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HID Report Description Size Limit

Jay Jones
Intellectual 330 points

Other Parts Discussed in Thread: CC2540

I am using the CC2540 keyfob and the TI BLE stack to develop a HID Sensor device that will communicate with a Windows 8 platform.  Windows 8 transforms a HID Sensor to a Windows Sensor via the Windows HID Class driver.

The Windows Sensor API provides fixed HID Report data items, namely SENSOR_DATA_TYPE_CUSTOM_VALUE_1 through SENSOR_DATA_TYPE_CUSTOM_VALUE_28.

My problem is that up to and include SENSOR_DATA_TYPE_CUSTOM_VALUE_15, my sensor device communicates with the Windows 8 platform as expected.  Adding ...VALUE_16, generates unpredicatable behavior.  Removing ...VALUE_16, restores back to expected behavior.

I want to send as many data as possible in a single input report for a HID custom sensor.

There appears to be a issue that I suspect may be a size limit.

Is there a size limitation of the HID report descriptor in the TI BLE stack?

  • 0
    TI__Expert 6840 points

    My HID knowledge here is a bit limited. A quick search on hid length (looking for a 1 byte limitation) didn't yield much.

    /* Attribute value lengths */
    #define HID_PROTOCOL_MODE_LEN 1 // HID Protocol Mode
    #define HID_INFORMATION_LEN 4 // HID Information
    #define HID_REPORT_REF_LEN 2 // HID Report Reference Descriptor
    #define HID_EXT_REPORT_REF_LEN 2 // External Report Reference Descriptor

    ctrl-shift-f to find referenced which may help.

    BR,

    -Greg

  • 0 in reply to GregS
    Intellectual 330 points

    Greg,

    Thanks for answering and sorry to take so long to respond.

    My problem is associated with the size of hidReportMap, initialized in hidkbdservice.c.  Beyond a limit (of about 500 bytes if I recall correctly), the connection between the device and my Windows bluetooth 4.0  workstation is not established.  The size of hidReportMap is originally saved in a byte variable but I changed the variable to 16bit integer since the size was >255.