Initialize the addon board

Whenever overload is detected, the time that must pass before the load is
turned on again is doubled. If the load was on for 5 minutes, the retry time is
reset to the configured value.

src/addon_io.c

@@ -0,0 +1,35 @@
+#include <libopencm3/stm32/gpio.h>
+
+#include "pinout.h"
+
+#include "addon_io.h"
+
+static const uint32_t OUTPUT_LIST[2] = {ADDON_ISO_IO_OUT1, ADDON_ISO_IO_OUT2};
+
+void addon_io_init(void)
+{
+	// Isolated outputs configuration: output, initially low = off
+	gpio_clear(ADDON_ISO_IO_PORT, ADDON_ISO_IO_OUT1 | ADDON_ISO_IO_OUT2);
+	gpio_mode_setup(ADDON_ISO_IO_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, ADDON_ISO_IO_OUT1 | ADDON_ISO_IO_OUT2);
+
+	// Isolated inputs configuration: input, no pull resistors
+	gpio_mode_setup(ADDON_ISO_IO_PORT, GPIO_MODE_INPUT, GPIO_PUPD_NONE, ADDON_ISO_IO_IN);
+}
+
+
+void addon_io_iso_out_on(uint8_t idx)
+{
+	gpio_set(ADDON_ISO_IO_PORT, OUTPUT_LIST[idx]);
+}
+
+
+void addon_io_iso_out_off(uint8_t idx)
+{
+	gpio_clear(ADDON_ISO_IO_PORT, OUTPUT_LIST[idx]);
+}
+
+
+bool addon_io_read_iso_in(void)
+{
+	return gpio_get(ADDON_ISO_IO_PORT, ADDON_ISO_IO_IN) != 0;
+}

src/addon_io.h

@@ -0,0 +1,14 @@
+#ifndef ADDON_IO_H
+#define ADDON_IO_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+void addon_io_init(void);
+
+void addon_io_iso_out_on(uint8_t idx);
+void addon_io_iso_out_off(uint8_t idx);
+
+bool addon_io_read_iso_in(void);
+
+#endif // ADDON_IO_H

