Re: [Libusbx-devel] libusb_control_transfer() stalls

[Tim R. <ti...@pr...>]

Markus wrote:
> As of now, I can read and write memory by using vendor request
> control transfers. According to the manufacturer this is the way 
> to go for firmware dump and download.

That's a common mechanism.

 
> wValue (LSW) and wIndex (MSW) make up the address offset to write 
> the data to within device memory.

Are you sure you have the ordering correct?  (It probably is, because
that lets those two fields  be treated as a single little-endian dword.)

 
> In both cases (r/w), the maximum value for wValue is 0x4000, after
> that libusb_control_transfer() returns pipe errors. As it is
> possible with the original tool to write beyond this address, I
> suspect it's not the device that produces the stall.

What is the actual error code you get from WinUSB?  If the error really
is a stall, then has to come from the device.  What is the
bmRequestType?  Is it a vendor request to the device?  Would you mind
showing us the code?


> As I don't have any known-good device where I could meaningfully
> test a control transfer with wValue > 0x4000, I'd also be happy 
> for any hint towards how to reproduce this behaviour.

I have certainly done vendor device requests with wValue larger than 0x4000.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.