Re: [Discuss-gnuradio] FX2 firmware

[Dominik Auras]

Hi Eric,

Thanks for the answer.

> It's hard to say.  If you've got a logic analyzer you can instrument
> the inner loop of the firmware and see if that's the bottleneck or not.
Unfortunately, I don't have a access to a logic analyer :(

However, I made progress that I am going to share once it is tested and 
cleaned up.

Short summary:
When doing RX only, I am at 45 Mb/s (yes! decim=6 works without 
underruns). On the TX side, I can't get above 32.7 Mb/s. Now I suspect 
that this is a host side bottleneck. On the FX2, if using only one 
direction, I am setting the GPIF to loop infinitely. With GPIFABORT=0xFF 
to switch if the state changes. Hence there is no main loop left that 
could be a bottleneck. The TX state machine now consists of 2 states, 
where state one is the idle state, and state 2 transferring data (one 
word per clock, as before). The 8051 core is completely out of the data 
path. (Auto commit etc.)
Same for RX, except that a few more states were needed.

When RX and TX are needed, the firmware is still faster, though the same 
TX bottleneck appears (which is, of course, no big problem because we 
already share USB bandwidth).

Do you have, maybe, an idea why TX bandwidth is limited? Interestingly 
enough, 32.7 Mb/s is the limit on my computer and my notebook. Of 
course, I made the tx loop on the host as short as possible, set 
SCHED_FIFO and rtprio to 49, and played with fusb_nblock/size etc.

Dominik