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This functionality is enabled by setting the

HID_CONTROLS

deﬁne to

. Setting to

disables this feature.

When turned on the following items are enabled:

HID descriptors are enabled in the Conﬁguration Descriptor informing the host

that the device has HID interface

2. A Get Report Descriptor request is enabled in endpoint0.

3. Endpoint data handling is enabled in the buffer core

The Get Descriptor Request enabled in endpoint 0 returns the report descriptor for

the HID device. This details the format of the HID reports returned from the device

to the host. It maps a bit in the report to a function such as play/pause.

The USB Audio Framework implements a report descriptor that should ﬁt most basic

audio device controls. If further controls are neccisary the HID Report Descriptor

descriptors_2.h

should be modiﬁed. The default report size is 1 byte with the

format as follows:

Bit Function

0 Play/Pause

1 Scan Next Track

2 Scan Prev Track

3 Volume Up

4 Volume Down

5 Mute

6-7 Unused

Figure 22:

Default HID

Report

Format

On each HID report request from the host the function

Vendor_ReadHidButtons(unsigned char hidData[])

is called from

buffer()

. This function is passed an array

hidData[]

by reference.

The programmer should report the state of his buttons into this array. For

example, if a volume up command is desired, bit 3 should be set to 1, else 0.

Since the

Vendor_ReadHidButtons()

function is called from the

buffer

logical core,

care should be taken not to add to much execution time to this functon since this

could cause issues with servicing other endpoints.

For a full example please see the HID section in §3.18.

3.16 Apple Authentication (iAP)

The XMOS device is capable of authenticating with Apple devices that support USB

Host Mode using an Apple Coprocessor IC. Information regarding this process is

protected by the Made For iPod (MFI) program and associated licensing. Please

contact XMOS for details.

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