High-speed transfers

Hans Petter Selasky hselasky at c2i.net
Sat Jul 1 15:31:04 UTC 2006

On Saturday 01 July 2006 16:24, Thierry Herbelot wrote:
> Le Saturday 1 July 2006 15:31, Hans Petter Selasky a écrit :
> > Yes, but don't forget high-speed USB transfers. They require larger
> > buffers. For example 1024 bytes for ULPT is too little. The interrupt
> > rate will be so high, that it is unrealistic to transfer 20MB/s using
> > 1024 byte interrupts. My rewritten ULPT now uses "2*(1<<17)" buffers.
> Hello,
> I wonder what kind of speed you are getting 

It depends much on the equipment you are using. For example I have a Brother 
USB 2.0, Laser Printer, postscript compatible, and if I were to guess, it 
eats something like 1MB/s. On the other hand I tested with an external USB 
2.0, 2.5" IDE adapter, and it transfers around 20MB/s.

> : I would like to see improvements for reads (and writes) on 
> standard endpoints, without having to resort to writing specific 
> drivers (using ugen on the standard FreeBSD USB stack).
> One goal would be to achieve something like 25 to 30 Mbytes/s, sustained,
> (finally getting to some interesting fraction of the peak USB2 data rate).

I don't think that will be a problem, as long as you use large enough buffers. 
A buffer of 1/50 th of the transfer rate should suffice, from my experience.


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