Interrupt aware XPT2046_Touchscreen(uint8_t cs, uint8_t tirq)

On initializing with interrupt pin Poll calls for touch are ignored
unless preceded by falling edge on touch interrupt pin.

User calls are honored until touch detection records a failed pressure
test reading.

This allows the user code to call at a faster rate with no SPI impact so
that the start of a touch is not missed like when polled at a
conservative 100ms.

Included TouchTest sample modified for continuous loop() read to
demonstrate responsiveness and no SPI chatter, versus bright LED when
int pin is not used.

XPT2046_Touchscreen.cpp

@@ -26,23 +26,39 @@
 #define MSEC_THRESHOLD  3
 #define SPI_SETTING     SPISettings(2000000, MSBFIRST, SPI_MODE0)
 
-XPT2046_Touchscreen::XPT2046_Touchscreen(uint8_t cs)
+XPT2046_Touchscreen::XPT2046_Touchscreen(uint8_t cs, uint8_t tirq)
 {
 	csPin = cs;
+	tirqPin = tirq;
 	msraw = 0x80000000;
 	xraw = 0;
 	yraw = 0;
 	zraw = 0;
+	isrWake = true;
 }
 
+static XPT2046_Touchscreen 	*isrPinptr;
+void isrPin(void);
+
 bool XPT2046_Touchscreen::begin()
 {
 	SPI.begin();
 	pinMode(csPin, OUTPUT);
 	digitalWrite(csPin, HIGH);
+	if (255 != tirqPin) {
+		pinMode( tirqPin, INPUT );
+		attachInterrupt( tirqPin, isrPin, FALLING );
+		isrPinptr = this;
+	}
 	return true;
 }
 
+void isrPin( void )
+{
+	XPT2046_Touchscreen *o = isrPinptr;
+	o->isrWake = true;
+}
+
 TS_Point XPT2046_Touchscreen::getPoint()
 {
 	update();
@@ -89,8 +105,10 @@ void XPT2046_Touchscreen::update()
 {
 	int16_t data[6];
 
+	if (!isrWake) return;
 	uint32_t now = millis();
 	if (now - msraw < MSEC_THRESHOLD) return;
+
 	SPI.beginTransaction(SPI_SETTING);
 	digitalWrite(csPin, LOW);
 	SPI.transfer(0xB1 /* Z1 */);
@@ -115,6 +133,7 @@ void XPT2046_Touchscreen::update()
 	if (z < Z_THRESHOLD) { //	if ( !touched ) {
 		// Serial.println();
 		zraw = 0;
+		if (255 != tirqPin) isrWake = false;
 		return;
 	}
 	zraw = z;

XPT2046_Touchscreen.h

@@ -41,17 +41,19 @@ class TS_Point {
 
 class XPT2046_Touchscreen {
 public:
-	XPT2046_Touchscreen(uint8_t cspin);
+	XPT2046_Touchscreen(uint8_t cspin, uint8_t tirq=255);
 	bool begin();
 	TS_Point getPoint();
 	bool touched();
 	void readData(uint16_t *x, uint16_t *y, uint8_t *z);
 	bool bufferEmpty();
 	uint8_t bufferSize() { return 1; }
+// protected:
+	bool isrWake;
 
 private:
 	void update();
-	uint8_t csPin;
+	uint8_t csPin, tirqPin;
 	int16_t xraw, yraw, zraw;
 	uint32_t msraw;
 };

examples/ILI9341Test/ILI9341Test.ino

@@ -9,6 +9,11 @@
 // MOSI=11, MISO=12, SCK=13
 
 XPT2046_Touchscreen ts(CS_PIN);
+#define TIRQ_PIN  2
+//XPT2046_Touchscreen ts(CS_PIN);  // Param 2 - NULL - No interrupts
+//XPT2046_Touchscreen ts(CS_PIN, 255);  // Param 2 - 255 - No interrupts
+//XPT2046_Touchscreen ts(CS_PIN, TIRQ_PIN);  // Param 2 - Touch IRQ Pin - interrupt enabled polling
+
 ILI9341_t3 tft = ILI9341_t3(TFT_CS, TFT_DC);
 
 void setup() {

examples/TouchTest/TouchTest.ino

@@ -4,15 +4,19 @@
 #define CS_PIN  8
 // MOSI=11, MISO=12, SCK=13
 
-XPT2046_Touchscreen ts(CS_PIN);
+//XPT2046_Touchscreen ts(CS_PIN);
+#define TIRQ_PIN  2
+//XPT2046_Touchscreen ts(CS_PIN);  // Param 2 - NULL - No interrupts
+//XPT2046_Touchscreen ts(CS_PIN, 255);  // Param 2 - 255 - No interrupts
+XPT2046_Touchscreen ts(CS_PIN, TIRQ_PIN);  // Param 2 - Touch IRQ Pin - interrupt enabled polling
 
 void setup() {
   Serial.begin(38400);
   ts.begin();
   while (!Serial && (millis() <= 1000));
 }
 
-void loop() {
+void loopB() {
   TS_Point p = ts.getPoint();
   Serial.print("Pressure = ");
   Serial.print(p.z);
@@ -23,5 +27,21 @@ void loop() {
     Serial.print(p.y);
   }
   Serial.println();
-  delay(100);
+  //  delay(100);
+  delay(30);
 }
+
+void loop() {
+  if (ts.touched()) {
+    TS_Point p = ts.getPoint();
+    Serial.print("Pressure = ");
+    Serial.print(p.z);
+    Serial.print(", x = ");
+    Serial.print(p.x);
+    Serial.print(", y = ");
+    Serial.print(p.y);
+    delay(30);
+    Serial.println();
+  }
+}
+