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Message
From: Dalton Marris<dmarris@c...>
Date: Mon Nov 22 23:14:32 CET 2004
Subject: [usb] Question regarding EP fifo full and NACK
I have created a new test for the USB 1.1 OpenCores testbench by
modifying the original "out0" task. I commented out the "fork" and
"join" lines (558 and 621) so that all of the data is written to the
fifo before anything is read out of it. With a fifo depth of 256, I
would expect the test to pass until the total number of bytes written to
the fifo is more than 256. With that said, when no_pack = 3 (actually 4
packets) and pl_size = 64, a total of 4 x 64 = 256 bytes will be written
to the fifo. This will fill the fifo, but just to it's maximum depth.
When this scenario occurs, the testbench fails, and I get the following
error message:
ERROR: ACK mismatch. Expected: d2, Got: 5a (2748140.0 ns)
I have verified that I am indeed getting a NACK back. Shouldn't I be
able to fill the fifo, as long as I don't try to overfill it, without
generating a NACK?
Regards,
Dalton
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