Re: [pyusb-users] pyUSB - delayed sending to the device? / Ubuntu 19.10

[Xiaofan C. <xia...@gm...>]

On Sun, Jan 31, 2021 at 9:37 PM Kevin Grant <ele...@my...> wrote:
>
> On 2021-01-31 12:58, Kevin Grant wrote:
>
> > Hello,
> >
> > I am re-using a subject line from the mailing list archive, by user
> > Marcin, in an attempt to append to that thread.
> >
> > https://sourceforge.net/p/pyusb/mailman/pyusb-users/thread/15e9538f-386f-a637-ce2b-5eea3d04bd76%40gmail.com/
> >
> > I had a simlar issue recently with a simple test application which
> > opened a device and sent some OUT packets (to 512 size endpoint) thus:
> >
> > ..open device..
> > for i in range(n):
> > dev.write(2,bytearray(os.urandom(512))
> > ..close device..
> >
> > On windows, this worked fine for any 'n' but on Linux only even 'n'
> > worked correctly. For odd 'n' one packet was always dropped/stuck.
> > As Marcin suggested, ending with dev.reset() seemed to flush this stuck
> > packet and fixed the issue.
> > But using reset in this way seems wrong.
> > After opening the device calling
> > dev.clear_halt(2)
> > Seemed to fix the issue.
> >
> > Regards
> > Kevin
>
> Ah, perhaps a better solution is to write a zero-length packet to
> signify end of data stream...
>
> ..open device..
> for i in range(n):
>    dev.write(2,bytearray(os.urandom(512))
>
> dev.write(0x02, bytearray()) #ZLP end of data
>
> ..close device..
>

It may be that Linux and Windows may handle the things a bit differently.
Still ZLP may help for bulk endpoint.
https://www.beyondlogic.org/usbnutshell/usb4.shtml

-- 
Xiaofan