This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

change message size for the HID example (TX to host PC)

I'm making an application with an at91SAM7S128 uC and use the USB interface. As starting point I use the demo application. For my application it is required to send two bytes to the PC. I try to change the report, but it when I try the device is not even found by windows.

When I try to double the data I can receive from the PC (as show in the source below) is works fine. Have anyone an idée how I have to modify this report descriptor so I can send two bytes? Or must I change more on the demo program to get it working?

/* HID Report Descriptor */
const BYTE HID_ReportDescriptor[] = {
  HID_UsagePageVendor(0x00),
  HID_Usage(0x01),
  HID_Collection(HID_Application),
    HID_UsagePage(HID_USAGE_PAGE_BUTTON),
    HID_UsageMin(1),
    HID_UsageMax(4),
    HID_LogicalMin(0),
    HID_LogicalMax(1),
    HID_ReportCount(4),
    HID_ReportSize(1),
    HID_Input(HID_Data | HID_Variable | HID_Absolute),
    HID_ReportCount(1),
    HID_ReportSize(4),
    HID_Input(HID_Constant),
    HID_UsagePage(HID_USAGE_PAGE_LED),
    HID_Usage(HID_USAGE_LED_GENERIC_INDICATOR),
    HID_LogicalMin(0),
    HID_LogicalMax(1),
    HID_ReportCount(8),
    HID_ReportSize(2),// <- this work
    HID_Output(HID_Data | HID_Variable | HID_Absolute),
  HID_EndCollection,
};

0 L. v d Heeden over 18 years ago

The problem is solved. I had looked only at the line's I used, but it that's not enough. When You also whant to change the size, keep in mind that the demo source don't send a byte, but only the last 4 bits.

    HID_ReportCount(1),
    HID_ReportSize(4),
    HID_Input(HID_Constant),

This lines gives the problem. (HID_Constant)

If you change the descriptor to this:

const BYTE HID_ReportDescriptor[] = {
  HID_UsagePageVendor(0x00),
  HID_Usage(0x01),
  HID_Collection(HID_Application),
    HID_UsagePage(HID_USAGE_PAGE_BUTTON),
    HID_UsageMin(1),
    HID_UsageMax(254),
    HID_LogicalMin(0),
    HID_LogicalMax(1),
    HID_ReportCount(8),// <- 8 bits
    HID_ReportSize(2),//  <- 2 x TX
    HID_Input(HID_Data | HID_Variable | HID_Absolute),
    HID_UsagePage(HID_USAGE_PAGE_LED),
    HID_Usage(HID_USAGE_LED_GENERIC_INDICATOR),
    HID_LogicalMin(0),
    HID_LogicalMax(1),
    HID_ReportCount(8),
    HID_ReportSize(2),// <- 2 x RX
    HID_Output(HID_Data | HID_Variable | HID_Absolute),
  HID_EndCollection,
};

Sending with more or les data is easier to adjust, and it seems to work fine. For me this is the solution, I hope it will help you when you also have problems.