Is it possible to include a length parameter for the ReceiveFeatureReport function?

[sd016808]

In our web application, we need to reduce the packet size to increase the update frequency.

When using the Logic Analyzer to observe the packet, I noticed that ReceiveFeatureReport always returns the full length as defined in the descriptor. However, with HIDIOCGFEATURE(len) in Linux or HidD_GetFeature in Windows, only a specific length will be obtained.

How can we do it using WebHID?

[nondebug]

Interesting, I didn't realize you could request a shorter report to improve update frequency. Currently, WebHID uses the size of the report defined in the report descriptor and doesn't provide a way to specify the report size.

We could support this by adding an (optional) options parameter to receiveFeatureReport:

device.receiveFeatureReport(reportId, {overrideReportLength: 8});

I'm not sure what this should do if the requested report length is longer than the length defined in the report descriptor. I think for most devices this will cause a device error, but perhaps there are devices where this is necessary.

[sd016808]

Thanks! I am really looking forward for this feature.

[capvor]

@nondebug @beaufortfrancois @marcoscaceres Really need this feature. I have a device that has multiple Feature Reports with different Report IDs, and each Report ID has a different length. However, I've found that in Chromium, it requests all Report IDs using the longest length.

Here is the HID Report Descriptor for my device:

const uint8_t USBD_VendorDefinedHIDReportDescriptor[] = 
{
  0x06, 0x01, 0xFF,     // Usage Page (Vendor-Defined 2)
  0x09, 0x01,           // Usage (Vendor-Defined 1)
  0xA1, 0x01,           // Collection (Application)
  0x15, 0x00,           //     Logical Minimum (0)
  0x26, 0xFF, 0x00,     //     Logical Maximum (255)

  0x75, 0x08,           //     Report Size (8)
  
  0x85, 0x01,           //     Report ID (1)	 
  0x95, 0x40,           //     Report Count (64)
  0x09, 0x01,           //     Usage (Vendor-Defined 1)
  0x81, 0x02,           //     Input (Data,Var,Abs,NWrp,Lin,Pref,NNul,Bit)

  0x85, 0x02,           //     Report ID (2)	 
  0x95, 0x40,           //     Report Count (64)
  0x09, 0x01,           //     Usage (Vendor-Defined 1)
  0x91, 0x02,           //     Output (Data,Var,Abs,NWrp,Lin,Pref,NNul,NVol,Bit)

  0x85, 0x03,           //     Report ID (3)	 
  0x95, 0x40,           //     Report Count (64)
  0x09, 0x01,           //     Usage (Vendor-Defined 1)
  0xB1, 0x02,           //     Feature (Data,Var,Abs,NWrp,Lin,Pref,NNul,NVol,Bit)

  0x85, 0x05,           //     Report ID (5)	 
  0x95, 0x08,           //     Report Count (8)
  0x09, 0x01,           //     Usage (Vendor-Defined 1)
  0xB1, 0x02,           //     Feature (Data,Var,Abs,NWrp,Lin,Pref,NNul,NVol,Bit)
   
  0x85, 0x07,           //     Report ID (7)	 
  0x95, 0x08,           //     Report Count (8)
  0x09, 0x01,           //     Usage (Vendor-Defined 1)
  0xB1, 0x02,           //     Feature (Data,Var,Abs,NWrp,Lin,Pref,NNul,NVol,Bit)
  
  0xC0,                 // End Collection
};

When using the receiveFeatureReport function in Chorme to request a Feature Report with report id 0x05, it requests 65 bytes instead of 9 bytes !