// Clamp to HID Logical range (e.g., 0..32767) calibratedX = max(0, min(32767, calibratedX)); calibratedY = max(0, min(32767, calibratedY));
Last insight: Always provide a user-mode calibration tool that sends new matrix values to the driver via DeviceIoControl . The driver stores them in registry, applies them live, and persists across reboots. That dual-layer (kernel enforcement + user control) is what separates production-grade solutions from prototypes.
// Write back *(PUSHORT)(Packet->Buffer + X_OFFSET) = (USHORT)calibratedX; *(PUSHORT)(Packet->Buffer + Y_OFFSET) = (USHORT)calibratedY; Kmdf Hid Minidriver For Touch I2c Device Calibration
[ User Mode ] Touch API (WM_POINTER) ↑ [ Kernel Mode ] HID Class Driver (hidclass.sys) ↑ HID Transport Minidriver (Your Driver) ↑ KMDF I2C Lower Filter / HIDI2C Shim ↑ I2C Controller Driver (SpbCx) Your minidriver must implement the HID_DEVICE_EXTENSION structure and callback functions defined in hidport.h . However, for I2C calibration, we typically implement a (using HID_TRANSPORT_MINIDRIVER_REGISTRATION ) that attaches to the existing HID-I2C transport. 3. The Calibration Model: Linear Transformation Touchscreen calibration is a projective transformation. For most industrial I2C devices, we assume a simple linear mapping:
#define GT911_X_RESOLUTION 0x8140 // Register for max X #define GT911_Y_RESOLUTION 0x8142 // Register for max Y VOID ApplyHardwareCalibration(WDFDEVICE Device) // Clamp to HID Logical range (e
X_screen = A * X_touch + B * Y_touch + C Y_screen = D * X_touch + E * Y_touch + F Where (X_touch, Y_touch) are raw ADC/register values from the I2C device, and (X_screen, Y_screen) are the final HID coordinates reported to the OS.
// Get raw X,Y from Packet->Buffer USHORT rawX = *(PUSHORT)(Packet->Buffer + X_OFFSET); USHORT rawY = *(PUSHORT)(Packet->Buffer + Y_OFFSET); // Apply calibration LONG calibratedX = (LONG)(rawX * CalibA + rawY * CalibB + CalibC); LONG calibratedY = (LONG)(rawX * CalibD + rawY * CalibE + CalibF); // Forward return HidTransportReadReport(DeviceObject
// Write screen resolution to controller's internal mapping I2C_Write(Device, GT911_X_RESOLUTION, SCREEN_WIDTH); I2C_Write(Device, GT911_Y_RESOLUTION, SCREEN_HEIGHT); // Now the controller itself produces transformed coordinates
While user-space calibration tools exist, they fail before the logon screen or during OS recovery environments. The industry solution is a that intercepts, transforms, and corrects touch coordinates at the HID report level. 2. Architecture of a KMDF HID Minidriver A HID minidriver is not a full HID class driver; it is a lightweight adapter that sits between the HID class driver ( HIDCLASS.SYS ) and the I2C controller driver ( HIX2C.SYS or SPB ).
// Forward return HidTransportReadReport(DeviceObject, Packet); Some I2C touch controllers accept calibration commands via HID Feature reports. Your minidriver can intercept USAGE_CALIBRATION writes, re-map them to the I2C device's register set, or override them entirely. 5. Registry-Based vs. ACPI-Based Calibration KMDF drivers cannot easily read large configuration from the registry during a boot-start scenario. The standard approaches: