I wrote an email a while ago, but unfortunately I might have
missed any replies as a result of a mailbox issue (so thanks to
anyone who has replied, and sorry to have to post it again).
The issue is as follows. We are doing asynchronous (not
isochronous) communication to a device that has only 0.25 seconds of
buffer. Unfortunately, if we do not keep up with the device, we
cannot re-synchronize. Thus we must drain its buffer in time (it is
a pre-usb 2 device, so data traffic is not massive). The issue we
are seeing is that every so often, our time-stamps indicate that we
have delayed in our acquisition for more than 0.25 seconds. We can
also force this to happen more often if we load down the machine (as
one might expect). We currently load the requests on the bus to about
4-8 concurrent requests (to try to improve the situation).
The questions I have are:
1) Does a >0.25 delay sound reasonable to you guys? Ie, is it
possible that our usb request could be off the cpu for that much time?
2) After reading a bunch of past posts (by Fernando Urbina)
there seems to be an indication that if this indeed can occur, there
is little that we can do as it is an issue with how the primary
interrupt handler passes off events to the secondary handler. This
email was written back in 2002 though, and I was wondering if there
has been a work-around implemented in the meantime.
I would be happy to send current code samples if that would make
life easier. It just seems odd that we would really be off the
scheduler for that long.
Thanks for any help!!
Robert.
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