Re: [Discuss-gnuradio] CRC check

[Marcus Müller]

Hi Jawad,

ahhh you're right, of course! I was missing that the callback actually is set in the grc xml file to a lambda that calls recv_packet, so that's where the checking whether the CRC was correct happens :)
So, yes, I think the logic involved here is OK, but Sang Hyuk is still seeing problems.
So: You say packets for which the CRC is not correct still get accepted. What does "accepted" mean in the context? as far as I can tell, they don't get inserted into the output message queue:

    def recv_pkt(self, ok, payload):
        msg = gr.message_from_string(payload, 0, self._item_size_out,
                                     len(payload)/self._item_size_out)
        if ok: self._msgq_out.insert_tail(msg)

because for them, "ok" is "False".
Do they still appear on the output of the packet decoder?


Best regards,
Marcus

On 21.02.2016 15:22, Jawad Seddar wrote:

Hi all,

The packet decoder block uses packet_utils module (namely the packet_utils.unmake_packet() function) found in gr-digital.

The crc check occurs in the unmake_packet function.

The logic in that function is correct, what do you think is wrong with returning actual == expected?

Regards,
Jawad

Le 21 févr. 2016 14:26, "Marcus Müller" <address@hidden> a écrit :

OK, sadly that means I'm even more confused :(
packet_decoder doesn't have any CRC checking!

Best regards,
Marcus

On 21.02.2016 14:20, SangHyuk Kim wrote:

No! I'm using current version. the link was just for showing.!

2016-02-21 22:14 GMT+09:00 Marcus Müller <address@hidden>:

Hi,

thanks! Now it's clear what you're using :)
Is there a reason why you used a link to an outdated version of the file from 2011?

Best regards,
Marcus

On 21.02.2016 14:02, SangHyuk Kim wrote:

I'm using "packet_decoder" (http://goo.gl/7uVDDa)

2016-02-21 21:51 GMT+09:00 Marcus Müller <address@hidden>:

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 <address@hidden>:

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 ?

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio