From 64a3d3a699cd60b7a6b4b06c5c38689975a3d460 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Thu, 29 Nov 2012 14:36:45 +0100
Subject: [PATCH] firmware: emulate higher resolution of PWM

Emulate the sub-1 LSB resolution of PWM by updating the PWM values
in the timer interrupt routine
---
 firmware/lights.h |  4 ++++
 firmware/pwm.c    | 44 ++++++++++++++++++++++++++++++++++++++++----
 firmware/tmr.c    |  2 ++
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/firmware/lights.h b/firmware/lights.h
index b159ae8..434f051 100644
--- a/firmware/lights.h
+++ b/firmware/lights.h
@@ -29,11 +29,15 @@ void timer_start_adcs();
 
 /* pwm.c */
 #define PWM_MAX 0x1E4 /* This should be different than ADC frequency 125 kHz */
+#define PWM_STEP_SHIFT 2 /* second parameter of pwm_set is shifted by
+			  * PWM_STEP_SHIFT bits to the right before setting
+			  * into HW */
 
 void init_pwm();
 void susp_pwm();
 void pwm_off(unsigned char n);
 void pwm_set(unsigned char n, uint16_t stride);
+void pwm_timer();
 
 /* tmr.c */
 extern volatile uint16_t jiffies;
diff --git a/firmware/pwm.c b/firmware/pwm.c
index 201770f..da9fe3d 100644
--- a/firmware/pwm.c
+++ b/firmware/pwm.c
@@ -4,8 +4,18 @@
 
 #include "lights.h"
 
+static uint16_t pwm[N_PWMLEDS];
+static volatile unsigned char step;
+
 void init_pwm()
 {
+	int i;
+
+	step = 0;
+
+	for (i = 0; i < N_PWMLEDS; i++)
+		pwm[n] = 0;
+
 	/* Async clock */
 	PLLCSR = _BV(PLLE);
 
@@ -37,6 +47,11 @@ void init_pwm()
 
 void susp_pwm()
 {
+	unsigned char i;
+
+	for (i = 0; i < N_PWMLEDS; i++)
+		pwm[i] = 0;
+
 	DDRB &= ~(_BV( PB1 ) | _BV( PB3 ) | _BV( PB5 ));
 	TCCR1D = TCCR1C = TCCR1B = TCCR1A = 0;
 	TIMSK = 0;
@@ -45,6 +60,8 @@ void susp_pwm()
 
 void pwm_off(unsigned char n)
 {
+	pwm[n] = 0;
+
 	switch (n) {
 	case 0: DDRB &= ~_BV(PB1); break;
 	case 1: DDRB &= ~_BV(PB3); break;
@@ -52,12 +69,10 @@ void pwm_off(unsigned char n)
 	}
 }
 
-void pwm_set(unsigned char n, uint16_t stride)
+static void pwm_update_hw(unsigned char n)
 {
 	unsigned char hi, lo;
-
-	if (stride > PWM_MAX)
-		stride = PWM_MAX;
+	uint16_t stride = (pwm[n] + step) >> PWM_STEP_SHIFT;
 
 	if (n == 2)
 		stride = PWM_MAX - stride;
@@ -84,6 +99,27 @@ void pwm_set(unsigned char n, uint16_t stride)
 	}
 }
 
+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;
+
+	pwm[n] = stride;
+	pwm_update_hw(n);
+}
+
+void pwm_timer()
+{
+	unsigned char i;
+
+	if (++step >= (1 << PWM_STEP_SHIFT))
+		step = 0;
+
+	for (i = 0; i < N_PWMLEDS; i++)
+		if (pwm[n])
+			pwm_update_hw(n);
+}
+
 #if 0
 static void inline pwm_handler()
 {
diff --git a/firmware/tmr.c b/firmware/tmr.c
index 5a94f9a..9a0a38b 100644
--- a/firmware/tmr.c
+++ b/firmware/tmr.c
@@ -29,6 +29,8 @@ ISR(TIMER0_COMPA_vect)
 {
 	++jiffies;
 
+	pwm_timer();
+
 	if (--pattern_div == 0) {
 		timer_check_buttons();
 		patterns_next_tick();
-- 
2.39.3