Hi!
In short: How should a udc driver handle a situation when the host sends
more data than req.length in the receiving OUT request? What
should be reported to the gadget driver? What should be done with the
excess data?
Currently the gr_udc driver does not accept OUT requests if req.length
is not a multiple of ep.maxpacket. This is because the hardware cannot
be told to write smaller data sizes than ep.maxpacket. (This works fine
for mass storage for instance that makes sure to supply request buffers
that are even multiples of ep.maxpacket, but not all gadget drivers do
this.)
I am looking into lifting this limitation by using an internal buffer in
gr_udc.c in that is used instead of end of the req.buf that is
not (necessarily) a full multiple of ep.maxpacket and then copy received
data from the internal buffer to the request buffer.
The problem is that the gr_udc driver then can end up in the situation
where it receives more data than req.length (e.g. a full sized packet of
size ep.maxpacket). What should be done in the udc driver in this case?
What should be reported to the gadget driver? What should be done with
the excess data?
Best regards,
Andreas Larsson
Software Engineer
Aeroflex Gaisler AB
Aeroflex Microelectronic Solutions – HiRel
Kungsgatan 12
SE-411 19 Gothenburg, Sweden
Phone: +46 31 7758669
andreas@xxxxxxxxxxx
www.Aeroflex.com/Gaisler
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