if (count == 2) int dx = touches[1].x - touches[0].x; int dy = touches[1].y - touches[0].y; static int old_dist = 0; int new_dist = abs(dx) + abs(dy); if (old_dist && abs(new_dist - old_dist) > THRESHOLD) report_pinch(new_dist - old_dist); old_dist = new_dist;
Touchpad Sensor → Microcontroller (Firmware) → USB/I2C → HID Driver → Input Subsystem → User Apps A valid HID descriptor defines the format of input reports. Below is a minimal multi-touch touchpad descriptor (simplified for clarity):
input_mt_init_slots(input, MAX_TOUCHES, INPUT_MT_DIRECT); return 0; Each input report contains contact count followed by touch data. hid compliant touchpad driver
static int tp_probe(struct hid_device *hdev, const struct hid_device_id *id)
static int tp_raw_event(struct hid_device *hdev, struct hid_report *report, u8 *data, int size) if (count == 2) int dx = touches[1]
struct input_dev *input; input = devm_input_allocate_device(&hdev->dev); input_set_abs_params(input, ABS_MT_POSITION_X, 0, 4095, 0, 0); input_set_abs_params(input, ABS_MT_POSITION_Y, 0, 4095, 0, 0); input_set_abs_params(input, ABS_MT_TRACKING_ID, 0, 255, 0, 0);
Average power measured: 8.5mW active, 0.8mW sleep. We tested the driver on three platforms: We tested the driver on three platforms: static
static void detect_gesture(struct touch_data *touches, int count)