Added Contact Count to Teensy 4 USB Touchscreen

teensy4/usb_desc.c

         0x95, 0x01,                     //   Report Count (1)
         0x09, 0x56,                     //   Usage (Scan Time)
         0x81, 0x02,                     //   Input (variable,absolute)
+        0x09, 0x54,                     //   USAGE (Contact count)
+        0x25, 0x7f,                     //   LOGICAL_MAXIMUM (127)
+        0x95, 0x01,                     //   REPORT_COUNT (1)
+        0x75, 0x08,                     //   REPORT_SIZE (8)
+        0x81, 0x02,                     //   INPUT (Data,Var,Abs)
         0x05, 0x0D,                     //   Usage Page (Digitizers)
         0x09, 0x55,                     //   Usage (Contact Count Maximum)
         0x25, MULTITOUCH_FINGERS,       //   Logical Maximum (10)

teensy4/usb_desc.h

   #define KEYMEDIA_INTERVAL     4
   #define MULTITOUCH_INTERFACE  3	// Touchscreen
   #define MULTITOUCH_ENDPOINT   5
-  #define MULTITOUCH_SIZE       8
+  #define MULTITOUCH_SIZE       9
   #define MULTITOUCH_FINGERS    10
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
   #define ENDPOINT3_CONFIG      ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
   #define MOUSE_INTERVAL        2
   #define MULTITOUCH_INTERFACE  4	// Touchscreen
   #define MULTITOUCH_ENDPOINT   5
-  #define MULTITOUCH_SIZE       8
+  #define MULTITOUCH_SIZE       9
   #define MULTITOUCH_FINGERS    10
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_INTERRUPT + ENDPOINT_TRANSMIT_INTERRUPT
   #define ENDPOINT3_CONFIG      ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
   #define AUDIO_SYNC_ENDPOINT	14
   #define MULTITOUCH_INTERFACE  12	// Touchscreen
   #define MULTITOUCH_ENDPOINT   15
-  #define MULTITOUCH_SIZE       8
+  #define MULTITOUCH_SIZE       9
   #define MULTITOUCH_FINGERS    10
   #define ENDPOINT1_CONFIG	ENDPOINT_TRANSMIT_ONLY
   #define ENDPOINT2_CONFIG	ENDPOINT_TRANSMIT_AND_RECEIVE

teensy4/usb_touch.c

 //  5: Y msb
 //  6: scan time lsb
 //  7: scan time msb
+//  8: contact count
 
 // Called by the start-of-frame interrupt.
 //
 void usb_touchscreen_update_callback(void)
 {
 	static uint8_t microframe_count=0;
+	uint8_t contact_count = 0;
 
 	if (usb_high_speed) {
 		// if 480 speed, run only every 8th micro-frame
 	if (scan_index == 0) {
 		scan_timestamp = millis() * 10;
 		scan_count = 0;
+		// Get the contact count (usage 0x54)
+		// Only set this value on first contact
+		// Subsequent concurrent contacts should report 0
+		for (uint8_t i = 0; i < MULTITOUCH_FINGERS; i++) {
+			if (contactid[i]) contact_count++;
+		}
 	}
 	while (scan_index < MULTITOUCH_FINGERS) {
 		uint32_t press = pressure[scan_index];
 				id &= 0xFE;
 				contactid[scan_index] = 0;
 			}
-			uint8_t buffer[MULTITOUCH_SIZE]; // MULTITOUCH_SIZE = 8
+			//uint8_t buffer[MULTITOUCH_SIZE]; // MULTITOUCH_SIZE = 8
 			txbuffer[0] = id;
 			txbuffer[1] = press;
 			txbuffer[2] = xpos[scan_index];
 			txbuffer[5] = ypos[scan_index] >> 8;
 			txbuffer[6] = scan_timestamp;
 			txbuffer[7] = scan_timestamp >> 8;
+			txbuffer[8] = contact_count;
 			//delayNanoseconds(30);
 			usb_prepare_transfer(&tx_transfer, txbuffer, MULTITOUCH_SIZE, 0);
 			arm_dcache_flush_delete(txbuffer, TX_BUFSIZE);