ugly interrupt-based stepper control

firmware/src/constants.h

@@ -30,6 +30,6 @@
 
 // --- Z axis motor
 
-#define STEPPER_ENABLE 10
-#define STEPPER_DIR 8
-#define STEPPER_STEP 9
+#define STEPPER_ENABLE A0
+#define STEPPER_STEP A1
+#define STEPPER_DIR A2

firmware/src/main.cpp

@@ -52,6 +52,10 @@ void loop() {
       sadBuzz();
     } else if (key == KEY_C) {
       beep();
+    } else if (digit == 4) {
+      demo_moveBy(-8000);
+    } else if (digit == 5) {
+      demo_moveBy(8000);
     } else {
       tick();
     }
@@ -65,6 +69,6 @@ void loop() {
   if (auto event = handleEncoder()) {
     tick();
     Serial.println(event == ENCODER_CLOCKWISE ? "Clockwise" : "Counter-clockwise");
-    demoStepper(event == ENCODER_CLOCKWISE ? LOW : HIGH);
+    demo_moveBy(event == ENCODER_CLOCKWISE ? 800 : -800);
   }
 }

firmware/src/stepper.cpp

@@ -1,6 +1,14 @@
 #include <Arduino.h>
 #include "constants.h"
 
+/*
+
+ A4988 Stepper Motor Driver.
+
+ NOTE: minimum pulse width 1us high, 1us low
+
+*/
+
 void setupStepper() {
   pinMode(STEPPER_ENABLE, OUTPUT);
   pinMode(STEPPER_DIR, OUTPUT);

firmware/src/timer.cpp

@@ -1,21 +1,34 @@
 #include <Arduino.h>
+#include "constants.h"
 
-#define DEMO_TRIGGER_MS 1500
+#define DEMO_REPORT_SECONDS 2
+#define DEMO_TRIGGER_MS DEMO_REPORT_SECONDS * 1000
+
+#if F_CPU != 16000000
+  #error "Unsupported F_CPU"
+#endif
 
 void setupTimer() {
-  // Set up Timer 0 to trigger interrupt every 1ms
-  // Timer 0 is already used and configured by Arduino for millis()
-  // however it uses TOIE0 (overflow interrupt), so we'll use OCIE0A:
-  //   When this bit is written to one, and the I-flag in the Status Register is set
-  //   (interrupts globally enabled), the Timer/Counter0 Output Compare A Match interrupt is enabled
-  //   The corresponding Interrupt Vector is executed when the OCF0A Flag, located in TIFR0, is set.
-  OCR0A = 0xAF; // any number is OK, it will trigger at some point during the counter
-  TIMSK0 |= _BV(OCIE0A);
+  noInterrupts();
+  // reset timer settings
+  TCCR1A = 0;
+  TCCR1B = 0;
+  TCNT1 = 0;
+  // 256 prescaler (16MHz / 256 = 62.5kHz)
+  TCCR1B |= (1 << CS12);
+  // CTC mode (Clear Timer on Compare Match)
+  TCCR1B |= (1 << WGM12);
+  // interrupt at 62.5kHz / (OCR1A + 1)
+  OCR1A = 19;
+  // enable timer
+  TIMSK1 |= (1 << OCIE1A);
+  interrupts();
 }
 
 // incremented every DEMO_TRIGGER_MS by interrupt,
 // read and decremented by main loop
 volatile uint8_t timerEvents = 0;
+uint8_t demoCounter = 0;
 
 void demoTimer() {
   bool shouldTrigger = false;
@@ -28,19 +41,34 @@ void demoTimer() {
   interrupts();
 
   if (shouldTrigger) {
-    Serial.println("Timer tick!");
+    demoCounter += DEMO_REPORT_SECONDS;
+    Serial.print("Uptime: ");
+    Serial.print(demoCounter);
+    Serial.println("s");
   }
 }
 
+volatile int16_t stepsLeft = 0;
+
+void demo_moveBy(int16_t steps) {
+  bool dir;
+
+  noInterrupts();
+  stepsLeft += steps;
+  dir = steps > 0 ? LOW : HIGH;
+  digitalWrite(STEPPER_DIR, dir);
+  interrupts();
+}
+
+volatile uint16_t timerTicks = 0;
 volatile uint16_t timerMillis = 0;
 
-// triggers every 1ms
-ISR(TIMER0_COMPA_vect) {
-  timerMillis++;
-  if (timerMillis >= DEMO_TRIGGER_MS) {
-    timerMillis -= DEMO_TRIGGER_MS;
-    timerEvents++;
-  }
+ISR(TIMER1_COMPA_vect) {
+  if (stepsLeft != 0) {
+    stepsLeft += stepsLeft > 0 ? -1 : 1;
 
-  // TODO: Add motor encoder reading, calculate required carriage offset, control stepper
+    // pulse STEP
+    PORTC |= 1<<1;
+    PORTC &= ~(1<<1);
+  }
 }

firmware/src/timer.h

@@ -1,2 +1,4 @@
 void setupTimer();
 void demoTimer();
+
+void demo_moveBy(int16_t steps);