USBView and WinUSB #2

[NicOfTime]

Hi, Jan.

I get repeated “access denied” (err 5) errors when trying to use WinUSB_Initialize to get a WinUSB handle to a device.  It’s possible that I may conflating the terms “device handle” and “device interface handle”.  I understand that, in some cases, the device handle and device interface handle may be the same thing – but, as a general rule, is WinUSB always communicating through device interface handles rather than device handles?  I can pass a device handle to CreateFile, and it returns “success”.  But when I pass the Windows handle from CreateFile to WinUSB_Initialize, I get “access denied”.  Is the system denying access because I’m trying to get a WinUSB handle via a device handle (which is valid) instead of a device interface handle (which is not really valid because I haven’t enumerated and passed them to Createfile yet)?

[Jan Axelson]

WinUSB_Initialize accepts a handle obtained by passing a device interface GUID to CreateFile.

Access denied might be due to the device already being opened by another driver.

What device are you trying to access?

[NicOfTime]

Hi, Jan.

Thanks so much for getting back with me.

I have a number of devices that are all supposed to abide by the USB-MIDI standard.  Two of them respond as expected using the winmm.dll USB-MIDI API (midiOutGetNumDevs() / midiOutGetDevCapsA / etc).  I can find and control these devices programmatically (with the MIDI functions) without a problem.

Some MIDI devices aren’t detected through those functions – the MIDI functions appear to filter out devices that don’t have a MIDI-streaming interface.

Even if they don’t stream MIDI, these devices will still respond to standard MIDI program and control change information through a USB connection – but only if I can get a handle to them.  I can talk to them through a hardware USB-MIDI interface (using the round 5-pin DIN connector cables), but those kinds of interfaces are giving way to USB-MIDI (much faster, more versatile interface).  The MIDI-specific API is becoming more and more obsolete – this is not been a priority for Microsoft, it hasn’t been updated in over a decade.

Since the MIDI-specific API doesn’t work, I have to take another approach.

I’ve successfully found the devices by feeding a suitable class ID to SetupDiGetClassDevs; I used SetupDiEnumDeviceInterfaces and SetupDiGetDeviceInterfaceDetail to get the device instance ID; I fed the device instance ID to CreateFile to get a Windows handle, then used that Windows handle with WinUSB_Initialize to get a WinUSB handle.  And this always fails with “access denied”, even when I know I’m feeding the intended device instance ID into those SetupDi functions.

So I’m guessing that I should be talking to specific interface ID’s in the device, not the device ID itself.  With a bit of trial and error, I can find the interface that will execute standard MIDI commands – for some devices, this has been through an interface labeled “AUDIO”.  My question had to do with a possible conceptual misunderstanding on my part -- that maybe communication links should be with interfaces rather than devices. (?)

[Jan Axelson]

WinUsb_Initialize uses the first (default) interface on the device:

http://msdn.microsoft.com/en-us/library/windows/hardware/ff540277%28v=vs.85%29.aspx

So I think the MIDI interface needs to be interface 0.

If the device is already installed using another driver, WinUSB might be unable to access it. In Device Manager, select Driver > Uninstall.