Re: [Libusb-devel] Asynchronous reads with libusb1.0-windows backend

[Domien N. <dom...@gm...>]

Also, I'd like to add to my previous post that I am using bulk transfers 
with a timeout of 0.

> Hello all,
>
> I'm using the windows backend of libusb1.0, with the WinUSB driver, 
> and I'm trying to get better performance by submitting multiple bulk 
> transfers at once.
> My USB device is currently setup to send 4x512-byte packets and a 
> single 256-byte packet at once (and in that order) to the host, 
> followed by a delay of a second, and then followed by a single 
> 512-byte packet.
>
> On the host, I have submitted 16 asynchronous transfers at once, each 
> with a buffer capacity of 256K. Now my observations are as follows:
> I get one transfer callback with an actual_length of 2304 bytes, 
> followed by... nothing. My app just keeps idling and waiting for more 
> packets since it keeps printing a "Tick" message to the screen every 
> 100ms after handling libusb events. No errors are reported by libusb 
> whatsoever.
>
> My USB device also reports it has succesfully sent 2816 bytes, and for 
> those still listening it means that last 512-byte packet has gone into 
> limbo on the host as far as libusb (or WinUSB) is concerned.
> And, when I repeat the same test with a *synchronous* read, then 
> libusb returns successfully with *all* 2816 bytes. Pretty weird.
>
> So my question, is this the proper behavior of libusb?
> I was under the impression that the buffer length passed in the libusb 
> transfer was a maximum buffer size, and anything received smaller than 
> that will get passed back to the application too.
> I'd like to know how I can get that last 512-byte packet out with 
> libusb through asychronous transfers.
>
> Thanks in advance.
> Domien Nowicki.
>