From 5c6497fb82a5a45cb8f4ecabc094081e259ae6d6 Mon Sep 17 00:00:00 2001
From: Thomas Kolb <thomas@tkolb.de>
Date: Sat, 15 Oct 2022 21:44:27 +0200
Subject: [PATCH] charge_control: block charging if external temperature is too
 low

---
 src/charge_control.c | 49 ++++++++++++++++++++++++++++++++++++--------
 src/charge_control.h |  9 ++++++--
 2 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/src/charge_control.c b/src/charge_control.c
index 3b8a13a..e1898e8 100644
--- a/src/charge_control.c
+++ b/src/charge_control.c
@@ -2,6 +2,7 @@
 
 #include <fxp.h>
 
+#include "bmp280.h"
 #include "power_switch.h"
 #include "measurement.h"
 #include "charge_pump.h"
@@ -10,17 +11,18 @@
 
 #include "charge_control.h"
 
-static const char *CHARGE_STATE_TEXT[] = {
+static const char *CHARGE_STATE_TEXT[CHARGE_NUM_STATES] = {
 	"WAIT_CHARGEPUMP",
 	"INITIAL",
 	"INITIAL_HOLD",
 	"TRANSITION",
 	"FLOAT",
 	"SLEEP",
-	"HIGH_TEMPERATURE"
+	"HIGH_INTERNAL_TEMPERATURE",
+	"LOW_EXTERNAL_TEMPERATURE"
 };
 
-static const char *DISCHARGE_STATE_TEXT[] = {
+static const char *DISCHARGE_STATE_TEXT[DISCHARGE_NUM_STATES] = {
 	"WAIT_CHARGEPUMP",
 	"OK",
 	"VOLTAGE_LOW",
@@ -56,6 +58,9 @@ static fxp_t load_current_limit;
 static fxp_t internal_temperature_limit;
 static fxp_t internal_temperature_recovery;
 
+static fxp_t external_temperature_limit;
+static fxp_t external_temperature_recovery;
+
 static fxp_t sleep_solar_current;
 static fxp_t sleep_solar_excess_voltage;
 
@@ -86,9 +91,15 @@ static enum ChargeState control_solar_charging(
 		solar_switch_onoff_duration = 0;
 	}
 
-	// temperature limit
+	// internal temperature limit: prevent overheating of the power transistors.
 	if(meas->avg_temperature > internal_temperature_limit) {
-		return CHARGE_HIGH_TEMPERATURE;
+		return CHARGE_HIGH_INTERNAL_TEMPERATURE;
+	}
+
+	// external temperature limit: prevent charging the battery if temperature is too low.
+	if(bmp280_are_measurements_valid() &&
+			bmp280_get_temperature() < external_temperature_limit) {
+		return CHARGE_LOW_EXTERNAL_TEMPERATURE;
 	}
 
 	// low-current limit (go to sleep at night)
@@ -195,7 +206,7 @@ static void solar_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 
 			// temperature limit
 			if(meas->temperature > internal_temperature_limit) {
-				charge_state = CHARGE_HIGH_TEMPERATURE;
+				charge_state = CHARGE_HIGH_INTERNAL_TEMPERATURE;
 				break;
 			}
 			break;
@@ -217,7 +228,7 @@ static void solar_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 			break;
 
 
-		case CHARGE_HIGH_TEMPERATURE:
+		case CHARGE_HIGH_INTERNAL_TEMPERATURE:
 			if(charge_state_entered) {
 				power_switch_solar_off();
 			}
@@ -228,6 +239,21 @@ static void solar_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 			}
 			break;
 
+
+		case CHARGE_LOW_EXTERNAL_TEMPERATURE:
+			if(charge_state_entered) {
+				power_switch_solar_off();
+			}
+
+			// this state can only be entered if the BMP280 measurement is valid, so
+			// no need to check it again here.
+			if(bmp280_get_temperature() > external_temperature_recovery) {
+				charge_state = CHARGE_WAIT_CHARGEPUMP;
+				break;
+			}
+			break;
+
+
 		default:
 			// unknown state
 			break;
@@ -329,6 +355,9 @@ void charge_control_init(void)
 	internal_temperature_limit = fxp_div(FXP_FROM_INT(FLASH_CONFIG_INTERNAL_TEMPERATURE_LIMIT), FXP_FROM_INT(10));
 	internal_temperature_recovery = fxp_div(FXP_FROM_INT(FLASH_CONFIG_INTERNAL_TEMPERATURE_RECOVERY), FXP_FROM_INT(10));
 
+	external_temperature_limit = fxp_div(FXP_FROM_INT(FLASH_CONFIG_EXTERNAL_TEMPERATURE_LIMIT), FXP_FROM_INT(10));
+	external_temperature_recovery = fxp_div(FXP_FROM_INT(FLASH_CONFIG_EXTERNAL_TEMPERATURE_RECOVERY), FXP_FROM_INT(10));
+
 	sleep_solar_current = fxp_div(FXP_FROM_INT(FLASH_CONFIG_SLEEP_SOLAR_CURRENT), FXP_FROM_INT(1000));
 	sleep_solar_excess_voltage = fxp_div(FXP_FROM_INT(FLASH_CONFIG_SLEEP_SOLAR_EXCESS_VOLTAGE), FXP_FROM_INT(1000));
 }
@@ -381,7 +410,8 @@ void charge_control_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 bool charge_control_is_idle(void)
 {
 	return (((charge_state == CHARGE_SLEEP)
-					|| (charge_state == CHARGE_HIGH_TEMPERATURE))
+					|| (charge_state == CHARGE_HIGH_INTERNAL_TEMPERATURE)
+					|| (charge_state == CHARGE_LOW_EXTERNAL_TEMPERATURE))
 				&& ((discharge_state == DISCHARGE_VOLTAGE_LOW)
 					|| (discharge_state == DISCHARGE_OVERCURRENT)));
 }
@@ -390,7 +420,8 @@ bool charge_control_is_idle(void)
 bool charge_control_is_charge_blocked(void)
 {
 	switch(charge_state) {
-		case CHARGE_HIGH_TEMPERATURE:
+		case CHARGE_HIGH_INTERNAL_TEMPERATURE:
+		case CHARGE_LOW_EXTERNAL_TEMPERATURE:
 		case CHARGE_WAIT_CHARGEPUMP:
 			return true;
 
diff --git a/src/charge_control.h b/src/charge_control.h
index ecb26bb..003b553 100644
--- a/src/charge_control.h
+++ b/src/charge_control.h
@@ -15,7 +15,10 @@ enum ChargeState
 	CHARGE_TRANSITION,
 	CHARGE_FLOAT,
 	CHARGE_SLEEP,
-	CHARGE_HIGH_TEMPERATURE
+	CHARGE_HIGH_INTERNAL_TEMPERATURE,
+	CHARGE_LOW_EXTERNAL_TEMPERATURE,
+
+	CHARGE_NUM_STATES
 };
 
 enum DischargeState
@@ -23,7 +26,9 @@ enum DischargeState
 	DISCHARGE_WAIT_CHARGEPUMP,
 	DISCHARGE_OK,
 	DISCHARGE_VOLTAGE_LOW,
-	DISCHARGE_OVERCURRENT
+	DISCHARGE_OVERCURRENT,
+
+	DISCHARGE_NUM_STATES
 };
 
 // Error flags