# Post Binary Slicer question

**URL:** <https://www.ruby-forum.com/t/post-binary-slicer-question/240727>\
**Category:** GNU Radio\
**Created:** [April 28, 2014, 1:28am UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727 "2014-04-28T01:28:15Z")\
**Posts on this page:** 15\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [April 28, 2014, 1:28am UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/1 "2014-04-28T01:28:15Z")

</div>

I have a question about handling data after binary slicing in the  
demodulation portion of handling a signal. Currently I am taking that  
data  
and pushing it through the Correlate Access Code block then into a file  
sink. This produces a data file. I didn’t know if someone could tell me  
a  
block or method that will output the binary stream (or hex stream) to a  
file or stdout for real-time view of the pack contents. Currently I have  
some python code that converts that data file into binary/hex which is  
not  
idea.

Thanks,

Jay

Jay R.  
Twitter: @jradcliffe02  
E-Mail:  
removed\_email\_address@domain.invalid[https://mail.google.com/mail/?view=cm&fs=1&tf=1&to=removed\_email\_address@domain.invalid](https://mail.google.com/mail/?view=cm&fs=1&tf=1&to=removed_email_address@domain.invalid)  
LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 28, 2014, 5:13am UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/2 "2014-04-28T05:13:25Z")

</div>

mkfifo my\_fifo.bin  
hexdump my\_fifo.bin

Point your file sink to the my\_fifo.bin and turn off the buffering. It  
will  
then dump the data to the terminal in real time.

Lou  
KD4HSO

Jay R. wrote

> Jay
> 
> Jay R.  
> Twitter: @jradcliffe02  
> E-Mail:

> jay.radcliffe@

> \<[https://mail.google.com/mail/?view=cm&amp;fs=1&amp;tf=1&amp;to=](https://mail.google.com/mail/?view=cm&amp;fs=1&amp;tf=1&amp;to=)

> jay.radcliffe@

> \>  
> LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)
> 
> * * *
> 
> Discuss-gnuradio mailing list

> Discuss-gnuradio@

> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 28, 2014, 5:29am UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/3 "2014-04-28T05:29:59Z")

</div>

Jay,

Thanks for the inquiry. Is there a specific protocol or format you are  
trying to work with? Are the frame size fixed in length or variable?  
The  
answers to these questions will dictate whether you can use an existing  
block or if you will need to write your own.

Writing a block to parse things after the correlate access code block is  
relatively straight-forward. If you are using the (tag) version of that  
block, you simply need to look for the presence of that tag to delineate  
the start of a frame.

-John

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 9:21am UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/4 "2014-04-30T09:21:49Z")

</div>

On 29.04.2014 22:43, Jay R. wrote:

> The protocol is unknown at this time. I need to see the packets to  
> figure some of this out.

Jay,

does the QT GUI Time Raster sink help you in any way?

M

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 29, 2014, 10:45pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/5 "2014-04-29T22:45:17Z")

</div>

The protocol is unknown at this time. I need to see the packets to  
figure  
some of this out.

Ideally, I would like to see the entire packet (including the preamble  
and  
sync word) to start to work my way to the format of the packets from  
there.  
I am using the power squelch with the gate to limit the captures to  
just  
when a signal is over a certain strength. In a perfect world, I would  
like  
to have “Binary Slicer” → “File Sink” where the file contents are the  
binary stream (10101010101010 not to be confused for a binary file) or  
hex  
output (0xAA 0xAA). I could probably tag the preamble in with the  
Correlate Access Code?

Jay R.  
Twitter: @jradcliffe02  
E-Mail: removed\_email\_address@domain.invalid  
LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 5:11pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/6 "2014-04-30T17:11:15Z")

</div>

Jay,

If you stream the output of the correlate access code to file, and you  
leave them unpacked, Bit 1 being set will show where the sync word is (I  
think the bit after). Of course Bit 0 will be the data. This assumes  
you’re using correlate access code, and not “correlate access code -  
tag”.  
This should allow you to store everything including the preamble.

