Chris Cant - Writing Windows WDM Device Drivers

Do Isochronous Transfer

Function codes URB_FUNCTION_ISOCH_TRANSFER

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URB Structure _URB_ISOCH_TRANSFER

Use this function to request an isochronous transfer. The TransferBuffer fields specify the data. The data block is split into one or more packets. The number of packets is given in NumberOfPackets. IsoPacket is an array of USBD_ISO_PACKET_DESCRIPTOR structures. Each of these specifies where a packet is in the transfer buffer (i.e., the Offset into the buffer, the Length, and the Status on return of the packet).

GET_ISO_URB_SIZE returns the number of bytes required to hold an isochronous request of the given number of packets.

If the START_ISO_TRANSFER_ASAP bit is set in TransferFlags field, the transfer is started as soon as possible. Otherwise, specify the 32-bit ULONG StartFrame number on which you want the transfer to start, within 1,000 frames of the current frame. The USBD_TRANSFER_ DIRECTION_IN flag bit specifies the direction of data transfer.

Cancel

Function codes URB_FUNCTION_ABORT_PIPE

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URB Structure _URB_PIPE_REQUEST

This function cancels all requests on the pipe with the given PipeHandle.

Set/Clear Feature

Function codes URB_FUNCTION_SET_FEATURE_TO_DEVICE URB_FUNCTION_SET_FEATURE_TO_INTERFACE URB_FUNCTION_SET_FEATURE_TO_ENDPOINT URB_FUNCTION_SET_FEATURE_TO_OTHER URB_FUNCTION_CLEAR_FEATURE_TO_DEVICEURB_FUNCTION_CLEAR_FEATURE_TO_INTERFACE URB_FUNCTION_CLEAR_FEATURE_TO_ENDPOINT URB_FUNCTION_CLEAR_FEATURE_TO_OTHER

Build routine UsbBuildFeatureRequest

URB Structure _URB_CONTROL_FEATURE_REQUEST

This function sets or clears a feature, in a control transfer over the default pipe. Specify a feature code.

Vendor/Class

Function codes URB_FUNCTION_VENDOR_DEVICE URB_FUNCTION_VENDOR_INTERFACE URB_FUNCTION_VENDOR_ENDPOINT URB_FUNCTION_VENDOR_OTHER URB_FUNCTION_CLASS_DEVICE URB_FUNCTION_CLASS_INTERFACE URB_FUNCTION_CLASS_ENDPOINT URB_FUNCTION_CLASS_OTHER

Build routine UsbBuildVendorRequest

URB Structure _URB_CONTROL_VENDOR_OR_CLASS_REQUEST

Use this function to issue a vendor or class-specific command to a device, interface, endpoint, or other device-defined target, in a control transfer over the default pipe.

The TransferBuffer fields specify the data. The USBD_TRANSFER_DIRECTION_IN bit in the TransferFlags field specifies the direction in which the data flows. Specify the USBD_SHORT_ TRANSFER_OK flag bit if a short input transfer is acceptable.

The ReservedBits field is usually zero, but if it is a value between 4 and 31 this value is used for bits 4 to 0 in the SETUP packet bmRequestType field (see Table 20.3 in the last chapter).

The Request, Value, Index, and TransferBuffer fields are set appropriately for the vendor– or class-defined request.

Request Control of Frame Length

Function codes URB_FUNCTION_TAKE_FRAME_LENGTH_CONTROL URB_FUNCTION_RELEASE_FRAME_LENGTH_CONTROL

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URB Structure _URB_FRAME_LENGTH_CONTROL

Use this function to request control of the frame length (i.e., SOF mastership).

Only one client can have control of frame length at any time.

Get Current Frame Length

Function codes URB_FUNCTION_GET_FRAME_LENGTH

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URB Structure _URB_GET_FRAME_LENGTH

Use this function to get the current frame length in the FrameLength field. It also indicates in FrameNumber the first frame in which the frame length can be changed.

Set Current Frame Length

Function codes URB_FUNCTION_SET_FRAME_LENGTH

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URB Structure _URB_SET_FRAME_LENGTH

Use this function to specify the amount to change the current frame length (i.e., 1 or –1 in the FrameLengthDelta field).

You must have control of frame length to issue this URB.

Get Current Frame Number

Function codes URB_FUNCTION_GET_CURRENT_FRAME_NUMBER

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URB Structure _URB_GET_CURRENT_FRAME_NUMBER

Use this function to get the current frame number in FrameNumber.

Gets Beginning Frame of Pattern Transfer

Function codes URB_FUNCTION_SYNC_FRAME

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URB Structure _URB_CONTROL_SYNC_FRAME_REQUEST

This function retrieves the beginning frame of a pattern transfer from an isochronous pipe.

This function is documented, but both the function code and the URB structure are not defined in the W98 and W2000 DDK USB headers.

The chapter has looked in detail at the Windows USB Device Interface (USBDI) and shown how to use it to talk to a USB HID keyboard. The USB class drivers make several Internal IOCTLs available to USB client device drivers. The most important of these lets you issue USB Request Blocks (URBs). Use URBs to do most interactions with your USB device.

The next chapter looks at the core theory of Human Input Devices (HID). The following chapter shows how to use a HID device in a client device driver and Win32 application.

This chapter describes the Human Input Device (HID) model, a standard way of interacting with user input devices. A HID device uses various descriptors to define its capabilities. A Report descriptor details the input reports that it can generate and the output reports it can receive. The next chapter describes how to write Windows client device drivers and user mode applications that can talk to HID devices.

The HID specification is an abstract model for most types of input device that people will use to control their computers. An input device can be a plain old keyboard, for example, a vehicle simulation rudder, or the soft on/off button for the computer.

The HID specification was written originally for USB devices and closely follows the USB descriptor model. However, it is sufficiently generic for HID to be used with other types of device.

Naturally, most of the time a HID device provides input data to the computer. However, you can output to a HID device (e.g., to turn on the NumLock LED on a keyboard). You can also control a feature of the device, such as the font used on a display device or an LED color.

In Windows, the system HID class driver provides an abstract view of the input device. The HID device itself can be a USB device, a IEEE 1394 device or even a plain PC-compatible device, provided an appropriate HID minidriver is written to interface to the bus or device.