[iyonix-support] Iyonix driving K8055 board via USB - very slow?
- From: "Neil F" <faz@xxxxxxxxxxxxx>
- To: <iyonix-support@xxxxxxxxxxxxx>
- Date: Mon, 3 Aug 2009 11:09:09 +0100
Anyone fully familiar with the USB standard re sending bytes to a USB
1.1 device?
I'm using a heavily cut down, single-tasking version of Dave Higton's
USB prog for driving the Kellerman K8055 USB experimenter's board (as
sold by Maplin etc). I've been using it to drive stepper motors on an
old 8-bit robot arm but find there's an absolute upper limit to the
step speed that I can get the board to output, which seems to be
around 100Hz or 10ms per pulse.
This of course is too slow to get the arm moving at more than a crawl
- at least twice that pulse speed would be preferable. I have to
introduce delays in the coding to stop the Iyonix overrunning the card
ATM so clearly the hold up is not in the coding or processor speed.
I've seen references to the USB standard having a minimum update rate
of 10ms, which would account for the slow timing I'm getting. I
presume this means that while large packets of data can be sent to a
USB device at high speed (e.g. file transfers) there's an unavoidable
minimum overhead of 10ms for each packet. So if you want to send a
series of one-byte transfers (as I do) then the fastest transfer rate
possible is 100Hz.
Can anyone confirm this is the case, so I can stop trying to achieve
the impossible and start looking for other solutions?
-Neil F.
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