Read from bulk end point

[Luca Pizzamiglio]

Hi,

thanks HPS, yes, the buffer size works well.
It was strange, because for other endpoints I don't see this kind of 
behavior.
BTW now the problem is solved.
Thanks again

Luca

On 06/27/11 11:19, Hans Petter Selasky wrote:
> On Monday 27 June 2011 10:43:03 Luca Pizzamiglio wrote:
>> Hi USB list,
>>
>> I've a little problem, but I'm not able to find a solution...
>> I've a generic custom USB device with several end points.
>> One of them (a bulk one) is read periodically (polled, 64 byte) every
>> second. There was some time inconsistencies, so I checked the USB
>> traffic with a sniffer, and I discovered that transactions are compacted
>> at the start of the loop in a block of 64 read (64 byte * 64 msg = 4096
>> byte). In other words, on the bus the first read is followed immediately
>> by the next 63 read.
>>
>> I guess that this is a pre-fetch optimization for BULK end points. How
>> can I disable this optimization for this end point? How can I come back
>> to a more "real-time" behavior? I tried to play with open() flags
>> (O_NONBLOCK, O_DIRECT) without luck.
>>
>> Using FreeBSD 7 with HPS stack, this behavior didn't happen. Every read
>> consists in 1 read on the bus and everything is fine.
>>
>> Thanks in advance!
>>
>> Luca
>
> There is an IOCTL to set the RX and TX buffer sizes. Please use that. See
> dev/usb/usb_ioctl.h. The default is more than one full packet.
>
> --HPS