Also, if you don’t know the protocol, how do you know what the preamble  
is?

-John

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 4:21pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/7 "2014-04-30T16:21:10Z")

</div>

I guess I’m confused then. I’m using the hex FIFO dump as I described  
to  
examine AX.25 packets one bit at a time. Since the output of the slicer  
is  
a byte whose LSB is the only thing you are interested in, I believe you  
can  
use the unpacked-to-packed block to strip off the LSB from 8 bytes and  
pack  
those into a single byte; at least I’m using packed-to-unpacked to feed  
a  
binary file to a modulator so the reverse should work. Run that into a  
FIFO  
and dump with xxd - bits. Baudline is also handy for visually scrolling  
through the binary stream, although it’s visually irritating with only  
one  
sample per symbol.

Lou

Jay R. wrote

> output (0xAA 0xAA). I could probably tag the preamble in with the  
> Correlate Access Code?
> 
> Jay R.  
> Twitter: @jradcliffe02  
> E-Mail:

> jay.radcliffe@

> LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 5:24pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/8 "2014-04-30T17:24:03Z")

</div>

Maybe I should rephrase: I don’t know the entire protocol. I know there  
is  
a preamble, and I know the sync word. I know the packets are not fixed  
length, I know there is a CRC. This can all be determined from looking  
at  
the register settings for the CC1101 chip. The format of the data  
portion  
of transmission I do not know. In order to reverse that I need raw data  
for  
analysis.

That is how I am handling it right now. I stream the output of the  
Correlate Access Code to a file sink. What is in that file though is  
data,  
not readable binary stream (or readable hex stream). What I want is  
tcpdump  
like output.

Jay R.  
Twitter: @jradcliffe02  
E-Mail: removed\_email\_address@domain.invalid  
LinkedIn + Resume: [http://www.linkedin.com/in/jradcliffe02](http://www.linkedin.com/in/jradcliffe02)

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 6:16pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/9 "2014-04-30T18:16:33Z")

</div>

Jay,

As it turns out I am working on an out-of-tree module to work with the  
CC1101, which I think I’ll be able to release. The number of possible  
formats for the frame are relatively few if you know they are using CRC  
and  
you know the packets aren’t fixed length. (use\_sequence\_number?,  
use\_address\_field?). By definition, we know there will be length field  
since these are not fixed length packets. It would probably just make  
sense to test the handful of options until CRC passes.

Of course, this changes if the device isn’t taking advantage of CC1101s  
packet handling functionality, and instead the MCU is providing more  
than  
just the “payload”. In such a case, there is potentially larger feature  
space for the frame.

I’ll let you know about the CC1101 OOT.

-John

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 6:40pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/10 "2014-04-30T18:40:21Z")

</div>

Cool! In case either of you doesn’t have this yet, here is an  
implementation of the CC11xx whitening algorithm:

# XOR the output of this with a packet

def whitening(length):  
lfsr = 0x1ff  
white = 0  
for i in range(length):  
white \<\<= 8  
white |= (lfsr & 0xff)  
lfsr = advance(lfsr, 8)  
return white

Not all implementations use the whitening feature, but I once reversed  
one that did. The algorithm is described in the data sheet, but the  
description is lacking a couple details that I had to figure out.

Mike

On Wed, Apr 30, 2014 at 09:15:11AM -0700, John M. wrote:

> On Wed, Apr 30, 2014 at 8:22 AM, Jay R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:
> 
> > not readable binary stream (or readable hex stream). What I want is tcpdump
> > 
> > > Jay,  
> > > -John
> > > 
> > > > just when a signal is over a certain strength. In a perfect world, I would
> > > > 
> > > > > is relatively straight-forward. If you are using the (tag) version of that
> > > > > 
> > > > > > demodulation portion of handling a signal. Currently I am taking that data

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 5:59pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/11 "2014-04-30T17:59:26Z")

</div>

My workflow in this case is to dump the output of Correlate Access Code  
to a file and then write small Python programs to read that file. Yes,  
the tools within GNU Radio for handling this kind of thing are getting  
better, but they still haven’t been as useful (to me) as a few lines of  
Python here and there for reverse engineering packet formats.

