Re: [Libusb-devel] Bulk transfer perfromance

[Michael P. <mic...@gm...>]

2:  A) With a totally different project (i.e., not libusb), I've found that
my code can behave funny over an ssh connection if I fail to make stdout
nonblocking (fcntl(fileno(stdout), F_SETFL, oldflags | O_NONBLOCK)) when the
ssh connection is likely to drop out.  B) Locally, on older computers, I've
noticed that certain very long displays which I don't care about can be sped
up by temporarily switching to a different virtual console.

Both of these indicate you may be slowed down in some cases.  You might just
try it and print your own (condensed) error info instead, if possible.  Does
the display appear to lag?


1:  I don't know, but the frames are scheduled every 1 ms.  I've heard
something about doing async transfers, and queueing multiple transfers up to
increase the likelihood you're scheduled on EVERY 1ms frame.  You can
theoretically schedule quite a few 64-byte packets in that 1ms (though not
quite 12Mbps).  I've never tried it, but you might look there.  The bulk
transfers are not guaranteed BW afaik, so they might suffer from high
traffic.

Michael


-----Original Message-----
From: Rick Lamanna [mailto:Ric...@mc...]
Sent: Friday, July 24, 2009 9:55 AM
To: lib...@li...
Subject: [Libusb-devel] Bulk transfer perfromance


Hello,

I have a couple of questions on bulk transfers.

1.       I have a device that scans data at various clock speeds.
Unfortunately, the device has a very small buffer. At the device's maximum
rate, the buffer fills up in 2.5 mS. I read data from the buffer using bulk
transfers. The device has a max packet size of 64 bytes. Can I expect to
read data from the device's buffer fast enough using Libusb so that I don't
lose data? (actually the device will go into an overrun state if I don't
read fast enough)
2.       Does setting the Libusb debug level to 3 impact the performance of
doing bulk transfers? I testing the throughput of my device - should I set
the debug level to 0?
Thanks

Rick L