Rework USB Touchscreen handling of pressure & contact ID

teensy3/usb_desc.c

         0x75, 0x01,                     //     Report Size (1)
         0x95, 0x01,                     //     Report Count (1)
         0x81, 0x02,                     //     Input (variable,absolute)
-        0x09, 0x30,                     //     Usage (Pressure)
+        0x09, 0x51,                     //     Usage (Contact Identifier)
         0x25, 0x7F,                     //     Logical Maximum (127)
         0x75, 0x07,                     //     Report Size (7)
         0x95, 0x01,                     //     Report Count (1)
         0x81, 0x02,                     //     Input (variable,absolute)
-        0x09, 0x51,                     //     Usage (Contact Identifier)
+        0x09, 0x30,                     //     Usage (Pressure)
         0x26, 0xFF, 0x00,               //     Logical Maximum (255)
         0x75, 0x08,                     //     Report Size (8)
         0x95, 0x01,                     //     Report Count (1)
         0x95, 0x01,                     //   Report Count (1)
         0x09, 0x56,                     //   Usage (Scan Time)
         0x81, 0x02,                     //   Input (variable,absolute)
-        //0x09, 0x54,                     //   Usage (Contact Count)
-        //0x25, MULTITOUCH_FINGERS,       //   Logical Maximum (10)
-        //0x75, 0x08,                     //   Report Size (8)
-        //0x95, 0x01,                     //   Report Count (1)
-        //0x81, 0x02,                     //   Input (variable,absolute)
         0x05, 0x0D,                     //   Usage Page (Digitizers)
         0x09, 0x55,                     //   Usage (Contact Count Maximum)
         0x25, MULTITOUCH_FINGERS,       //   Logical Maximum (10)

teensy3/usb_dev.c

 			reply_buffer[0] = MULTITOUCH_FINGERS;
 			data = reply_buffer;
 			datalen = 1;
+		} else if (setup.wValue == 0x0100 && setup.wIndex == MULTITOUCH_INTERFACE) {
+			memset(reply_buffer, 0, 8);
+			data = reply_buffer;
+			datalen = 8;
 		} else {
 			endpoint0_stall();
 			return;

teensy3/usb_touch.c

 /* Teensyduino Core Library
  * http://www.pjrc.com/teensy/
- * Copyright (c) 2017 PJRC.COM, LLC.
+ * Copyright (c) 2018 PJRC.COM, LLC.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
 
 #include "usb_dev.h"
 #include "usb_touch.h"
-#include "core_pins.h" // for yield()
+#include "core_pins.h" // for millis()
 #include "HardwareSerial.h"
-#include <string.h> // for memcpy()
 
 #ifdef MULTITOUCH_INTERFACE // defined by usb_dev.h -> usb_desc.h
 #if F_CPU >= 20000000
 
 static uint8_t  prev_id=0;
-static uint8_t  pressure[MULTITOUCH_FINGERS];
+static uint8_t  scan_index=0;
+static uint8_t  scan_count=0;
 static uint8_t  contactid[MULTITOUCH_FINGERS];
+static uint8_t  pressure[MULTITOUCH_FINGERS];
 static uint16_t xpos[MULTITOUCH_FINGERS];
 static uint16_t ypos[MULTITOUCH_FINGERS];
-
-static uint8_t  scan_state=0;
-static uint8_t  scan_remain=0; // number of finger to left to transmit on this scan
-static uint8_t  scan_index=0;  // index of next (possible) finger to transmit
-static uint8_t  scan_pressure[MULTITOUCH_FINGERS];
 static uint16_t scan_timestamp;
 
 
 void usb_touchscreen_press(uint8_t finger, uint32_t x, uint32_t y, uint32_t press)
 {
-	uint8_t id;
-
 	if (finger >= MULTITOUCH_FINGERS) return;
-	press >>= 1;
-	if (press > 127) press = 127;
+	if (press > 255) press = 255;
 	if (x > 32767) x = 32767;
 	if (y > 32767) y = 32767;
-	if (pressure[finger] == 0) {
-		id = prev_id + 1;
-		if (id == 0) id = 1;
+	__disable_irq();
+	if (pressure[finger] == 0 && press > 0) {
+		// Begin a new finger touch, assign a
+		// new Contact Identifier (usage 0x51)
+		uint8_t id = prev_id + 1;
+		if (id == 0 || id > 127) id = 1;
 		prev_id = id;
-		contactid[finger] = id;
+		contactid[finger] = (id << 1) | 1;
 	}
 	xpos[finger] = x;
 	ypos[finger] = y;
-	pressure[finger] = (press << 1) | 1;
+	pressure[finger] = press;
+	__enable_irq();
 }
 
