On Mon, Aug 18, 2008 at 7:54 PM, George Nychis <[EMAIL PROTECTED]> wrote: > 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.
Yes. There are issues, but enjoy traveling. > 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. Just to clarify the situation - the current packet_builder is hooked up after the sample buffers so as it is building one packet, it cannot build another. That is why when 2 channels were used, they would be received 270+ samples from each other as that is around the time it takes to generate the full packet. Moreover, the timestamp actually had nothing to do with the actual sample time - just the time the packet was built. Therefore, no 2 packets could have the same timestamp (which should be possible). > 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? Correct. Multiple packet_builders which allow for proper timestamping along with some artiber to get the packets out to the FX2. > Two major issues we're looking at solving: timestamping the first sample > (for real), and a non-jumpy timestamp. Yep! > Thanks! > George No problem. Brian _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
