From: Jan "Yenya" Kasprzak <kas@fi.muni.cz>
Date: Mon, 3 Feb 2014 17:26:15 +0000 (+0100)
Subject: firmware: faster T/C1 clock
X-Git-Url: https://www.fi.muni.cz/~kas/git//home/kas/public_html/git/?p=heater.git;a=commitdiff_plain;h=164f72d29f27faca0a4b2683f73e96a53edeedee

firmware: faster T/C1 clock

We should have T/C1 as fast as possible (but slow enough to allow for
ADC measurements both in on and off states). Faster T/C1 allows lower
voltage ripple of Vcc, and less LED flicker.
---

diff --git a/firmware/main.c b/firmware/main.c
index 4ac8171..ec58232 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -84,6 +84,7 @@ static unsigned char batt_levels[] = {
 /* output power and PWM calculation */
 #define PWM_TOP	255
 #define PWM_MAX	(PWM_TOP - 8)	// to allow for ADC "batt_off" measurements
+#define PWM_MIN	8		// to allow for ADC "batt_on" measurements
 
 /*
  * The values in power_levels[] array are voltages at which the load
@@ -182,7 +183,15 @@ static void pwm_init()
 	PORTB &= ~_BV(PB4);
 
 	// TCCR1 = _BV(CS10); // clk/1 = 1 MHz
-	TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
+	// TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
+	/*
+	 * clk/64 = 16 kHz. We use PWM_MIN and PWM_MAX, so we have at least
+	 * 8 full T/C1 cycles to do two ADC measurements. The ADC with 125 kHz
+	 * clock can do about 7000-9000 measurement per second, so we should
+	 * be safe both on low and high OCR1B values with this clock
+	 */
+	TCCR1 = _BV(CS12) | _BV(CS11) | _BV(CS10);
+
 	GTCCR = _BV(COM1B1) | _BV(PWM1B);
 	OCR1C = PWM_TOP;
 	// OCR1B = steps[0];
@@ -200,14 +209,14 @@ static void pwm_susp()
 
 ISR(TIM1_OVF_vect)
 {
-	adc_drop = 2;
+	adc_drop = 1;
 	adc_type = 1;
 	adc_start_measurement();
 }
 
 ISR(TIM1_COMPB_vect)
 {
-	adc_drop = 2;
+	adc_drop = 1;
 	adc_type = 0;
 	adc_start_measurement();
 }
@@ -495,6 +504,9 @@ static void calculate_power_level()
 	if (pwm > PWM_MAX)
 		pwm = PWM_MAX;
 
+	if (pwm < PWM_MIN)
+		pwm = PWM_MIN;
+
 	log_byte(0x10 + power_level);
 	log_byte(batt_on8);
 	log_byte(pwm & 0xFF);