forked from PAWPAW-Mirror/lib_xua
49 lines
2.6 KiB
ReStructuredText
Executable File
49 lines
2.6 KiB
ReStructuredText
Executable File
Audio Controls via Human Interface Device (HID)
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------------------------------------------------
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The design supports simple audio controls such as play/pause, volume up/down etc via the USB Human
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Interface Device Class Specification.
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This functionality is enabled by setting the ``HID_CONTROLS`` define to ``1``. Setting to ``0``
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disables this feature.
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When turned on the following items are enabled:
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#. HID descriptors are enabled in the Configuration Descriptor informing the host that the device has HID interface
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#. A Get Report Descriptor request is enabled in ``endpoint0``.
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#. Endpoint data handling is enabled in the ``buffer`` core
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The Get Descriptor Request enabled in endpoint 0 returns the report descriptor for the HID device.
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This details the format of the HID reports returned from the device to the host. It maps a bit in
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the report to a function such as play/pause.
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The USB Audio Framework implements a report descriptor that should fit most basic audio device controls.
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If further controls are necessary the HID Report Descriptor in ``descriptors.h`` should be modified.
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The default report size is 1 byte with the format as follows:
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.. table:: Default HID Report Format
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+-------------+-------------------------+
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| Bit | Function |
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+=============+=========================+
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| 0 | Play/Pause |
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+-------------+-------------------------+
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| 1 | Scan Next Track |
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+-------------+-------------------------+
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| 2 | Scan Prev Track |
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+-------------+-------------------------+
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| 3 | Volume Up |
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+-------------+-------------------------+
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| 4 | Volume Down |
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+-------------+-------------------------+
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| 5 | Mute |
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+-------------+-------------------------+
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| 6-7 | Unused |
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+-------------+-------------------------+
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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.
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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 function since this could cause issues with servicing other endpoints.
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For a full example please see the HID section in :ref:`usb_audio_sec_l1_audio_sw`.
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