Adding gnss code

Gnss_emulator/Gnss_emulator.ino

@@ -0,0 +1,43 @@
+#include <HardwareSerial.h>
+
+#define RX_PIN 16
+#define TX_PIN 17
+
+const int timeOut = 50; // in ms
+
+HardwareSerial SerialUART(2);
+
+const char gngga[] = "$GNGGA,072446.00,3130.5226316,N,12024.0937010,E,4,27,0.5,31.924,M,0.000,M,2.0,*44";
+const char gngga2[] = "$GNGGA,072446.00,3130.5526316,N,12024.1237010,E,4,27,0.5,41.924,M,0.000,M,2.0,*44";
+
+hw_timer_t *timer = NULL;
+portMUX_TYPE timeMux = portMUX_INITIALIZER_UNLOCKED;
+
+volatile bool sendFlag = false;
+bool even = false;
+
+void IRAM_ATTR onTimer() {
+  portENTER_CRITICAL_ISR(&timeMux);
+  sendFlag = true;
+  portEXIT_CRITICAL_ISR(&timeMux);
+}
+
+void setup() {
+  Serial.begin(9600);
+  SerialUART.begin(115200, SERIAL_8N1, RX_PIN, TX_PIN);
+
+  timer = timerBegin(1000000);
+  timerAttachInterrupt(timer, &onTimer);
+  timerAlarm(timer, timeOut*1000, true, 0);
+}
+
+void loop() {
+  if (sendFlag) {
+    portENTER_CRITICAL(&timeMux);
+    sendFlag = false;
+    portEXIT_CRITICAL(&timeMux);
+    even = !even;
+    const uint8_t* message = even? (const uint8_t*)gngga : (const uint8_t*)gngga2;
+    SerialUART.write(message, 82);
+  }
+}