Hi all,
I'm new to USB so I thought I'd dip my toe in
the water via usbfs. I'm trying to send a range
of buffer sizes using bulk transfers. When
submitting lots of very small buffers (64 byte
up to about 1k) I'm finding that the fastest
rate I can submit is about 325 per second.
Just to check that I was sure about the 3ms
delay being cause by the submit ioctl I did
something like this:
create 4000 small empty buffers/urbs OUT
for x 1 to 4000
{
ioctl(submit,buffer(x))
}
reap all and free all
I'm using a late-ish 2.4 kernel with UHCI
and setting the BULK_QUEUE flag.
I did try briefly with EHCI and it was quite
a bit faster (but not sure how much, will try
today) but my target may not have EHCI.
Is this likely to be performance limitation
of usbfs (forcing me to move to a kernel
module) or should I be able to call in from
user-land faster than that. i.e. should the
ioctl return faster than 3ms ?
Or is it some odd queuing or timing thing
inherent in UHCI?
TIA for and comments, Jason
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