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
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