Re: [libusb] Issue with Bulk Transfer in Raspberry PI

[Ludovic R. <lud...@gm...>]

2013/12/29 Abhishek Madaan <abm...@ya...>:
> Hi,

Hello,

>    We are developing a camera to talk with Raspberry Pi. The issue we are
> facing is that sometimes we are not able to receive full frame. We are using
> the bulk mode transfer. The camera resolution is 640x480 with 2 bits per
> pixel. So I am calling the filling the bulk loop with an array of unsigned
> short 640x480 with a size of 614400. The problem I am receiving that
> sometimes I able to only get 606208 bytes before the bulk transfer times
> out. Is the speed of the CPU matters in the transfer? In the firmware level,
> we receive a control transfer command before the camera start sending the
> data to the host. I submit the bulk transfer before I submit the control
> transfer to make sure the host is receiving data before the device can send
> the data. At the firmware level, we are using end point 2 with Quad
> buffering with packsize = 1024. We are using Cypress GPIF to receive the
> frame from the camera. We are Auto In mode with  512 bytes. Here’s my code
> snippet. Can anyone explain me what might be different reasons that i am not
> able to receive the full frame? Is Raspberry PI CPU is too slow? If yes, but
> how it is interfering with IO? Why I receive full frames sometimes and
> sometimes not? Is there any way to speed up using the same processor.  Any
> help on this matter would be really appreciated. Thanks

It looks like the Raspberry Pi USB hardware is not reliable in USB 2.0
mode and lose USB packets.
See http://www.yoctopuce.com/EN/article/the-quest-for-the-ideal-mini-pc

Bye

-- 
 Dr. Ludovic Rousseau