[libhid-discuss] Trying to repair a program using libhid to configure an Ultimarc Joystick

[Xiaofan Chen]

On Wed, Mar 25, 2015 at 12:12 PM, Andrew Silverman
<andrewsi at microsoft.com> wrote:
> What I don't really understand is the 0x43/0xC3 bytes for requesttype
> and the E9/EA/EB values in request. (Assuming that I am correctly understanding
> those param mappings in the existing calls to usb_control_msg, anyway.)
> I can't seem to find anything in the description of USB control messages that
> makes those values make sense.

The requests from 0x40 to 0x43 (and 0x80 to 0x83) are specifically defined
as "vendor" messages, where the vendor can assign any meaning they want.

So you have to carry out reverse engineering to try to understand.

Ref: USB 2.0 Specification Chapter 9.
http://www.usb.org/developers/docs/usb20_docs/


9.3 USB Device Requests

All USB devices respond to requests from the host on the device’s Default
Control Pipe. These requests are made using control transfers. The request
and the request’s parameters are sent to the device in the Setup packet.
The host is responsible for establishing the values passed in the fields
listed in Table 9-2. EverySetup packet has eight bytes.

Table 9-2. Format of Setup Data

Offset: 0
Field: bmRequestType
Size: 1
Value: Bitmap

Characteristics of request:
D7: Data transfer direction
0 = Host-to-device
1 = Device-to-host
D6...5: Type
0 = Standard
1 = Class
2 = Vendor
3 = Reserved
D4...0: Recipient
0 = Device
1 = Interface
2 = Endpoint
3 = Other
4...31 = Reserved


-- 
Xiaofan