Re: [libusb] Issue with raspberry pi and libusb_bulk_transfer if buffer size is too big

[Tim R. <ti...@pr...>]

On Jul 24, 2019, at 1:28 PM, David Levy <dav...@le...> wrote:
> 
> We have an application that use libusb to communicate with a sensor. On windows and linux x86/x64 it works fine, however, when using a raspberry pi 3, I have a weird issue.
> ... 
> We can see that we still have the 0x1c8, and I checked that the data inside is correct. But the other paquets (0x10) are incorrect.
>   
> Is there any reason that a size > 0x4000 is problematic?

Yes, actually, although it’s not clear how it leads to this problem.

A USB device is never told how large the buffer is.  It’s just given a “go” signal, and it is entitled to send any amount up to and including the max packet size.  Thus, the buffer for a USB transfer must always be an even multiple of the endpoint’s max packet size.  For a high speed device, that means a multiple of 512.
— 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.