Control padding for byte-alignment

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp
Domain
embedded-iot

Research direction

Start by locating the Waratah logic that lays out report fields and automatically inserts padding, then compare it with the keyboard and mouse descriptor examples in this issue. Determine how descriptor authors can request byte alignment or place padding before X and Y, and verify that the resulting report sizes and field offsets match those examples.

Written by the indexing model from the issue text.

Description

The sample for a keyboard (see below) uses 7 bits for each regular button. Thus the array items are not byte-aligned. While it is correct and compact, it's very cumbersome to use, e.g. when programming a MCU as a USB HID device. How can the report size be increased to 8 bits to make life easier?

Similarly for the below mouse descriptor. It's similar to the provided sample, however the buttons are moved to the front of the report. Waratah automatically adds 5 bits of padding, but it's added at the end. Thus, the mouse x and y movements are not byte aligned. How can the padding be moved before x and y?

Keyboard descriptor
[[applicationCollection]]
usage = ['Generic Desktop', 'Keyboard']

    [[applicationCollection.inputReport]]

        # Regular Buttons
        [[applicationCollection.inputReport.arrayItem]]
        usageRange = ['Keyboard/Keypad', 'ErrorRollOver', 'Keyboard Application']
        count = 8

        # Special buttons
        [[applicationCollection.inputReport.variableItem]]
        usageRange = ['Keyboard/Keypad', 'Keyboard LeftControl', 'Keyboard Right GUI']
        logicalValueRange = [0, 1]

    # LEDS
    [[applicationCollection.outputReport]]

        [[applicationCollection.outputReport.variableItem]]
        usageRange = ['LED', 'Num Lock', 'Kana']
        logicalValueRange = [0, 1]
Mouse descriptor
[[applicationCollection]]
usage = ['Generic Desktop', 'Mouse']

    [[applicationCollection.inputReport]]

        [[applicationCollection.inputReport.physicalCollection]]
        usage = ['Generic Desktop', 'Pointer']


            [[applicationCollection.inputReport.physicalCollection.variableItem]]
            usageRange = ['Button', 'Button 1', 'Button 3']
            logicalValueRange = [0, 1]

            [[applicationCollection.inputReport.physicalCollection.variableItem]]
            usage = ['Generic Desktop', 'X']
            sizeInBits = 8
            logicalValueRange = 'maxSignedSizeRange'
            reportFlags = ['relative']

            [[applicationCollection.inputReport.physicalCollection.variableItem]]
            usage = ['Generic Desktop', 'Y']
            sizeInBits = 8
            logicalValueRange = 'maxSignedSizeRange'
            reportFlags = ['relative']
Dominant language
C#
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Forks
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Avg merge
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Merged PRs (30d)
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