src/bmp280.c

@@ -0,0 +1,284 @@
+#include <libopencm3/stm32/i2c.h>
+#include <libopencm3/stm32/gpio.h>
+
+#include "i2c_dma.h"
+
+#include "pinout.h"
+
+#include "bmp280_comp.h"
+#include "bmp280.h"
+
+#define BMP280_7BIT_ADDR 0x76
+
+typedef enum {
+	READY,
+	SEND_REQUEST,
+	WAIT_MEASUREMENT_COMPLETE,
+	READ_RESULTS,
+	COMPENSATE_TEMPERATURE,
+	COMPENSATE_PRESSURE,
+	ERROR   // set by the I²C callback in case of errors/timeout
+} bmp280_readout_state_t;
+
+static bmp280_readout_state_t m_readout_state;
+
+// calibration value cache, shared with bmp280_comp.c
+
+extern uint16_t dig_T1;
+extern  int16_t dig_T2;
+extern  int16_t dig_T3;
+
+extern uint16_t dig_P1;
+extern  int16_t dig_P2;
+extern  int16_t dig_P3;
+extern  int16_t dig_P4;
+extern  int16_t dig_P5;
+extern  int16_t dig_P6;
+extern  int16_t dig_P7;
+extern  int16_t dig_P8;
+extern  int16_t dig_P9;
+
+static fxp_t m_last_temperature = 0;
+static fxp_t m_last_pressure = 0;
+static bool m_measurements_valid = false;
+
+static int32_t m_temp_raw;
+static int32_t m_press_raw;
+
+
+static void cb_i2c_dma(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen);
+
+
+bool bmp280_init(void)
+{
+	m_measurements_valid = false;
+
+	// configure pins for I2C1
+	gpio_set_af(BMP280_I2C_PORT, GPIO_AF4, BMP280_I2C_SCL | BMP280_I2C_SDA);
+	gpio_mode_setup(BMP280_I2C_PORT, GPIO_MODE_AF, GPIO_PUPD_PULLUP, BMP280_I2C_SCL | BMP280_I2C_SDA);
+
+	// Set up I²C
+	i2c_reset(I2C1);
+
+	i2c_set_speed(I2C1, i2c_speed_sm_100k, 48);
+
+	i2c_peripheral_enable(I2C1);
+
+	// Set up the Chip
+	uint8_t wdata[2];
+	uint8_t rdata[32];
+	uint8_t wsize, rsize;
+
+	// check for chip presence by accessing the chip id register (not a proper read!)
+	i2c_set_7bit_address(I2C1, BMP280_7BIT_ADDR);
+	i2c_set_write_transfer_dir(I2C1);
+	i2c_set_bytes_to_transfer(I2C1, 1);
+	i2c_enable_autoend(I2C1);
+	i2c_send_start(I2C1);
+
+	uint32_t timeout = 1000000;
+	while(--timeout && !i2c_transmit_int_status(I2C1)); // wait for the address transfer to complete
+
+	i2c_send_data(I2C1, 0xD0);
+
+	if((timeout == 0) || i2c_nack(I2C1)) {
+		// something went wrong during communication
+		goto err_out;
+	}
+
+	// read the chip ID
+	wsize = 0;
+	wdata[wsize++] = 0xD0;
+	rsize = 1;
+
+	i2c_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rdata, rsize);
+
+	if(rdata[0] != 0x58) {
+		// unexpected chip id
+		goto err_out;
+	}
+
+	// read calibration data
+	wsize = 0;
+	wdata[wsize++] = 0x88; // first calibration data register of first block
+	rsize = 0xA1 + 1 - 0x88;
+
+	i2c_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rdata, rsize);
+
+	dig_T1 = (((uint16_t)rdata[ 1]) << 8) | rdata[ 0]; // 0x88, 0x89
+	dig_T2 =  (((int16_t)(int8_t)rdata[ 3]) << 8) | rdata[ 2]; // 0x8A, 0x8B
+	dig_T3 =  (((int16_t)(int8_t)rdata[ 5]) << 8) | rdata[ 4]; // 0x8C, 0x8D
+
+	dig_P1 = (((uint16_t)rdata[ 7]) << 8) | rdata[ 6]; // 0x8E, 0x8F
+	dig_P2 =  (((int16_t)(int8_t)rdata[ 9]) << 8) | rdata[ 8]; // 0x90, 0x91
+	dig_P3 =  (((int16_t)(int8_t)rdata[11]) << 8) | rdata[10]; // 0x92, 0x93
+	dig_P4 =  (((int16_t)(int8_t)rdata[13]) << 8) | rdata[12]; // 0x94, 0x95
+	dig_P5 =  (((int16_t)(int8_t)rdata[15]) << 8) | rdata[14]; // 0x96, 0x97
+	dig_P6 =  (((int16_t)(int8_t)rdata[17]) << 8) | rdata[16]; // 0x98, 0x99
+	dig_P7 =  (((int16_t)(int8_t)rdata[19]) << 8) | rdata[18]; // 0x9A, 0x9B
+	dig_P8 =  (((int16_t)(int8_t)rdata[21]) << 8) | rdata[20]; // 0x9C, 0x9D
