I've been working on adding USB1.1 (full speed) support to the USRP software/firmware so I can use it with a TI OSK board. I've been going back and forth with Matt on some issues and we are getting out of his area of expertise. Here is summary of progress to date.
After modifying the 8051 code I had the following behavior: When I compile the code for the OSK, I see two symbols transmitted, then dead air. Two symbols is 64 bytes (2 symbols x 8 sample/symbol x 4 bytes/sample), then there are 512 - 64 bytes of no signal. It feels like the 64 byte packets are read into a buffer of 512 bytes, where all the un-written bytes are zeros. It feels like somewhere in the USB chain, I send the 64 byte packet, then something reads the 64 bytes and zero pads the packet to 512 bytes. I suspect the FPGA tries to read 512 bytes from the FX2 chip, but that is only because this is the area of the code I least understand :) Matt suggested the following FPGA change, and I also chnaged a similar construct a few lines further on: http://gnuradio.utah.edu/trac/browser/gnuradio/trunk/usrp/fpga/sdr_lib/tx_buffer.v And look at line 94, you will see the test for "end of packet". write_count[8] goes high when we have put 256 elements (512 bytes) into the fifo. You would need to modify this to write_count[5] which will go high when 32 elements (64 bytes) have been put into the fifo. This results in: Well, it looks like data is coming out, but it looks like I get 64 bytes out, then there is a "hiccup" about 5 microseconds long. I am getting suspicious the OSK doesn't get the data on the USB bus fast enough. I'm still not entirely clear how the FX2 works. I am wondering if there is a way to let the buffers in the FX2 chip fill up more before the FPGA starts pulling data from the FX2. The OSK has a 192 MHz ARM9 processor. i have looked through the 8051 code for packet size dependencies and can't fins any I haven't aready tried to address. Does anyone else have any thoughts? Thanks, Philip _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
