[SOLVED]BULK_BUFFER_SIZE

Hello Gianluca,

Note that the maximum size of a Bulk transfer is 64 bytes for LS/FS and 512 bytes for HS. So it is up to your application to decide what the size you want to put out.

Regards
Amit

Thanks Amit, just for me to understand more, if I want to send...let's say 1000 bytes....and I have a BULK_BUFFER_SIZE of 64 bytes...the driver with manage to pack my 1000bytes in blocks of 64 or I can't send more that 64 bytes for transit?

Hello Gianluca

The packet will be sent in the MAX Packet Size chunks with the last transfer sent as is with remainder packet size or terminated with a Zero Data Packet

Regards
Amit

ok, so...let me explain the situation.
I wanted to send 400bytes for transfer....and I set BULK_BUFFER_SIZE to 1024. I understand now that it is not ok ...but the SW works pretty well with few errors...
Now after your answer I set BULK_BUFFER_SIZE to 64 (I use fullspeed USB from TIVA). the result is LIBUSB_TRANSFER_ERROR every time the HOST asks the data... If I can't send more than 64/2 = 32 bytes per transfer..then I can't send more that 1frame of data per 1ms which is very very slow for my application.

Hello Gianluca

My bad. Since the size of the data is 400 bytes, the buffer size must be twice the size of the Max Size USB Packet.

Regards
Amit

thanks, that is 1 point closed :-) . I really appreciate your support.