+	dig_P9 =  (((int16_t)(int8_t)rdata[23]) << 8) | rdata[22]; // 0x9E, 0x9F
+
+	i2c_dma_init(cb_i2c_dma);
+
+	return true;
+
+err_out:
+	return false;
+}
+
+
+static void trigger_read_status_register(void)
+{
+	uint8_t wdata[1];
+	uint8_t wsize = 0, rsize;
+
+	wdata[wsize++] = 0xF3; // status register
+	rsize = 1;
+
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rsize);
+}
+
+
+static void trigger_read_results(void)
+{
+	uint8_t wdata[1];
+	uint8_t wsize = 0, rsize;
+
+	wdata[wsize++] = 0xF7;
+	rsize = 8;
+
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, rsize);
+}
+
+
+static void cb_i2c_dma(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen)
+{
+	(void)rlen;
+
+	switch(evt) {
+		case I2C_DMA_EVT_TRANSFER_COMPLETE:
+			switch(m_readout_state) {
+				case SEND_REQUEST:
+					m_readout_state = WAIT_MEASUREMENT_COMPLETE;
+					trigger_read_status_register();
+					break;
+
+				case WAIT_MEASUREMENT_COMPLETE:
+					if((rdata[0] & 0x09) != 0) {
+						// either "measuring" or "im_update" is active, so measurement is not complete yet.
+						// try again:
+						trigger_read_status_register();
+					} else {
+						m_readout_state = READ_RESULTS;
+						trigger_read_results();
+					}
+					break;
+
+				case READ_RESULTS:
+					m_press_raw =
+						((int32_t)rdata[0] << 12)         // press_msb (0xF7)
+						| ((int32_t)rdata[1] << 4)        // press_lsb (0xF8)
+						| ((int32_t)rdata[2] >> 4);       // press_xlsb (0xF9)
+
+					m_temp_raw =
+						((int32_t)rdata[3] << 12)         // temp_msb (0xFA)
+						| ((int32_t)rdata[4] << 4)        // temp_lsb (0xFB)
+						| ((int32_t)rdata[5] >> 4);       // temp_xlsb (0xFC)
+
+					m_readout_state = COMPENSATE_TEMPERATURE;
+					break;
+
+				default:
+					// should never happen
+					while(1);
+					break;
+			}
+			break;
+
+		case I2C_DMA_EVT_TIMEOUT:
+		case I2C_DMA_EVT_NAK:
+			m_readout_state = ERROR;
+			break;
+	}
+}
+
+
+bool bmp280_loop(void)
+{
+	bool retval = false;
+
+	switch(m_readout_state) {
+		case READY:
+			// nothing to do in this state
+			break;
+
+		case SEND_REQUEST:
+		case WAIT_MEASUREMENT_COMPLETE:
+		case READ_RESULTS:
+			// handled in cb_i2c_dma exclusively
+			break;
+
+		case COMPENSATE_TEMPERATURE:
+			m_last_temperature = bmp280_comp_temperature(m_temp_raw);
+			m_readout_state = COMPENSATE_PRESSURE;
+			break;
+
+		case COMPENSATE_PRESSURE:
+			m_last_pressure = bmp280_comp_pressure(m_press_raw);
+			m_readout_state = READY;
+			m_measurements_valid = true;
+			retval = true; // measurement complete
+			break;
+
+		case ERROR:
+			m_readout_state = READY;
+			m_measurements_valid = false;
+			retval = true; // measurement cycle terminated
+			break;
+	}
+
+	if(m_readout_state != READY) {
+		i2c_dma_loop();
+	}
+
+	return retval;
+}
+
+
+bool bmp280_start_measurement(void)
+{
+	uint8_t wdata[2];
+	uint8_t wsize = 0;
+
+	if(m_readout_state != READY) {
+		return false; // still busy
+	}
+
+	wdata[wsize++] = 0xF4; // measurement control register
+	wdata[wsize++] = (0x01 << 5) | (0x01 << 2) | 0x01; // pressure x1, temp x1, forced mode
+
+	i2c_dma_start_transfer7(I2C1, BMP280_7BIT_ADDR, wdata, wsize, 0);
+
+	m_readout_state = SEND_REQUEST;
+
+	return true;
+}
+
+
+bool bmp280_are_measurements_valid(void)
+{
+	return m_measurements_valid;
+}
+
+
+fxp_t bmp280_get_temperature(void)
+{
+	return m_last_temperature;
+}
+
+
+fxp_t bmp280_get_pressure(void)
+{
+	return m_last_pressure;
+}

