From d92ecc1a02b2e054debc1bb9f1732181b7756f63 Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Thu, 28 Mar 2013 23:33:25 +0100
Subject: [PATCH] slow ADC inputs

The fastest-repeated measurements are needed for PWM LEDs. OTOH,
things like buttons, battery voltage, ambient lights, etc. can be
read less frequently, and should be read in a deterministic time frame.
So we will measure PWMLED current in the free-running mode (as fast
as possible), and the other "slow" ADC inputs with each PATTERN_DIV-th
timer tick.
---
 firmware/adc.c    | 39 +++++++++++++++++++++++++++------------
 firmware/lights.h |  2 +-
 firmware/tmr.c    |  3 +--
 3 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/firmware/adc.c b/firmware/adc.c
index 70c2aa1..ef71477 100644
--- a/firmware/adc.c
+++ b/firmware/adc.c
@@ -25,7 +25,7 @@ struct {
 	{ 0, 1, 0 },			// buttons
 };
 
-volatile static unsigned char current_adc;
+volatile static unsigned char current_adc, current_slow_adc;
 static uint16_t adc_sum, zero_count, drop_count, read_count, n_reads_log;
 #define ADC1_GAIN20_OFFSET_SHIFT	6
 static uint16_t adc1_gain20_offset;
@@ -65,14 +65,26 @@ static void setup_mux(unsigned char n)
 
 static void start_next_adc()
 {
-	if (current_adc > 0) {
-		current_adc--;
+	if (current_adc == 0) {
+		if (current_slow_adc > N_PWMLEDS) {
+			// read one of the non-PWMLED ADCs
+			current_adc = --current_slow_adc;
+		} else {
+			// no more non-PWMLEDs to do, start with PWMLEDs
+			current_adc = N_PWMLEDS-1;
+		}
+	} else if (current_adc >= N_PWMLEDS) {
+		// one of the non-PWMLED ADCs just finished, skip to PWMLEDs.
+		current_adc = N_PWMLEDS-1;
 	} else {
-		// TODO: kick the watchdog here.
-		current_adc = NUM_ADCS;
-		return;
+		// next PWMLED
+		current_adc--;
 	}
 
+#if 0
+	log_byte(0x90 + current_adc); // debug ADC switching
+#endif
+
 	adc_sum = 0;
 	// we use the last iteration of zero_count to set up the MUX
 	// to its final destination, hence the "1 +" below:
@@ -98,12 +110,14 @@ static void start_next_adc()
 	ADCSRA |= _BV(ADSC);
 }
 
-void timer_start_adcs()
+void timer_start_slow_adcs()
 {
-	if (current_adc == NUM_ADCS) // Don't start if in progress
-		start_next_adc();
-	else
-		log_byte(0x99); // overrun
+	if (current_slow_adc > N_PWMLEDS) { // Don't start if in progress
+		log_byte(0x80 + current_slow_adc);
+	} else {
+		current_slow_adc = NUM_ADCS;
+		// TODO: kick the watchdog here
+	}
 }
 
 /*
@@ -129,7 +143,8 @@ static uint16_t read_adc_sync()
 void init_adc()
 {
 	unsigned char i;
-	current_adc = NUM_ADCS;
+	current_slow_adc = NUM_ADCS;
+	current_adc = 0;
 
 	ADCSRA = _BV(ADEN)			// enable
 		| _BV(ADPS1) | _BV(ADPS0)	// CLK/8 = 125 kHz
diff --git a/firmware/lights.h b/firmware/lights.h
index e9d48aa..af5eab6 100644
--- a/firmware/lights.h
+++ b/firmware/lights.h
@@ -28,7 +28,7 @@ void inline log_word(uint16_t word) { }
 #define PWMLED_ADC_SHIFT 3 /* 1<<3 measurements per single callback */
 void init_adc();
 void susp_adc();
-void timer_start_adcs();
+void timer_start_slow_adcs();
 
 /* pwm.c */
 /*
diff --git a/firmware/tmr.c b/firmware/tmr.c
index 37b240b..23b70b6 100644
--- a/firmware/tmr.c
+++ b/firmware/tmr.c
@@ -34,9 +34,8 @@ ISR(TIMER0_COMPA_vect)
 	if (--pattern_div == 0) {
 		timer_check_buttons();
 		patterns_next_tick();
+		timer_start_slow_adcs();
 		pattern_div = PATTERN_DIV;
 	}
-
-	timer_start_adcs();
 }
 
-- 
2.39.3