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

[Kevin G. <ele...@my...>]

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..

Regards
Kevin