linkit: proof of concept for basic fast pwm

polybassa · Sep 10, 2016 · 883b04f · 883b04f
1 parent 4b648db
commit 883b04f
Showing 1 changed file with 97 additions and 15 deletions.
diff --git a/LinkIt7688Duo/SerialToSPIandPWM/SerialToSPIandPWM.ino b/LinkIt7688Duo/SerialToSPIandPWM/SerialToSPIandPWM.ino
@@ -19,31 +19,113 @@
 #include <SPI.h>
 
 #define ARRAY_SIZE(X) (sizeof(X) / sizeof(X[0]))
-static const uint8_t GREEN_PIN = 11;
-static const uint8_t BLUE_PIN = 13;
-static const uint8_t RED_PIN = 12;
+
+static const uint8_t PLLFRQ_96_MHZ_OUTPUT = _BV(PDIV1) | _BV(PDIV3);
+static const uint8_t PLLFRQ_64_MHZ_TIMER4 = _BV(PLLTM1);
+static const uint32_t PLL_FREQ_64MHZ = 64000000UL;
+static const uint16_t TIMER4_RESOLUTION = 1023UL;
+static const uint32_t PWM_FREQ = 100 * 1000UL;
+
 static const size_t NUM_OF_LED = 32;
 
-byte slaveSelectPin = 13;
+static int leds[3 * NUM_OF_LED] {32, 64, 128};
+static uint32_t  g_pwm_period;
+
+static void write10BitReg(volatile uint8_t *reg, uint16_t value)
+{
+  TC4H = (value & 0x03ff) >> 8;
+  *reg = (value & 0x00ff);
+}
 
-int leds[3 * NUM_OF_LED] {};
+static void init_pll()
+{
+  static const uint8_t PLLFRQ_96_MHZ_OUTPUT = _BV(PDIV1) | _BV(PDIV3);
+  static const uint8_t PLLFRQ_64_MHZ_TIMER4 = _BV(PLLTM1);
 
+  /* select frequencies */
+  PLLFRQ = PLLFRQ_96_MHZ_OUTPUT | PLLFRQ_64_MHZ_TIMER4;
 
-void leds_update() {
-  analogWrite(RED_PIN,   leds[0]);
-  analogWrite(GREEN_PIN, leds[1]);
-  analogWrite(BLUE_PIN,  leds[2]);
+  /* enable PLL and wait until unlocked */
+  PLLCSR = _BV(PLLE);
+  while(!(PLLCSR & _BV(PLOCK)));
+}
 
-//  digitalWrite(slaveSelectPin, LOW);
-  for (int i = 0; i < sizeof(leds); ++i) {
-    //SPI.transfer(leds[(curOffset + i) % sizeof(leds)]);
+static void init_timer4_pwm()
+{
+  uint8_t prescaler = 1;
+
+  /* enable output compare on port A, B and D*/
+  TCCR4A = _BV(PWM4A) | _BV(PWM4B);
+  TCCR4C = _BV(PWM4D);
+
+  /* enable enhanced mode with more accuracy in OCR4x registers */
+  TCCR4E = _BV(ENHC4);
+
+  /* enable phase and frequency correct PWM mode */
+  TCCR4D = _BV(WGM40);
+
+  /* calculate prescaling and period */
+  g_pwm_period = PLL_FREQ_64MHZ / 2 / PWM_FREQ;
+  while ((g_pwm_period >= TIMER4_RESOLUTION) && (prescaler < 0x10)) {
+    g_pwm_period >>= 1;
+    ++prescaler;
+  }
+
+  /* configure prescaling for timer4 */
+  TCCR4B = prescaler & 0x0F;
+
+  /* configure TOP for timer4 */
+  write10BitReg(&OCR4C, g_pwm_period);
+}
+
+static void pwm_enable()
+{
+  DDRB |= _BV(PORTB6);
+  DDRC |= _BV(PORTC7);
+  DDRD |= _BV(PORTD7);
+  TCCR4A |= _BV(COM4A1) | _BV(COM4B1);
+  TCCR4C |= _BV(COM4D1);
+}
+
+static void pwm_disable()
+{
+  DDRB &= ~(_BV(PORTB6));
+  DDRC &= ~(_BV(PORTC7));
+  DDRD &= ~(_BV(PORTD7));
+  TCCR4A &= ~(_BV(COM4A1) | _BV(COM4B1));
+  TCCR4C &= ~(_BV(COM4D1));
+}
+
+static void pwm_set_duty(volatile uint8_t *reg, uint16_t duty)
+{
+   uint32_t dutyCycle = g_pwm_period * duty;
+   dutyCycle >>= 9;
+   write10BitReg(reg, dutyCycle);
+}
+
+static void leds_update()
+{
+  static volatile uint8_t *const reg[3] = {
+    &OCR4A,
+    &OCR4B,
+    &OCR4D
+  };
+  static uint32_t last[3] = {0};
+
+  for (size_t i = 0; i < 3; ++i) {
+    if (last[i] != leds[i]) {
+      last[i] = leds[i];
+      pwm_set_duty(reg[i], leds[i] << 2);
+    }
   }
-//  digitalWrite(slaveSelectPin, HIGH);
 }
 
 void setup()
 {
-  //pinMode(slaveSelectPin, OUTPUT);
+  init_pll();
+  init_timer4_pwm();
+  pwm_enable();
+
   SPI.begin();
 
   leds_update();
@@ -71,7 +153,7 @@ void loop()
 
     next = next % ARRAY_SIZE(leds);
     if (!next) {
-      leds_update();
+      //leds_update();
       lastUpdate = millis();
     }
   }