src/bmp280.h

@@ -0,0 +1,18 @@
+#ifndef BMP280_H
+#define BMP280_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <fxp.h>
+
+bool bmp280_init(void);
+bool bmp280_loop(void); // returns true when measurement cycle has terminated (successfully or with error)
+
+bool bmp280_start_measurement(void);
+
+bool bmp280_are_measurements_valid(void);
+fxp_t bmp280_get_temperature(void);
+fxp_t bmp280_get_pressure(void);
+
+#endif // BMP280_H

src/bmp280_comp.c

@@ -0,0 +1,77 @@
+/* BMP280 value compensation code, from the datasheet. */
+
+#include "bmp280_comp.h"
+
+// calibration value cache. Values are set externally in bmp280.c
+
+uint16_t dig_T1;
+ int16_t dig_T2;
+ int16_t dig_T3;
+
+uint16_t dig_P1;
+ int16_t dig_P2;
+ int16_t dig_P3;
+ int16_t dig_P4;
+ int16_t dig_P5;
+ int16_t dig_P6;
+ int16_t dig_P7;
+ int16_t dig_P8;
+ int16_t dig_P9;
+
+
+typedef int32_t  BMP280_S32_t;
+typedef uint32_t BMP280_U32_t;
+typedef int64_t  BMP280_S64_t;
+
+
+// Returns temperature in DegC, resolution is 0.01 DegC. Output value of “5123” equals 51.23 DegC.
+// t_fine carries fine temperature as global value
+BMP280_S32_t t_fine;
+
+static BMP280_S32_t bmp280_compensate_T_int32(BMP280_S32_t adc_T)
+{
+	BMP280_S32_t var1, var2, T;
+	var1 = ((((adc_T>>3) - ((BMP280_S32_t)dig_T1<<1))) * ((BMP280_S32_t)dig_T2)) >> 11;
+	var2 = (((((adc_T>>4) - ((BMP280_S32_t)dig_T1)) * ((adc_T>>4) - ((BMP280_S32_t)dig_T1))) >> 12) * ((BMP280_S32_t)dig_T3)) >> 14;
+	t_fine = var1 + var2;
+	T = (t_fine * 5 + 128) >> 8;
+	return T;
+}
+
+// Returns pressure in Pa as unsigned 32 bit integer in Q24.8 format (24 integer bits and 8 fractional bits).
+// Output value of “24674867” represents 24674867/256 = 96386.2 Pa = 963.862 hPa
+static BMP280_U32_t bmp280_compensate_P_int64(BMP280_S32_t adc_P)
+{
+	BMP280_S64_t var1, var2, p;
+	var1 = ((BMP280_S64_t)t_fine) - 128000;
+	var2 = var1 * var1 * (BMP280_S64_t)dig_P6;
+	var2 = var2 + ((var1*(BMP280_S64_t)dig_P5)<<17);
+	var2 = var2 + (((BMP280_S64_t)dig_P4)<<35);
+	var1 = ((var1 * var1 * (BMP280_S64_t)dig_P3)>>8) + ((var1 * (BMP280_S64_t)dig_P2)<<12);
+	var1 = (((((BMP280_S64_t)1)<<47)+var1))*((BMP280_S64_t)dig_P1)>>33;
+	if (var1 == 0) {
+		return 0; // avoid exception caused by division by zero
+	}
+	p = 1048576-adc_P;
+	p = (((p<<31)-var2)*3125)/var1;
+	var1 = (((BMP280_S64_t)dig_P9) * (p>>13) * (p>>13)) >> 25;
+	var2 = (((BMP280_S64_t)dig_P8) * p) >> 19;
+	p = ((p + var1 + var2) >> 8) + (((BMP280_S64_t)dig_P7)<<4);
+	return (BMP280_U32_t)p;
+}
+
+
+
+fxp_t bmp280_comp_temperature(int32_t adc)
+{
+	int32_t compensated = bmp280_compensate_T_int32(adc);
+
+	return ((fxp_t)compensated << POINTPOS) / 100L;
+}
+
+fxp_t bmp280_comp_pressure(int32_t adc)
+{
+	uint32_t compensated = bmp280_compensate_P_int64(adc);
+
+	return (fxp_t)(((uint64_t)compensated << (POINTPOS - 8L)) / 100);
+}

src/bmp280_comp.h

@@ -0,0 +1,23 @@
+#ifndef BMP280_COMP_H
+#define BMP280_COMP_H
+
+#include <stdint.h>
+
+#include <fxp.h>
+
+/*!@brief Calculate temperature from BMP280 raw sensor value.
+ * @returns The temperature in °C.
+ */
+fxp_t bmp280_comp_temperature(int32_t adc);
+
+/*!@brief Calculate relative humidity from BMP280 raw sensor value.
+ * @returns The relative humidity in %.
+ */
+fxp_t bmp280_comp_humidity(int32_t adc);
+
+/*!@brief Calculate pressure from BMP280 raw sensor value.
+ * @returns The pressure in hPa.
+ */
+fxp_t bmp280_comp_pressure(int32_t adc);
+
+#endif // BMP280_COMP_H

src/charge_control.c

@@ -2,29 +2,33 @@
 
 #include <fxp.h>
 
+#include "bmp280.h"
 #include "power_switch.h"
 #include "measurement.h"
 #include "charge_pump.h"
 #include "rs485.h"
 #include "flash_config.h"
+#include "addon_io.h"
 
 #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",
-	"OVERCURRENT"
+	"OVERCURRENT",
+	"OVERCURRENT_DELAY"
 };
 
 static enum ChargeState charge_state;
@@ -52,13 +56,19 @@ static fxp_t u_bat_load_on;
 static fxp_t u_bat_load_off;
 
 static fxp_t load_current_limit;
+static fxp_t load_current_limit_delay;
 
