pwm.c: modified for ATtiny45/step-up

So far two PWM channels OC1A/OC1B with sub-LSB resolution possible
(but unused yet) using timer IRQ.

TODO: get rid of OCR1C register and let it count to 255.

projects/step-up/lights.h

@@ -4,7 +4,7 @@
 #define TESTING_FW 1
 
 #define N_LEDS 7
-#define N_PWMLEDS 3
+#define N_PWMLEDS 2
 #define N_PWMLED_MODES 4
 
 #define N_BUTTONS 2
@@ -36,7 +36,7 @@ void timer_start_slow_adcs();
  * A/D converter frequency (125 kHz). Note that this is not the Top
  * value of T/C 1, it is shifted by PWM_STEP_SHIFT as described in pwm.c
  */
-#define PWM_MAX 0x780
+#define PWM_MAX 0x340
 void init_pwm();
 void susp_pwm();
 void pwm_off(unsigned char n);

projects/step-up/pwm.c

@@ -7,7 +7,7 @@
 
 #define PWM_STEP_SHIFT 2 /* sub-LSB precision */
 #define PWM_TOP (((PWM_MAX) + (4 << (PWM_STEP_SHIFT))) >> (PWM_STEP_SHIFT))
-#if PWM_TOP > 0x3FF
+#if PWM_TOP > 0x0FF
 #error PWM_TOP too high
 #endif
 
@@ -37,26 +37,17 @@ void init_pwm()
 
 	enable_pll();
 
-	// PWM channel D is inverted, ...
-	TCCR1C = _BV(COM1D1) | _BV(COM1D0) | _BV(PWM1D);
-	// PWM channels A and B are not
-	TCCR1A = _BV(COM1A1) | _BV(COM1B1) | _BV(PWM1A) | _BV(PWM1B);
-	TCCR1D = 0;
-	TCCR1B = _BV(CS10); 			// no clock prescaling
+	TCCR1 = _BV(CTC1) | _BV(CS10);	// no clock prescaling
+	GTCCR = _BV(COM1A1) | _BV(COM1B1) | _BV(PWM1A) | _BV(PWM1B);
 
-	TC1H = PWM_TOP >> 8;
-	OCR1C = PWM_TOP & 0xFF;				// TOP value
+	OCR1C = PWM_TOP;
+	OCR1A = OCR1B = 0;		// initial stride is 0
 
-	TC1H = PWM_TOP >> 8;		// PWM3 is inverted
-	OCR1D = PWM_TOP & 0xFF;
-
-	TC1H = 0x00;
-	OCR1B = OCR1A = 0;		// initial stride is 0
-
-	DDRB  &= ~(_BV( PB1 ) | _BV( PB3 ) | _BV( PB5 )); // tristate it
-	PORTB &= ~(_BV( PB1 ) | _BV( PB3 ) | _BV( PB5 )); // set to zero
+	DDRB  &= ~(_BV( PB1 ) | _BV( PB4 )); // tristate it
+	PORTB &= ~(_BV( PB1 ) | _BV( PB4 )); // set to zero
 }
 
+#if 0
 void susp_pwm()
 {
 	unsigned char i;
@@ -71,6 +62,7 @@ void susp_pwm()
 
 	PLLCSR &= ~(_BV(PLLE) | _BV(PCKE));
 }
+#endif
 
 void pwm_off(unsigned char n)
 {
@@ -79,35 +71,21 @@ void pwm_off(unsigned char n)
 
 		switch (n) {
 		case 0: DDRB &= ~_BV(PB1); break;
-		case 1: DDRB &= ~_BV(PB3); break;
-		case 2: DDRB &= ~_BV(PB5); break;
+		case 1: DDRB &= ~_BV(PB4); break;
 		}
 	}
 }
 
 static void pwm_update_hw(unsigned char n)
 {
-	unsigned char hi, lo;
 	uint16_t stride = (pwm[n] + step) >> PWM_STEP_SHIFT;
 
-	if (n == 2)
-		stride = PWM_TOP - stride;
-
-	hi = stride >> 8;
-	lo = stride & 0xFF;
-
 	switch (n) {
 	case 0:
-		TC1H = hi;
-		OCR1A = lo;
+		OCR1A = stride;
 		break;
 	case 1:
-		TC1H = hi;
-		OCR1B = lo;
-		break;
-	case 2:
-		TC1H = hi;
-		OCR1D = lo;
+		OCR1B = stride;
 		break;
 	}
 }
@@ -124,8 +102,7 @@ void pwm_set(unsigned char n, uint16_t stride)
 
 		switch(n) {
 		case 0: DDRB |= _BV(PB1); break;
-		case 1: DDRB |= _BV(PB3); break;
-		case 2: DDRB |= _BV(PB5); break;
+		case 1: DDRB |= _BV(PB4); break;
 		}
 	}
 }