Best Practices for KMDF HID Minidriver Touch I2C Device Calibration
It is a best practice to allow calibration updates via the Registry (PnP keys) rather than forcing a firmware flash. You can retrieve OEM-defined calibration data during EvtDevicePrepareHardware .
Log raw I2C values during development to ensure your calibration algorithm maintains at least a 20:1 SNR. kmdf hid minidriver for touch i2c device calibration best
Implement I2CReadRegister() and I2CWriteRegister() using WdfIoTargetSendI2cWriteRead .
| Pitfall | Consequence | Solution | |---------|-------------|----------| | Blocking I2C reads in ISR | High DPC latency | Use WdfRequestSend with no-wait flag | | Incorrect HID descriptor | Touch not recognized | Validate with USB.org HID Descriptor Tool | | Missing synchronization | Corrupt calibration | Guard with WdfSpinLock | | Kernel stack overflow | BSOD | Limit recursion; use WDF_NO_OBJECT_ATTRIBUTES | Best Practices for KMDF HID Minidriver Touch I2C
Perform calibration in EvtInterruptDpc (DISpatch level), not at high IRQL. Avoid floating-point math; use fixed-point integers for speed.
Use the vendor I2C baseline calibration command during power state transitions ( D0Entry ) to nullify environmental electrical noise. Use the vendor I2C baseline calibration command during
To implement this efficiently, parse the incoming I2C payload into a local structure within your read-completion routine. Apply the matrix calculations using fixed-point math if floating-point operations introduce too much overhead in your kernel thread. Once transformed, repackage the coordinates into the official HID input report format defined by your device's HID report descriptor. Finally, complete the pending HID read IRP (I/O Request Packet) to deliver clean, accurate data to Windows.
0x06, 0x00, 0xFF, // USAGE_PAGE (Vendor Defined) 0x09, 0x01, // USAGE (Calibration Control) 0xA1, 0x01, // COLLECTION (Application) 0x85, 0x02, // REPORT_ID (2) 0x09, 0x02, // USAGE (Trigger Calibration Command) 0x15, 0x00, // LOGICAL_MINIMUM (0) 0x25, 0x01, // LOGICAL_MAXIMUM (1) 0x75, 0x08, // REPORT_SIZE (8) 0x95, 0x01, // REPORT_COUNT (1) 0xB1, 0x02, // FEATURE (Data,Var,Abs) 0xC0 // END_COLLECTION Use code with caution. Processing IOCTL_HID_SET_FEATURE