msg,)

    actual = digital.crc32(msg)

    (expected,) = struct.unpack(">I", s[-4:])

    #print "actual =", hex(actual), "expected =", hex(expected)

    print actual == expected

    return (actual == expected, msg)

2016-02-21 20:52 GMT+09:00 Marcus Müller <marcus.mueller@ettus.com>:

Dear Sang Hyuk Kim,

what "packet decoding" are you specifically talking about, and could you show us the code you've modified?

Best regards,
Marcus

On 21.02.2016 12:32, SangHyuk Kim wrote:

Hi, I transmit simple text file using two USRP N210

Tx)

file source -> packet encoding -> mod(GMSK) -> usrp sink

Rx)

usrp source -> demod(GMSK) -> packet decoding -> file sink

To make corrupt packet, I tried to modify part of crc check

I guess if the crc of received packet doesn't match with original one, receiver would discard the packet.

However, I found receiver accepts every packet even if crc check returns 'false'.

(I expected receiver accepts packet only pass crc check by 'true')

 Why it always return false and how can I corrupt packet with other ways ?

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