 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;
 
+static uint32_t overload_retry_time;
+
 
 static enum ChargeState control_solar_charging(
 		fxp_t corridor_high,
@@ -86,9 +96,15 @@ 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 +211,7 @@ 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 +233,7 @@ 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 +244,27 @@ 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();
+
+				// switch on the heater via the isolated I/O addon board
+				addon_io_iso_out_on(0);
+			}
+
+			// 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;
+
+				// switch the heater off again when this state is left
+				addon_io_iso_out_off(0);
+				break;
+			}
+			break;
+
+
 		default:
 			// unknown state
 			break;
@@ -261,7 +298,20 @@ static void load_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 
 			if((meas->i_load > load_current_limit)
 					&& (discharge_time_in_state > FLASH_CONFIG_LOAD_CURRENT_INRUSH_TIME)) {
-				discharge_state = DISCHARGE_OVERCURRENT;
+				if(load_current_limit_delay == 0) {
+					// switch off immediately
+					power_switch_load_off();
+					discharge_state = DISCHARGE_OVERCURRENT;
+				} else {
+					discharge_state = DISCHARGE_OVERCURRENT_DELAY;
+				}
+			}
+
+			if((overload_retry_time != FLASH_CONFIG_OVERLOAD_RETRY_TIME) &&
+					(discharge_time_in_state > 300000)) {
+				// overload did not trigger for 5 minutes, so we assume it’s stable and
+				// reset the retry time delay.
+				overload_retry_time = FLASH_CONFIG_OVERLOAD_RETRY_TIME;
 			}
 
 			if(meas->avg_u_bat < u_bat_load_off) {
@@ -278,17 +328,36 @@ static void load_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 			// Can only switch on again after a specific amount of time has passed
 			if((meas->avg_u_bat > u_bat_load_on)
 					&& (discharge_time_in_state > FLASH_CONFIG_LOAD_ON_DELAY)) {
+				discharge_state = DISCHARGE_WAIT_CHARGEPUMP;
+			}
+			break;
+
+		case DISCHARGE_OVERCURRENT_DELAY:
+			if(meas->i_load < load_current_limit) {
+				// current recovered
 				discharge_state = DISCHARGE_OK;
+			} else if(discharge_time_in_state >= FLASH_CONFIG_OVERLOAD_DELAY_TIME) {
+				// switch off immediately
+				power_switch_load_off();
+				discharge_state = DISCHARGE_OVERCURRENT;
 			}
 			break;
 
 		case DISCHARGE_OVERCURRENT:
-			// Battery voltage is too low, so keep the load switched off
+			// Current limit reached
 			if(discharge_state_entered) {
 				power_switch_load_off();
 			}
 
-			// no way out except reset
+			// Overload recovery
+			if(discharge_time_in_state >= overload_retry_time) {
+				// double the overload retry time for the next turn if it is less than 7 days
+				if(overload_retry_time < (7*24*3600*1000)) {
+					overload_retry_time *= 2;
+				}
+
+				discharge_state = DISCHARGE_WAIT_CHARGEPUMP;
+			}
 			break;
 
 		default:
@@ -329,8 +398,13 @@ 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));
+
+	overload_retry_time = FLASH_CONFIG_OVERLOAD_RETRY_TIME;
 }
 
 
@@ -381,7 +455,8 @@ 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 +465,8 @@ 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;
 

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 +26,10 @@ enum DischargeState
 	DISCHARGE_WAIT_CHARGEPUMP,
 	DISCHARGE_OK,
 	DISCHARGE_VOLTAGE_LOW,
-	DISCHARGE_OVERCURRENT
+	DISCHARGE_OVERCURRENT,
+	DISCHARGE_OVERCURRENT_DELAY,
+
+	DISCHARGE_NUM_STATES
 };
 
 // Error flags

src/clock.c

@@ -1,6 +1,7 @@
 #include <libopencm3/stm32/rcc.h>
 
 #include "clock.h"
+#include "libopencm3/stm32/f0/rcc.h"
 
 void init_clock(void)
 {
@@ -26,6 +27,9 @@ void init_clock(void)
 
 	// DMA1 is used for ADC data transfer
 	rcc_periph_clock_enable(RCC_DMA1);
+
+	// I2C1 is used for communication with the BMP280
+	rcc_periph_clock_enable(RCC_I2C1);
 }
 
