Re: [Discuss-gnuradio] problem with start/end of burst inband FPGA code

[Jeff Brower]

George-

> We'd greatly appreciate any help, thanks!

I started to take a look at your Verilog code and see if I could find 
something, then
stopped.  Can you repost it with correct indent/alignment?  It's hard to read 
when
you've got something like this:


                    if  (fifodata[`STARTOFBURST] == 1  
                       && fifodata[`ENDOFBURST] == 1) 
                       burst <= 0; 
                    else if (fifodata[`STARTOFBURST] == 1) 
                        burst <= 1; 
                    else if (fifodata[`ENDOFBURST] == 1) 
                        burst <= 0; 
                     
                                    //Check trash 
                                    if (trash == 1 && fifodata[`STARTOFBURST] 
== 0) 
                                    begin 
                                            trash <= 1; 
                                            skip <= 1; 
                                            reader_state <= IDLE; 
                                    end 
                                    else 
                                    begin  
                            payload_len <= fifodata[`PAYLOAD] ; 
                            read_len <= 0; 
                        reader_state <= TIMESTAMP;    
                        rdreq <= 1; 
                                    end 
                end 

which should be:

                    if  (fifodata[`STARTOFBURST] == 1 && fifodata[`ENDOFBURST] 
== 1) 
                       burst <= 0; 
                    else if (fifodata[`STARTOFBURST] == 1) 
                       burst <= 1; 
                    else if (fifodata[`ENDOFBURST] == 1) 
                       burst <= 0; 
                     
                  //Check trash 
                    if (trash == 1 && fifodata[`STARTOFBURST] == 0) 
                    begin 
                       trash <= 1; 
                       skip <= 1; 
                       reader_state <= IDLE; 
                    end 
                    else 
                    begin  
                       payload_len <= fifodata[`PAYLOAD] ; 
                       read_len <= 0; 
                       reader_state <= TIMESTAMP;    
                       rdreq <= 1; 
                   end 

Maybe one of your guys is using tabs and another isn't, or something like that. 
 If
so it might help to establish some basic source code rules for a multi-person
project.

-Jeff


George Nychis wrote:
> 
> Hey all,
> 
> We're looking for someone to look over our shoulder on an inband FPGA
> problem we've been stuck on for a couple days now.
> 
> The problem is that we never had code that throws out additional packets
> in a burst if the initial packet had a timestamp that expired.  When an
> m-block message is fragmented into multiple USB packets, the packets are
> considered a single burst, where the first packet has the start of burst
> flag set and the last packet has the end of burst flag set.  The first
> packet has the timestamp set to the desired timestamp, and each
> additional packet in the burst is given the 'NOW' timestamp.
> 
> The problem was that our code would throw away the first packet if the
> timestamp expired, but the additional packets in the burst had a
> timestamp of 'NOW' so they would be sent... but they shouldn't be since
> they are part of an 'expired' burst.
> 
> Ok, so on to the code:
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v
> 
> The logic needs to be "if the packet with the start of burst flag was
> thrown away, throw away all packets until we see the end of burst flag."
> 
> If we see the start of burst flag, we set 'burst' to be 1.
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v#L97
> 
> If the timestamp has expired on the packet, set 'trash' to 1, and 'skip'
> set to 1:
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v#L148
> 
> Finally, if we get a packet that does not have start of burst set, it
> *must* be an intermediate packet or the last packet in a burst... either
> way it does not matter.  If 'trash' is set to 1, we want to skip it:
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v#L106
> 
> If we see the end of burst flag, 'burst' is reset:
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v#L102
> 
> If the next packet has a correct timestamp, we set trash back to 0.  We
> could just set trash to 0 when end of burst is read, but it doesn't
> really matter:
> http://gnuradio.org/trac/browser/gnuradio/branches/developers/zhuochen/burst/usrp/fpga/inband_lib/chan_fifo_reader.v#L137
> 
> So... as you can guess, this doesn't work.  This hasn't been our only
> attempt.  We've trashed the code and re-written it a couple different
> times with no success.
> 
> To test this we've been setting all packets to have a timestamp of 0.
> This means we should get no sine wave on an oscope when transmitting,
> regardless of the number of packet sin the burst.  However, we see
> chunks of the wave here and there when the number of packets in the
> burst is greater than 1.  If we set it so that a single m-block message
> only creates 1 USB packet, it works... everything is thrown away.
> 
> We'd greatly appreciate any help, thanks!
> 
> - George, Leo