Added CPPM timer implementation.

include/cppm.h

@@ -0,0 +1,19 @@
+/*
+ * Combined-PPM signal generator
+ */
+
+#ifndef _CPPM_H
+#define _CPPM_H
+
+#include <stdint.h>
+
+#define CPPM_PORT PORTB
+#define CPPM_DDR DDRB
+#define CPPM_PIN PB5
+
+extern volatile uint16_t cppmData[8];
+
+void cppmInit(void);
+
+#endif
+

makefile

@@ -17,6 +17,7 @@ SRC += src/timer.c
 SRC += src/spi.c
 SRC += src/cc2500.c
 SRC += src/rx.c
+SRC += src/cppm.c
 
 OBJ = $(addprefix $(BUILDDIR)/, $(SRC:.c=.o))
 

src/cppm.c

@@ -0,0 +1,123 @@
+/*
+ * Combined-PPM signal generator
+ *
+ * The whole CPPM pulse should be 20ms long.
+ * It contains 8 channels with 2ms each, followed
+ * by 4ms of silence. One channel pulse varies between
+ * 1 and 2 ms. They are seperated with a very short low
+ * pulse of about 0.1ms.
+ *
+ * 20.000us
+ *   - 8 * 2.000us = 16.000us
+ *   - 9 * 100us = 900us
+ *   = 3.100us
+ *
+ *     1     2     3     4     5     6     7     8
+ *    ___   ___   ___   ___   ___   ___   ___   ___   __________
+ * | |   | |   | |   | |   | |   | |   | |   | |   | |          |
+ * | |   | |   | |   | |   | |   | |   | |   | |   | |          |
+ * | |   | |   | |   | |   | |   | |   | |   | |   | |          |
+ * |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|   |_|          |
+ *
+ * States:
+ *  0  1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16    17
+ */
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+#include "cppm.h"
+
+#define MAX_STATES 17
+#define CHANNELS 8
+#define WHOLE_PULSE_WIDTH 20000
+#define PULSE_WIDTH 2000
+#define MAX_PULSE_WIDTH (CHANNELS * PULSE_WIDTH) // 16.000
+#define PULSE_LOW 100
+#define PULSE_LOW_SUM ((CHANNELS + 1) * PULSE_LOW) // 900
+#define MIN_WAIT (WHOLE_PULSE_WIDTH - MAX_PULSE_WIDTH - PULSE_LOW_SUM) // 3100
+#define TIME_AFTER_OVERFLOW 128
+#define TIME_MULTIPLIER 2
+
+volatile uint16_t cppmData[CHANNELS] = { 1500, 1500, 1500, 1500, 1500, 1500, 1500, 1500 };
+volatile uint16_t delaySum = 0;
+volatile uint8_t state = 0;
+volatile uint16_t triggerTimeRemaining = 0;
+
+#define NONE 0
+#define COMPARE_MATCH 1
+#define OVERFLOW 2
+volatile uint8_t triggerState = NONE;
+
+static void triggerIn(uint16_t us);
+static void nextState(void);
+
+void cppmInit(void) {
+    // Set pin to output mode
+    CPPM_DDR |= (1 << CPPM_PIN);
+
+    // Start with a low pulse
+    CPPM_PORT &= ~(1 << CPPM_PIN);
+
+    TCCR0B |= (1 << CS01); // Prescaler: 8
+    TIMSK |= (1 << TOIE0) | (1 << OCIE0A); // Enable Overflow and Compare Match Interrupt
+    OCR0A = 0;
+
+    state = 0;
+    delaySum = MIN_WAIT;
+    triggerIn(PULSE_LOW);
+}
+
+static void triggerIn(uint16_t us) {
+    TCNT0 = 0; // Reset Timer
+    if (us <= (TIME_AFTER_OVERFLOW - 1)) {
+        triggerState = COMPARE_MATCH;
+        OCR0A = us * TIME_MULTIPLIER;
+    } else {
+        triggerState = OVERFLOW;
+        triggerTimeRemaining = us - TIME_AFTER_OVERFLOW;
+    }
+}
+
+static void nextState(void) {
+    state++;
+    if (state > MAX_STATES) {
+        state = 0;
+        delaySum = MIN_WAIT;
+    }
+    if ((state % 2) == 0) {
+        // pulse pause
+        CPPM_PORT &= ~(1 << CPPM_PIN);
+        triggerIn(PULSE_LOW);
+    } else {
+        CPPM_PORT |= (1 << CPPM_PIN);
+        if (state <= 15) {
+            // normal ppm pulse
+            uint8_t index = state / 2;
+            triggerIn(cppmData[index]);
+            delaySum += PULSE_WIDTH - cppmData[index];
+        } else {
+            // sync pulse
+            triggerIn(delaySum);
+        }
+    }
+}
+
+ISR(TIM0_OVF_vect) {
+    if (triggerState == OVERFLOW) {
+        if (triggerTimeRemaining == 0) {
+            triggerState = NONE;
+            nextState();
+        } else {
+            triggerIn(triggerTimeRemaining);
+        }
+    }
+}
+
+ISR(TIM0_COMPA_vect) {
+    if (triggerState == COMPARE_MATCH) {
+        triggerState = NONE;
+        nextState();
+    }
+}
+

src/main.c

@@ -7,6 +7,7 @@
 
 #include "spi.h"
 #include "timer.h"
+#include "cppm.h"
 #include "rx.h"
 
 void watchdogBoot(void) __attribute__((naked)) __attribute__((section(".init3")));
@@ -16,11 +17,13 @@ void watchdogBoot(void) {
 }
 
 void main(void) {
+    cppmInit();
     timerInit();
+
     sei(); // Enable interrupts (required for timer)
-    spiInit();
     wdt_enable(WDTO_120MS); // Trigger Watchdog after 120ms
 
+    spiInit();
     rxInit();
 
     for(;;) { }

src/timer.c

@@ -10,6 +10,7 @@
 volatile time_t systemTime = 0;
 
 void timerInit(void) {
+    // Using 8bit Timer1
     TCCR1 |= (1 << CTC1); // CTC Mode
     TCCR1 |= (1 << CS12) | (1 << CS11) | (1 << CS10); // Prescaler: 64
     OCR1A = 250; // Count to 250