An example of a framework I might start with:

import struct

maxbytes = 255  
data = open(‘/tmp/bits’).read()  
symbols = struct.unpack(‘1B’\*len(data), data)  
pkts =

# extract an integer value from bitstream

def extract(start, len, bits):  
val = 0  
for i in range(start, start + len):  
val \<\<= 1  
val += (bits[i] & 1)  
return val

# make a big integer out of a packet’s bits and display it in hex

def decode\_packet(start):  
print(“decoding packet %d” % (len(pkts)))  
pkts.append(extract(start, maxbytes\*8, symbols)  
hexformat = “%0” + str(maxbytes \* 2) + “x”  
print(hexformat % pkts[len(pkts) - 1])

# look for correlations flagged by correlate\_access\_code\_bb (second bit

set)  
for i in range(len(symbols) - maxbytes\*8):  
if symbols[i] & 2:  
print  
decode\_packet(i)

You could modify this to print in binary instead of hex. If you want to  
display the preamble and/or sync word or not, you can subtract a fixed  
value from the frame start index. From there I start adding functions  
as I figure things out. For example: de-whitening, extracting length  
fields (and using that length instead of maxbytes), manchester encoding,  
error correction, xor packets against each other for differential  
analysis, etc.

Mike

On Wed, Apr 30, 2014 at 09:22:54AM -0600, Jay R. wrote:

> not readable binary stream (or readable hex stream). What I want is tcpdump
> 
> > Jay,
> > 
> > > like to have “Binary Slicer” → “File Sink” where the file contents are the  
> > > On Sun, Apr 27, 2014 at 9:28 PM, John M.  
> > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:
> > > 
> > > > block, you simply need to look for the presence of that tag to delineate
> > > > 
> > > > > sink. This produces a data file. I didn’t know if someone could tell me a  
> > > > > Jay R.

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 6:45pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/12 "2014-04-30T18:45:16Z")

</div>

Oops. I forgot part of it:

def advance(lfsr, num):  
for i in range(num):  
nextbit = (lfsr & 1) ^ ((lfsr \>\> 5) & 1)  
lfsr \>\>= 1  
lfsr |= (nextbit \<\< 8)  
return lfsr

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [April 30, 2014, 6:42pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/13 "2014-04-30T18:42:47Z")

</div>

Of course - I forgot whitening as a nother parameter to be tried.  
Thanks!

-John

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [May 2, 2014, 2:53pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/14 "2014-05-02T14:53:04Z")

</div>

Hi,

By chance I am also working on an OOT module for a CC1100-based device.  
I started out with a Python version as Michael also suggested, but now I  
am migrating it to C++. I actually plan working on it during the EU  
Hackfest next week in Karlsruhe.

John, Jay, perhaps we can create a single module for this as those chips  
are very similar, something like gr-cc110x perhaps.

Cheers,  
Andre

---

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**Author:** ![jay](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ed8c4c/32.png) [@jay](https://www.ruby-forum.com/u/jay)\
**Post date:** [May 24, 2014, 6:27pm UTC](https://www.ruby-forum.com/t/post-binary-slicer-question/240727/15 "2014-05-24T18:27:07Z")

</div>

Hi,

as I have mentioned a few weeks ago I was working on a GR module that  
can be used for receiving and decoding messages sent from TI CC11xx  
based devices.

I’ve now pushed a first version of it to my github repo [1]. It features  
a 2-FSK receiver entirely built from stock GR blocks and a deframer with  
a message output port that also does de-whitening and CRC checking.

Hope anybody else has use for it.

Cheers  
Andre

[1] [GitHub - andrepuschmann/gr-cc11xx: GNU Radio OOT module for communicating with TI CC11xx based devices](https://github.com/andrepuschmann/gr-cc11xx)