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

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

David Levy wrote:
>> Your description seemed to say that all of the returned packets were less than the full packet size.  Is that true?  If so, there's really no reason to have your buffer be so large. A transfer is completed as soon as there is a packet shorter than the max packet size.  If they're all less than 64 bytes, then you can make the buffer 64 bytes.
> The maximum possible packet the device can send is 0x4000 bytes (if the device streams a different kind of data). So if I set the buffer size to 0x4000 I can have everything working. But I'd like to understand why

The maximum TRANSFER the device can send is 0x4000 bytes.  The maximum 
PACKET is 64 bytes.  On the wire, it's all just packets, 64 bytes in 
this case.  In the software protocol, a "transfer" continues until the 
buffer is filled, or a packet shorter than the maximum is sent.

Did you write the device firmware?  Do you send a short packet when a 
transfer is complete?

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.