X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?p=bike-lights.git;a=blobdiff_plain;f=firmware%2Fpwm.c;h=d68eeb2c3fdf370f69f32a8aa10b1afd68ff48a9;hp=56fb0884e125113a6885a3deb45cba9efe5ad6c8;hb=7f7665a5234d4d5cbd94fed9be55862772f3dc12;hpb=71966b0545b53262ef946c0ae26007664eff32ce

diff --git a/firmware/pwm.c b/firmware/pwm.c
index 56fb088..d68eeb2 100644
--- a/firmware/pwm.c
+++ b/firmware/pwm.c
@@ -5,6 +5,12 @@
 
 #include "lights.h"
 
+#define PWM_STEP_SHIFT 2 /* sub-LSB precision */
+#define PWM_TOP (((PWM_MAX) + (4 << (PWM_STEP_SHIFT))) >> (PWM_STEP_SHIFT))
+#if PWM_TOP > 0x1FF
+#error PWM_TOP too high
+#endif
+
 static uint16_t pwm[N_PWMLEDS];
 static volatile unsigned char step;
 
@@ -38,11 +44,11 @@ void init_pwm()
 	TCCR1D = 0;
 	TCCR1B = _BV(CS10); 			// no clock prescaling
 
-	TC1H = PWM_MAX >> 8;
-	OCR1C = PWM_MAX & 0xFF;				// TOP value
+	TC1H = PWM_TOP >> 8;
+	OCR1C = PWM_TOP & 0xFF;				// TOP value
 
-	TC1H = PWM_MAX >> 8;		// PWM3 is inverted
-	OCR1D = PWM_MAX & 0xFF;
+	TC1H = PWM_TOP >> 8;		// PWM3 is inverted
+	OCR1D = PWM_TOP & 0xFF;
 
 	TC1H = 0x00;
 	OCR1B = OCR1A = 0;		// initial stride is 0
@@ -85,7 +91,7 @@ static void pwm_update_hw(unsigned char n)
 	uint16_t stride = (pwm[n] + step) >> PWM_STEP_SHIFT;
 
 	if (n == 2)
-		stride = PWM_MAX - stride;
+		stride = PWM_TOP - stride;
 
 	hi = stride >> 8;
 	lo = stride & 0xFF;
@@ -108,8 +114,8 @@ static void pwm_update_hw(unsigned char n)
 
 void pwm_set(unsigned char n, uint16_t stride)
 {
-	if (((stride + (1 << PWM_STEP_SHIFT)) >> PWM_STEP_SHIFT) >= PWM_MAX)
-		stride = PWM_MAX << PWM_STEP_SHIFT;
+	if (stride > PWM_MAX)
+		stride = PWM_MAX;
 
 	ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
 		pwm[n] = stride;