[Pyusb-users] HID device in OS X

[Ralf B. <ral...@gm...>]

Hi,

I'm trying to talk with an eMagin Z800 HMD (HID device) via usb on OS  
X 10.4 (later also on linux).
The necessary information comes directly from the eMagin SDK, so that  
I know what commands the device is expecting. I also created an empty  
kext a while ago that keeps OS X of opening the device exclusively  
(though I don't know if it's important).

My problem is that there is no reaction from the device. For a start  
I try to put it in sleep and to wake it up, but obviously it doesn't  
work. I checked with another example that I wrote a while ago in C++  
(though I don't know C++, but I copied a lot of example code from  
Apples IOKit documentation) that is capable of doing what I want to  
do. So I checked and it's working, but it's not working when I have  
claimed the interface with PyUSB. I take this as a prove that the  
connection (via PyUSB) to the device is successfully established (I  
can also read from the device).

In the python script that I wrote I did basically the same as what  
happened in the C++ code. It's the same device, configuration,  
interface, endpoints ... everything should be the same.
But I cannot make it do what I want, so I think it will be just a  
lack of knowledge on my side. But it surprised me, that it doesn't  
work as I expected, given the fact that I even managed to make it  
work in C++ ;-)

Here is what I try to write to the interrupt endpoint:
buffer = ([0,] * 64)
buffer[0] = cmd
buffer[1] = 0
result = self.write(buffer)

cmd is on of:
cmdSleep		= 0x85
cmdWake		= 0x8A
cmdBrightness	= 0x88
(eMagin SDK)

The write method is taken from the usbprint.py sample of PyUSB, just  
a little bit adapted:
def write(self, buffer, timeout = 100):
	return self.handle.interruptWrite(self.ep_out.address, buffer, timeout)

ep_out is an endpoint object.

When I print out the result I see that 64 Bytes have been written.  
But there is no reaction from the device. No errors neither.
I'm not a great expert on python, usb or data types, so I hope  
there's something obvious that I'm missing.

If you need more information to be able to understand the problem, I  
will give it gladly on demand of course.

thanks for reading,
Ralf