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How to code a logical collection with both input and output items? #23
Description
I am rewriting the descriptor for a Braille display with Waratah. As part of my pre-existing descriptor, I have the following:
0x05, 0x41, // Usage Page (Braille Display Page)
0x09, 0x02, // Usage (Braille Row)
0xA1, 0x02, // Collection (Logical)
0x09, 0x05, // Usage (Number of Braille Cells)
0x15, 0x00, // Logical Minimum (0)
0x26, 0xFF, 0x00, // Logical Maximum (255)
0x75, 0x08, // Report Size (8)
0x95, 0x01, // Report Count (1)
0x81, 0x02, // Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0x09, 0x03, // Usage (8 Dot Braille Cell)
0x15, 0x00, // Logical Minimum (0)
0x26, 0xFF, 0x00, // Logical Maximum (255)
0x75, 0x08, // Report Size (8)
0x95, 0x28, // Report Count (40)
0x91, 0x02, // Output (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
0x09, 0xFA, // Usage (Router Set 1)
0xA1, 0x02, // Collection (Logical)
0x0A, 0x00, 0x01, // Usage (Router Button)
0x15, 0x00, // Logical Minimum (0)
0x25, 0x01, // Logical Maximum (1)
0x75, 0x01, // Report Size (1)
0x95, 0x28, // Report Count (40)
0x81, 0x02, // Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
0xC0, // End Collection
In short, I have a logical collection (a Braille row) grouping output items (Braille cells) with input items (routing buttons).
The standard demands that I group the Braille cells and the routing buttons under the same Braille row logical collection.
How do I write this in Waratah?
Activity
matwilli commentedon May 19, 2025
There's no facility in Waratah do to this :(. There was a workaround done for Sensors with a similar back-compat requirement, but this won't work for your scenario.
Choosing to have report 'types' as the top-level construct (and so can't be split amongst CL/CPs) was a deliberate decision to make writing Waratah HID descriptors easier (with the understood cost of significant flexibility).
What platform is this Braille device targeting? If it's targeting Windows there might be another way to compose this descriptor to be compliant.
FelixGruetzmacher commentedon May 26, 2025