USB HID Reports - different report sizes for different report ID's

[E4dev]

Y'all:

I am writing an application for a ST Cortex M3 processor that uses HID interrupt transfers to send information to the device from Windows. I do not seem to be able to use different sizes for the reports, even though each report has a different reportid. Windows signals an error for every write with a size not equal the size of the largest OUT report in my table. Different sizes in IN and OUT Ep's seem to work. Is that normal behavior or is it related to my report definition (see below).

const uint8_t CustomHID_ReportDescriptor[CUSTOMHID_SIZ_REPORT_DESC] =
  {
    0x06, 0x00, 0xFF,      /* USAGE_PAGE (Vendor Page: 0xFF00) */
    0x09, 0x01,            /* USAGE (Demo Kit)               */
    0x15, 0x00,            /*     LOGICAL_MINIMUM (0)        */
    0x26, 0x7f, 0x00,      /*     LOGICAL_MAXIMUM (1)        */

    /* 12 */
   0xa1, 0x01,      /* Application Collection */
   
    /* Erase */
    0x85, BL_OUT_REPORT_ERASE,        /*     REPORT_ID (2)           */
    0x75, CUSTOMHID_REPORTSIZE_8BIT,  /*     REPORT_SIZE (            */
    0x95, BL_MSG_CNT_ERASE,           /*     REPORT_COUNT (1)           */
    0x09, 0x01,                       /*     USAGE              */
    0x91, 0x82,                       /*     OUTPUT (Data,Var,Abs,Vol)  */

    /* Prog hex record */
    0x85, BL_OUT_REPORT_PROGHEX,        /*     REPORT_ID (3)           */
    0x75, CUSTOMHID_REPORTSIZE_8BIT,            /*     REPORT_SIZE (            */
    0x95, BL_MSG_CNT_PROGHEX,           /*     REPORT_COUNT (1)           */
    0x09, 0x02,                       /*     USAGE                 */
    0x91, 0x82,                       /*     OUTPUT (Data,Var,Abs,Vol)  */


    /* Status */
    0x85, BL_IN_REPORT_STATUS,        /*     REPORT_ID (7)              */
    0x75, CUSTOMHID_REPORTSIZE_8BIT,     /*     REPORT_SIZE (            */
    0x95, BL_MSG_CNT_STATUS,
    0x09, 0x03,                 /*     USAGE            */
    0x81, 0x82,                     /*     INPUT (Data,Var,Abs,Vol)   */
   
    0xc0
  }; /* CustomHID_ReportDescriptor */

Thanks,
HJ

[Jan Axelson]

Make the output buffer big enough to fit the largest report + 1 byte for the report ID. You don't have to use the whole buffer if the report is shorter.

Jan

[E4dev]

Thanks Jan,

I just checked the message with a packet analyzer and Windows indeed only sends a packet with the length of the report size, not the buffer size. Maybe this should be documented in the FAQ, because I could not find it in your book.
-HJ

[Jan Axelson]

Thanks for the suggestion.

Jan