Re: [Discuss-gnuradio] inband timestamp issues

[George Nychis]

Okay, more on topic with the original problem: the timestamp issues. 
The problem that Steve noticed was that the timestamps jump.

Brian and I wrote a testbench for this and found that the timestamp 
actually does not really correspond to the first sample (per the design 
doc), and not quite the last sample either... but closer to the last 
sample.  So... this is also an issue.  But I think that fixing both will 
be along the same lines.

Brian, can you verify all of this?  I wanted to mail it to the list for 
documentation, and so when Leo gets back he can read it.  I've been 
slammed with traveling in August and wont be back for another week.

So what we suspect is that the FX2 will keep up for a while, and then 
get suspended/busy/something for a while which causes it to stop 
building packets.  The samples are still being buffered, but the actual 
packets are not being built (causing a jump).

In this time, nothing becomes full and dropped, which is why an underrun 
is not reported.  All samples make it through to the host.

Brian's solution was the following:
 - connect the input of packet_builder to be the output of the halfband 
filter (for each channel)
 - output the previous to an asynchronous FIFO driven by rxclk
 - have a FIFO arbiter on the output running off usbclk
 - FIFO arbiter cycles through the FIFOs for a packet
 - if packet is available, connect FIFO to FX2 and wait for FX2 to parse

Does that sound about right, Brian?

Two major issues we're looking at solving: timestamping the first sample 
(for real), and a non-jumpy timestamp.

Thanks!
George