Re: Different input/output rate

GNU Radio
1

Eric B. wrote:

isn’t
Basically you subclass gr_block, provide forecast and general_work

Thanks, I think I am starting to figure thinks out.

When referring to gr_simple_framer (which I am using as an example), may
you
please help me understand the processing part (lines 76 to 89 in the .cc
file)?

So, we are adding a synchro sequence at the beginning of a frame of
‘payload_bytesize’ bytes. I suppose lines 79 to 87 in the while loop add
the
synchro sequence and the sequence number. Line 89 copies
‘payload_bytesize’
bytes of input data to output stream after de synchro sequence. But why
write 0x55 ‘noutput_items’ bytes to ‘out’ (Line 76)?

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2

I am trying to extract data from a Turbo Code signal. My block’s input
is the
signal with synchro sequences between frames. The block processes this
input
in order to drop FEC bytes and send only useful data on the ouput. The
problem is I need a complete frame to process data correctly so any
incomplete frame at the start or end of the capture is to be ignored. I
don’t know how to handle this when implementing the forecast method.

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3

On Mon, Jul 21, 2008 at 02:23:55AM -0700, irene159 wrote:

http://www.gnu.org/software/gnuradio/doc/howto-write-a-block.html
When referring to gr_simple_framer (which I am using as an example), may you
please help me understand the processing part (lines 76 to 89 in the .cc
file)?

So, we are adding a synchro sequence at the beginning of a frame of
‘payload_bytesize’ bytes. I suppose lines 79 to 87 in the while loop add the
synchro sequence end the sequence number. Line 89 copies ‘payload_bytesize’
bytes of input data to output stream after de synchro sequence. But why
write 0x55 ‘noutput_items’ bytes to ‘out’ ?

This could be cleaned up. It provides the tail padding (and at one
time in the development, there was also a 0x55 preamble, and this
handled it). We eventually moved on and changed how we handled the
creation of the framing. It’s now done in python. See pkt.py.

Eric

4

On Mon, Jul 21, 2008 at 06:04:54AM -0700, irene159 wrote:

I am trying to extract data from a Turbo Code signal. My block’s input is the
signal with synchro sequences between frames. The block processes this input
in order to drop FEC bytes and send only useful data on the ouput. The
problem is I need a complete frame to process data correctly so any
incomplete frame at the start or end of the capture is to be ignored. I
don’t know how to handle this when implementing the forecast method.

First off, do you know how to locate the beginning of the header in
your data? Does the header include the length of the frame?
You’ll need some kind of state machine…

Have you looked at how we handle this in
gnuradio-core/src/python/gnuradio/blks2impl/pkt.py in the demod_pkts
class?

Eric