 

src/flash_config.c

@@ -3,5 +3,5 @@
 bool flash_config_is_present(void)
 {
 	return (FLASH_CONFIG_CAL_FACTOR_U_BAT != 0xFFFF)
-		&& (FLASH_CONFIG_U_BAT_REGULATION_CORRIDOR != -1);
+		&& (FLASH_CONFIG_DEEPSLEEP_DURATION != 0xFFFFFFFF);
 }

src/flash_config.h

@@ -63,27 +63,47 @@ extern uint8_t __conf_start;
 /* Resume operation below this temperature (in units of 0.1 °C). */
 #define FLASH_CONFIG_INTERNAL_TEMPERATURE_RECOVERY (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x012C))
 
+/* Minimum allowed external (BMP280) temperature (in units of 0.1 °C). If the
+ * temperature falls below this value, charging is stopped to prevent damage to
+ * the battery. */
+#define FLASH_CONFIG_EXTERNAL_TEMPERATURE_LIMIT (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0130))
+
+/* Resume operation above this temperature (in units of 0.1 °C). */
+#define FLASH_CONFIG_EXTERNAL_TEMPERATURE_RECOVERY (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0134))
+
 
 /* Thresholds for load control */
 
 /* Voltage above which the load is turned on (in mV). */
-#define FLASH_CONFIG_U_BAT_LOAD_ON (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0130))
+#define FLASH_CONFIG_U_BAT_LOAD_ON (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0138))
 /* Voltage below which the load is turned off (in mV). */
-#define FLASH_CONFIG_U_BAT_LOAD_OFF (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0134))
+#define FLASH_CONFIG_U_BAT_LOAD_OFF (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x013c))
 
 /* Current at which the overload protection triggers (in mA). */
-#define FLASH_CONFIG_LOAD_CURRENT_LIMIT_MA (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0138))
+#define FLASH_CONFIG_LOAD_CURRENT_LIMIT_MA (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0140))
 
 /* Inrush tolerance time (in ms). Overload protection is not enforced for this
  * time after load power-on. */
-#define FLASH_CONFIG_LOAD_CURRENT_INRUSH_TIME (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x013C))
+#define FLASH_CONFIG_LOAD_CURRENT_INRUSH_TIME (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0144))
+
+/* Inrush tolerance time (in ms). Overload protection is not enforced for this
+ * time after load power-on. */
+#define FLASH_CONFIG_LOAD_CURRENT_INRUSH_TIME (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0144))
 
 /* Minimum voltage that the charge pump must produce above U_bat before any
  * power FET is switched on (in mV). */
-#define FLASH_CONFIG_MIN_CHARGE_PUMP_EXCESS_VOLTAGE (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0140))
+#define FLASH_CONFIG_MIN_CHARGE_PUMP_EXCESS_VOLTAGE (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0148))
 
 /* The minimum time the load must be off before it can be switched on again (in ms). */
-#define FLASH_CONFIG_LOAD_ON_DELAY (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0144))
+#define FLASH_CONFIG_LOAD_ON_DELAY (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x014c))
+
+/* Overload delay time (in ms). If load current is too high for this duration,
+ * load is switched permanently off. */
+#define FLASH_CONFIG_OVERLOAD_DELAY_TIME (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0170))
+
+/* Overload retry time (in ms). Load is switched on again after this time if
+ * overload condition has triggered. */
+#define FLASH_CONFIG_OVERLOAD_RETRY_TIME (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0174))
 
 
 /* Measurement Averaging:
@@ -99,21 +119,23 @@ extern uint8_t __conf_start;
  * */
 
 /* Averaging factor for load current. */
-#define FLASH_CONFIG_AVG_ALPHA_I_SOLAR (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0148))
-#define FLASH_CONFIG_AVG_ALPHA_I_LOAD (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x014C))
-#define FLASH_CONFIG_AVG_ALPHA_U_BAT (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0150))
-#define FLASH_CONFIG_AVG_ALPHA_U_SW (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0154))
-#define FLASH_CONFIG_AVG_ALPHA_U_SOLAR (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0158))
-#define FLASH_CONFIG_AVG_ALPHA_TEMP (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x015C))
+#define FLASH_CONFIG_AVG_ALPHA_I_SOLAR (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0150))
+#define FLASH_CONFIG_AVG_ALPHA_I_LOAD (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0154))
+#define FLASH_CONFIG_AVG_ALPHA_U_BAT (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0158))
+#define FLASH_CONFIG_AVG_ALPHA_U_SW (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x015c))
+#define FLASH_CONFIG_AVG_ALPHA_U_SOLAR (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0160))
+#define FLASH_CONFIG_AVG_ALPHA_TEMP (*(int32_t*)(FLASH_CONFIG_BASE_PTR + 0x0164))
 
