Now, go forth and calibrate – down to the last raw I2C byte. References: Microsoft WDK Documentation, HID v1.11 Specification, I2C HID Guide, KMDF Tutorials.
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TouchCalibMini\Parameters] "CalibMatrix"=hex:01,00,00,00,... A simple linear calibration: kmdf hid minidriver for touch i2c device calibration
This article provides a technical deep dive into architecting a KMDF HID Minidriver that performs on-the-fly calibration for an I2C-connected touch device. We will cover the theory of touch panel calibration, the KMDF/HID minidriver model, I2C transaction handling, and critical code patterns for dynamic parameter adjustment. Unlike USB or Bluetooth HID devices, I2C touch controllers often lack sophisticated onboard processing. Many commodity touch controllers (e.g., from Goodix, FocalTech, or Cypress) provide raw ADC values from a resistive or capacitive matrix. These raw values require transformation into screen coordinates via a calibration formula: Now, go forth and calibrate – down to
While many user-mode calibration tools exist, they suffer from latency, privilege constraints, and non-deterministic behavior. Enter the . By implementing a minidriver at the kernel level, you gain direct control over the I2C transport, real-time calibration parameter injection, and seamless integration with Windows’ Human Interface Device (HID) stack. A simple linear calibration: This article provides a
NTSTATUS TouchCalibEvtIoDeviceControl(WDFQUEUE Queue, WDFREQUEST Request, ...) { switch (ControlCode) { case IOCTL_SET_TOUCH_CALIBRATION: // Read calibration matrix from user buffer WdfRequestRetrieveInputBuffer(Request, sizeof(CALIB_PARAMS), ¶ms, &length); // Store in device context safely WdfDeviceGetDeviceContext(Device)->CalibParams = updatedParams; break; } } The user-mode calibration tool can then call DeviceIoControl to update coefficients without a driver reload. For a multi-touch device, your HID Report Descriptor must conform to the Windows Precision Touchpad (PTP) or HID-over-I2C v1.0 spec. A minimal single-touch descriptor: