From 5d0f6ceb47eed2282aeb11eb57eebc390add234e Mon Sep 17 00:00:00 2001
From: "Jan \"Yenya\" Kasprzak" <kas@fi.muni.cz>
Date: Thu, 28 Feb 2013 00:56:55 +0100
Subject: [PATCH] battery.c: rework

We can use values in mV instead of 100 mV. We can also provide
the battery level on scale from 1 to 10.
---
 firmware/battery.c | 97 ++++++++++++++++++++++++++++++++++++++++++++--
 firmware/lights.h  |  2 +-
 2 files changed, 94 insertions(+), 5 deletions(-)

diff --git a/firmware/battery.c b/firmware/battery.c
index 01337db..d7123e9 100644
--- a/firmware/battery.c
+++ b/firmware/battery.c
@@ -2,17 +2,30 @@
 
 #include "lights.h"
 
+#define BATTERY_ADC_SHIFT	6
 #define RESISTOR_HI	1500	// kOhm
 #define RESISTOR_LO	 100	// kOhm
 
-volatile unsigned char battery_100mv = 0;
+static volatile uint16_t battery_adcval;
+volatile unsigned char battery_critical;
 
 void init_battery()
 {
-	battery_100mv = 0;
+	battery_adcval = 0;
+	battery_critical = 0;
 }
 
 void battery_adc(uint16_t adcval)
+{
+	if (battery_adcval == 0) {
+		battery_adcval = adcval << BATTERY_ADC_SHIFT;
+	} else { // running average
+		battery_adcval += (adcval
+			- (battery_adcval >> BATTERY_ADC_SHIFT));
+	}
+}
+
+unsigned char battery_100mv()
 {
 	/*
 	 * This is tricky: we need to maintain precision, so we first
@@ -22,9 +35,85 @@ void battery_adc(uint16_t adcval)
 	 * We don't do running average, as the required precision
 	 * is coarse (0.1 V).
 	 */
-	battery_100mv = (unsigned char)
-		((uint16_t)(adcval * (11                   // 1.1V
+	return (unsigned char)
+		((uint16_t)(
+		(battery_adcval >> BATTERY_ADC_SHIFT)
+		* (11                                      // 1.1V
 		* (RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO    // resistor ratio
 		/ 4)) >> 8);                               // divide by 1024
 }
 
+/* convert value in mV to value of ADC shifted by BATTERY_ADC_SHIFT */
+#define MV_TO_ADC(x) \
+	((uint16_t)(((uint32_t)(x) * 1024 * (1 << BATTERY_ADC_SHIFT)) \
+		/ ((uint32_t) 1100 \
+			* ((RESISTOR_HI+RESISTOR_LO)/RESISTOR_LO))))
+
+/* convert value in mV to upper 8 bits of ADC value << BATTERY_ADC_SHIFT */
+#define MV_TO_ADC8(x)	((unsigned char)(MV_TO_ADC(x) >> 8))
+
+/*
+ * Returns number from 1 to 10 (1 = battery almost empty, 10 = full)
+ * Lithium cells have voltage from about 2.9V to 4.1V. We consider battery
+ * above 4V full, and under 3.2V critically low. We guess whether
+ * the battery has two or three cells - voltages above 8.6V are considered
+ * from three-cell battery.
+ */
+unsigned char battery_gauge()
+{
+	unsigned char b8 = battery_adcval >> 8;
+	unsigned char rv;
+
+	if        (b8 < MV_TO_ADC8(2 * 3200)) {
+		rv = 1;
+	} else if (b8 < MV_TO_ADC8(2 * 3475)) {
+		rv = 2;
+	} else if (b8 < MV_TO_ADC8(2 * 3577)) {
+		rv = 3;
+	} else if (b8 < MV_TO_ADC8(2 * 3620)) {
+		rv = 4;
+	} else if (b8 < MV_TO_ADC8(2 * 3741)) {
+		rv = 5;
+	} else if (b8 < MV_TO_ADC8(2 * 3775)) {
+		rv = 6;
+	} else if (b8 < MV_TO_ADC8(2 * 3844)) {
+		rv = 7;
+	} else if (b8 < MV_TO_ADC8(2 * 3930)) {
+		rv = 8;
+	} else if (b8 < MV_TO_ADC8(2 * 4000)) {
+		rv = 9;
+	} else if (b8 < MV_TO_ADC8(2 * 4300)) {
+		rv = 10;
+	} else if (b8 < MV_TO_ADC8(3 * 3200)) { // three-cell battery
+		rv = 1;
+	} else if (b8 < MV_TO_ADC8(3 * 3475)) {
+		rv = 2;
+	} else if (b8 < MV_TO_ADC8(3 * 3577)) {
+		rv = 3;
+	} else if (b8 < MV_TO_ADC8(3 * 3620)) {
+		rv = 4;
+	} else if (b8 < MV_TO_ADC8(3 * 3741)) {
+		rv = 5;
+	} else if (b8 < MV_TO_ADC8(3 * 3775)) {
+		rv = 6;
+	} else if (b8 < MV_TO_ADC8(3 * 3844)) {
+		rv = 7;
+	} else if (b8 < MV_TO_ADC8(3 * 3930)) {
+		rv = 8;
+	} else if (b8 < MV_TO_ADC8(3 * 4000)) {
+		rv = 9;
+	} else {
+		rv = 10;
+	}
+
+	if (rv == 1)
+		battery_critical = 1;
+
+#if 0
+	log_byte(0xbb);
+	log_byte(rv);
+	log_flush();
+#endif
+
+	return rv;
+}
diff --git a/firmware/lights.h b/firmware/lights.h
index 753e281..5032e11 100644
--- a/firmware/lights.h
+++ b/firmware/lights.h
@@ -88,9 +88,9 @@ pattern_t *buttons_setup_status0_pattern_select();
 pattern_t *buttons_setup_status1_pattern_select();
 
 /* battery.c */
-extern volatile unsigned char battery_100mv;
 void battery_adc();
 void init_battery();
+unsigned char battery_gauge();
 
 /* control.c */
 extern pattern_t on1_pattern[];
-- 
2.39.3