Re: [Discuss-gnuradio] custom work function gets into an endless loop
The dvb_bbheader_bb_impl.cc module in gr-dtv also uses set_output_multiple(). Ron On 09/28/2015 08:36 PM, Kolya wrote: Hi Martin and Sylvain, I obviously didn't understand the forecast function properly but with your help it works now. I tried both: set_output_multiple & a correct forecast() and set_output_multiple & set_relative_rate both approaches worked as expected :) What threw me off was that I had based my forecast on the forecast function in gr-dtv's dvb_bbheader_bb_impl.cc and in that example it seems to work. I also appreciate the pointer to the logging infrastructure and I will adopt that too. The crc32_bb is next on the list of files to dissect and learn from. That is good stuff! This is a great mailing list. Thanks so much for your help. - Kolya ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] custom work function gets into an endless loop
Hi Martin and Sylvain, I obviously didn't understand the forecast function properly but with your help it works now. I tried both: set_output_multiple & a correct forecast() and set_output_multiple & set_relative_rate both approaches worked as expected :) What threw me off was that I had based my forecast on the forecast function in gr-dtv's dvb_bbheader_bb_impl.cc and in that example it seems to work. I also appreciate the pointer to the logging infrastructure and I will adopt that too. The crc32_bb is next on the list of files to dissect and learn from. That is good stuff! This is a great mailing list. Thanks so much for your help. - Kolya -- View this message in context: http://gnuradio.4.n7.nabble.com/custom-work-function-gets-into-an-endless-loop-tp56304p56323.html Sent from the GnuRadio mailing list archive at Nabble.com. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] custom work function gets into an endless loop
> /void
> bbframer_bb_impl::forecast (int noutput_items, gr_vector_int
> _items_required)
> {
> ninput_items_required[0] = ((noutput_items - 32) / 8); // 32 bit
> postamble
> }/
You should make sure forecast can never return <0 or even ==0 numbers.
Returning 0 means you can produce output without input and the only
valid case for it is either a 'source' block, or if you _know_ that
you have currently buffered data and you can produce output without
any further inputs.
Cheers,
Sylvain
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Re: [Discuss-gnuradio] custom work function gets into an endless loop
On 27.09.2015 15:25, Kolya wrote:
> Hi,
>
> I'm trying to build a custom block that takes in a stream of input samples
> and simply adds a postamble of 32bits every 352 bits. The package structure
> is illustrated below (payload_bits = msg_bits+postamble_bits):
> ---
> | msg_bits = 352 | postamble_bits = 32 |
> ---
>
> For some reason the code below gets into an endless loop when I run it
> through a test and stimulate it with a non-repeating vector source. The
> debug printf statements show that the loop keeps iterating even without
> input.
> I derived from gr_block because the number of output samples is higher than
I'm guessing you mean gr::block? If so, that's the correct choice.
> }
> #ifdef VERBOSE
> printf(">>> offset= %d\n",out_offset);
> printf(">>> consumed= %d\n",consumed);
> #endif
FYI, we have a great logging infrastructure for these kinds of things,
see http://gnuradio.org/doc/doxygen/page_logger.html.
> this->consume_each(consumed);
> return out_offset;
> }/
>
> I also overrode the forecast function to account for the fact that fewer
> input samples are needed than output samples are produced:
>
> /void
> bbframer_bb_impl::forecast (int noutput_items, gr_vector_int
> _items_required)
> {
> ninput_items_required[0] = ((noutput_items - 32) / 8); // 32 bit
> postamble
> }/
There's several issues here. First, your math is broken; you want
ninput_items_required to always be a positive, non-zero number which
you're not checking. Say it's 0, then that means it's fine to call your
work function with no input. What you want is something like
'(noutput_items / 47) * 44.
Second, you don't necessarily need forecast. If your packet size is
always the same, I recommend using set_output_multiple and
relative_rate. Or you can even use tagged streams, check out crc32_bb
which does pretty much the same as your block, albeit at varying packet
lengths.
Cheers,
M
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[Discuss-gnuradio] custom work function gets into an endless loop
Hi,
I'm trying to build a custom block that takes in a stream of input samples
and simply adds a postamble of 32bits every 352 bits. The package structure
is illustrated below (payload_bits = msg_bits+postamble_bits):
---
| msg_bits = 352 | postamble_bits = 32 |
---
For some reason the code below gets into an endless loop when I run it
through a test and stimulate it with a non-repeating vector source. The
debug printf statements show that the loop keeps iterating even without
input.
I derived from gr_block because the number of output samples is higher than
the number of input samples and the work function is shown below:
/void bbframer_bb_impl::general_work(int noutput_items,
gr_vector_int _items,
gr_vector_const_void_star _items,
gr_vector_void_star _items)
{
const unsigned char *in = (const unsigned char *) input_items[0];
unsigned char *out = (unsigned char *) output_items[0];
int out_offset = 0;
int consumed = 0;
for (int i = 0; i < noutput_items; i += (int)(payload_bits/8)) {
for (int j = 0; j < (int)(msg_bits / 8); j++) { //
Input index loop
(byte-index)
out[out_offset++]=in[consumed++];
}
// now add add postamble
out[out_offset++]=0x00;
out[out_offset++]=0x01;
out[out_offset++]=0x02;
out[out_offset++]=0x03;
}
#ifdef VERBOSE
printf(">>> offset= %d\n",out_offset);
printf(">>> consumed= %d\n",consumed);
#endif
this->consume_each(consumed);
return out_offset;
}/
I also overrode the forecast function to account for the fact that fewer
input samples are needed than output samples are produced:
/void
bbframer_bb_impl::forecast (int noutput_items, gr_vector_int
_items_required)
{
ninput_items_required[0] = ((noutput_items - 32) / 8); // 32 bit
postamble
}/
Any feedback would be greatly appreciated.
- Kolya
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