adding uarte_vs_serial

modules/UARTE_vs_Serial/UARTE_vs_Serial.ino

+// Will Langford
+// Jan 16, 2018
+// Basic example comparing the Adafruit Feather Serial implementation vs Uart
+// the conclusioni is essentially that they're the same (if you're sending a character string anyway)
+// Serial.print is non-blocking (just like the uart_send() function)
+// UNLESS: you're writing data to the UART faster than it can send out... then it will block your code
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdarg.h>
+
+#define n_tx_bytes 20 //only as many as needed
+#define n_rx_bytes 20 //only as many as needed
+const uint8_t pin_rx = 8;
+const uint8_t pin_tx = 6;
+static char uart_tx_data[n_tx_bytes] = {0};
+static char uart_rx_data[n_rx_bytes] = {0};
+
+volatile bool timer2_triggered = false;
+
+const uint8_t enablePin = 27;
+
+uint16_t counter = 0;
+
+extern "C" // for some strange reason this seems necessary for the interrupt to function
+{
+  void TIMER2_IRQHandler(void)
+  {
+      // Clear events
+      NRF_TIMER2->EVENTS_COMPARE[0] = 0;
+
+      timer2_triggered = true;
+  }
+}
+
+void writeToBuffer(char *buff, char *fmt, ...) {
+    va_list args;
+    va_start(args, fmt);
+    vsnprintf(buff, n_tx_bytes, fmt, args);
+    va_end(args);
+}
+
+void uart_setup() {
+  //uart with dma
+  NRF_UARTE0->PSEL.TXD = (pin_tx << UARTE_PSEL_TXD_PIN_Pos) & UARTE_PSEL_TXD_PIN_Msk;
+  NRF_UARTE0->PSEL.RXD = (pin_rx << UARTE_PSEL_RXD_PIN_Pos) & UARTE_PSEL_RXD_PIN_Msk;
+  NRF_UARTE0->CONFIG =  ((UART_CONFIG_PARITY_Excluded << UARTE_CONFIG_PARITY_Pos) & UARTE_CONFIG_PARITY_Msk) 
+                      | ((UARTE_CONFIG_HWFC_Disabled << UARTE_CONFIG_HWFC_Pos) & UARTE_CONFIG_HWFC_Msk);
+  NRF_UARTE0->BAUDRATE = UART_BAUDRATE_BAUDRATE_Baud115200;
+  NRF_UARTE0->ENABLE = (UARTE_ENABLE_ENABLE_Enabled << UARTE_ENABLE_ENABLE_Pos) & UARTE_ENABLE_ENABLE_Msk;
+  
+  NRF_UARTE0->TXD.MAXCNT = n_tx_bytes;
+  NRF_UARTE0->RXD.MAXCNT = n_rx_bytes;
+}
+
+void uart_send() {
+  NRF_UARTE0->EVENTS_ENDTX = 0;
+  NRF_UARTE0->TXD.PTR = (uint32_t)(&uart_tx_data); //reset pointer to start of buffer
+  NRF_UARTE0->TASKS_STARTTX = 1;  //trigger start task to send data to host
+}
+
+void timer2_init()
+{      
+    NVIC_EnableIRQ(TIMER2_IRQn);
+    NVIC_ClearPendingIRQ(TIMER2_IRQn);
+  
+    NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;       // Set the timer in Timer Mode.
+    NRF_TIMER2->PRESCALER = 9;                        
+    NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_16Bit; // 16 bit mode.
+    NRF_TIMER2->TASKS_CLEAR = 1;
+    NRF_TIMER2->CC[0] = 632; // with prescaler 9, this triggers at 200 Hz
+    NRF_TIMER2->EVENTS_COMPARE[0] = 0;
+    NRF_TIMER2->SHORTS = (TIMER_SHORTS_COMPARE0_CLEAR_Enabled << TIMER_SHORTS_COMPARE0_CLEAR_Pos);
+
+    NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos;
+    NVIC_EnableIRQ(TIMER2_IRQn);
+}
+
+void timer2_start() {
+  NRF_TIMER2->TASKS_START = 1;
+}
+
+void setup() {
+//  Serial.begin(115200);
+  
+  NRF_GPIO->DIRSET = (1 << enablePin);
+  NRF_GPIO->OUTSET = (1 << enablePin);
+
+  timer2_init();
+  timer2_start();
+
+  uart_setup();
+}
+
+void loop() { 
+  if (timer2_triggered) {
+
+    // UARTE
+    writeToBuffer(&uart_tx_data[0],"count=%d \n", counter);
+    uart_send();
+
+    // Serial
+//    Serial.print("count=");
+//    Serial.println(counter);
+
+    counter++;
+
+    timer2_triggered = false;
+  }
+}