Write a simple Win32 app that:
The HID class driver sends IOCTL_HID_READ_REPORT (IRP_MJ_INTERNAL_DEVICE_CONTROL). The minidriver forwards the request to the lower driver (HIDI2C.sys), then modifies the output buffer.
if (NT_SUCCESS(Params->IoStatus.Status)) PHID_XFER_PACKET transfer = NULL; WdfRequestRetrieveOutputMemory(Request, &memory); transfer = (PHID_XFER_PACKET)WdfMemoryGetBuffer(memory, NULL); // Parse HID report (assume touch digitizer usage page) BYTE* reportData = (BYTE*)(transfer + 1); ULONG reportLen = transfer->OutputBufferLen;
The handler validates input, updates driver’s calibration structure, saves to registry, and optionally applies it to the hardware.
Now, go forth and calibrate – down to the last raw I2C byte.
Calibration is the most critical phase in deploying an I2C-connected touch device under Windows. Without precise calibration, Touch I2C devices suffer from coordinate drifting, missed gestures, and misaligned touch targets.
In EvtDriverDeviceAdd :
Comprehensive Guide to KMDF HID Minidriver for Touch I2C Device Calibration
X_cal = A * X_raw + B * Y_raw + C Y_cal = D * X_raw + E * Y_raw + F
: Your driver. It binds to the I2C transport, fetches raw coordinate data, applies calibration matrices, and structures the data into HID-compliant reports.
// Translate: X' = a*X + b*Y + cx calibrated->X = (LONG)(cal->A * raw->X + cal->B * raw->Y + cal->Cx); calibrated->Y = (LONG)(cal->D * raw->X + cal->E * raw->Y + cal->Cy); // Clamp to touch resolution
| Problem | Symptom | KMDF Debugging Technique | |---------|---------|--------------------------| | I2C clock stretching | Timeout reading registers | Use WPP tracing; check STATUS_IO_TIMEOUT | | Interrupt storms | High CPU, missed touches | Verify edge vs. level trigger in ACPI | | Non-monotonic raw values | Jumps in X/Y | Check I2C buffering; add median filter in DPC | | Registry corruption | Coefficients lost after reboot | Validate WdfRegistryAssignMemory return |