+// User should allow at least 12 ms after release before starting a
+// new touch with press, in case the host's driver does not properly
+// parse a change in contact identifier to mean a new touch.
+
 void usb_touchscreen_release(uint8_t finger)
 {
 	if (finger >= MULTITOUCH_FINGERS) return;
 }
 
 // touch report
-//  0: on/off + pressure
-//  1: contact id
+//  0: contact id + on/off
+//  1: pressure
 //  2: X lsb
 //  3: X msb
 //  4: Y lsb
 //  5: Y msb
 //  6: scan time lsb
 //  7: scan time msb
-//  (no longer used) 8: contact count
-
-static int usb_touchscreen_transmit(int index, int count)
-{
-	usb_packet_t *tx_packet;
-	tx_packet = usb_malloc();
-	if (tx_packet == NULL) return 0;
-	*(tx_packet->buf + 0) = pressure[index];
-	*(tx_packet->buf + 1) = contactid[index];
-	*(tx_packet->buf + 2) = xpos[index];
-	*(tx_packet->buf + 3) = xpos[index] >> 8;
-	*(tx_packet->buf + 4) = ypos[index];
-	*(tx_packet->buf + 5) = ypos[index] >> 8;
-	*(tx_packet->buf + 6) = scan_timestamp;
-	*(tx_packet->buf + 7) = scan_timestamp >> 8;
-	//*(tx_packet->buf + 8) = count;
-	tx_packet->len = 8;
-	usb_tx(MULTITOUCH_ENDPOINT, tx_packet);
-	return 1;
-}
 
 
 // Called by the start-of-frame interrupt.
 //
 void usb_touchscreen_update_callback(void)
 {
-	int i, r, count=0;
-
-	if (scan_state == 0) {
+	if (scan_index == 0) {
 		if (usb_tx_packet_count(MULTITOUCH_ENDPOINT) > 1) {
 			// wait to begin another scan if if more than
 			// one prior packet remains to transmit
 			return;
 		}
-		// copy the pressure data - whether each finger is
-		// in contact at the moment of this "scan"
-		memcpy(scan_pressure, pressure, MULTITOUCH_FINGERS);
-		for (i=0; i < MULTITOUCH_FINGERS; i++) {
-			if (scan_pressure[i] > 0) count++;
-		}
-		if (count > 0) {
-			scan_remain = count;
-			scan_index = 0;
-			scan_timestamp = millis() * 10;
-		} else {
-			scan_remain = 0;
-		}
+		scan_timestamp = millis() * 10;
+		scan_count = 0;
 	}
-	if (scan_remain > 0) {
-		for (i = scan_index; i < MULTITOUCH_FINGERS; i++) {
-			if (scan_pressure[i] > 0) break;
+	while (scan_index < MULTITOUCH_FINGERS) {
+		uint32_t press = pressure[scan_index];
+		uint32_t id = contactid[scan_index];
+		if (id) {
+			usb_packet_t *tx_packet;
+			tx_packet = usb_malloc();
+			if (tx_packet == NULL) return;
+			if (press == 0) {
+				// End a finger touch.  One final packet sent
+				// with same Contact Identifier (usage 0x51)
+				// and Tip Switch (usage 0x42) = zero
+				id &= 0xFE;
+				contactid[scan_index] = 0;
+			}
+			*(tx_packet->buf + 0) = id;
+			*(tx_packet->buf + 1) = press;
+			*(tx_packet->buf + 2) = xpos[scan_index];
+			*(tx_packet->buf + 3) = xpos[scan_index] >> 8;
+			*(tx_packet->buf + 4) = ypos[scan_index];
+			*(tx_packet->buf + 5) = ypos[scan_index] >> 8;
+			*(tx_packet->buf + 6) = scan_timestamp;
+			*(tx_packet->buf + 7) = scan_timestamp >> 8;
+			tx_packet->len = 8;
+			usb_tx(MULTITOUCH_ENDPOINT, tx_packet);
+			scan_index++;
+			return;
 		}
-		r = usb_touchscreen_transmit(i, (scan_state == 0) ? scan_remain : 0);
-		if (!r) return;
-		scan_index = i + 1;
-		scan_remain--;
+		scan_index++;
 	}
-	if (++scan_state >= MULTITOUCH_ENDPOINT) {
-		scan_state = 0;
+	if (++scan_count >= MULTITOUCH_FINGERS) {
+		// when done early, wait to restart another scan
+		scan_index = 0;
 	}
 }