Re: [Pyusb-users] HID device in OS X

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

Hi again,

short update: I just managed to make it work.
For reasons I don't understand it was sufficient to add a read  
request directly after the write. So now my methods are like this:

def sendCommand(self, cmd):
	buffer = ([0,] * 2)
	buffer[0] = cmd
	buffer[1] = 0
		
	self.write(buffer)
	return self.read(64)
	
def write(self, buffer, timeout = 100):
	return self.handle.interruptWrite(self.ep_out.address, buffer, timeout)

The device is reacting and I can finally go home ;-)


But if you have any recommendations or critic on the way I do it, it  
would interest me anyway!

best regards,
Ralf

Am 10.12.2008 um 17:50 schrieb Ralf Baumbach:

> 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