 
 /* Generic configuration */
 
 /* Time (in ms) to stay active in idle state before entering deep sleep. */
-#define FLASH_CONFIG_DEEPSLEEP_DELAY (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0160))
+#define FLASH_CONFIG_DEEPSLEEP_DELAY (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0168))
 
 /* Deep sleep duration (in seconds). */
-#define FLASH_CONFIG_DEEPSLEEP_DURATION (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x0164))
+#define FLASH_CONFIG_DEEPSLEEP_DURATION (*(uint32_t*)(FLASH_CONFIG_BASE_PTR + 0x016c))
+
+/* FIXME: next free memory location: 0x178. Update when adding a value! */
 
 
 /* Functions */

src/i2c_dma.c

@@ -0,0 +1,171 @@
+#include <string.h>
+
+#include <libopencm3/stm32/i2c.h>
+#include <libopencm3/stm32/dma.h>
+
+#include "i2c_dma.h"
+
+#define DMA_CHANNEL_TX DMA_CHANNEL2
+#define DMA_CHANNEL_RX DMA_CHANNEL3
+
+#define TIMEOUT_COUNTER_VALUE 100 // milliseconds
+
+static uint8_t m_wdata[2];
+static uint8_t m_wlen;
+static uint8_t m_rdata[32];
+static uint8_t m_rlen;
+
+static uint8_t m_addr;
+static uint32_t m_i2c;
+
+static uint32_t m_timeout_counter;
+
+typedef enum {
+	IDLE,
+	SEND_DATA,
+	RECEIVE_DATA
+} i2c_dma_state_t;
+
+static i2c_dma_state_t m_state;
+
+
+static i2c_dma_callback_t m_callback;
+
+static void setup_txdma(void)
+{
+	dma_channel_reset(DMA1, DMA_CHANNEL_TX);
+
+	dma_set_priority(DMA1, DMA_CHANNEL_TX, DMA_CCR_PL_LOW);
+	dma_set_memory_size(DMA1, DMA_CHANNEL_TX, DMA_CCR_MSIZE_8BIT);
+	dma_set_peripheral_size(DMA1, DMA_CHANNEL_TX, DMA_CCR_PSIZE_8BIT);
+	dma_enable_memory_increment_mode(DMA1, DMA_CHANNEL_TX);
+	dma_set_read_from_memory(DMA1, DMA_CHANNEL_TX);
+	dma_set_peripheral_address(DMA1, DMA_CHANNEL_TX, (uint32_t) &I2C_TXDR(m_i2c));
+
+	// send m_wlen bytes from m_wdata
+	dma_set_memory_address(DMA1, DMA_CHANNEL_TX, (uint32_t)m_wdata);
+	dma_set_number_of_data(DMA1, DMA_CHANNEL_TX, m_wlen);
+
+	dma_enable_channel(DMA1, DMA_CHANNEL_TX);
+
+	i2c_enable_txdma(m_i2c);
+}
+
+
+static void setup_rxdma(void)
+{
+	dma_channel_reset(DMA1, DMA_CHANNEL_RX);
+
+	dma_set_priority(DMA1, DMA_CHANNEL_RX, DMA_CCR_PL_LOW);
+	dma_set_memory_size(DMA1, DMA_CHANNEL_RX, DMA_CCR_MSIZE_8BIT);
+	dma_set_peripheral_size(DMA1, DMA_CHANNEL_RX, DMA_CCR_PSIZE_8BIT);
+	dma_enable_memory_increment_mode(DMA1, DMA_CHANNEL_RX);
+	dma_set_read_from_peripheral(DMA1, DMA_CHANNEL_RX);
+	dma_set_peripheral_address(DMA1, DMA_CHANNEL_RX, (uint32_t) &I2C_RXDR(m_i2c));
+
+	// receive m_rlen bytes and store them in m_rdata
+	dma_set_memory_address(DMA1, DMA_CHANNEL_RX, (uint32_t)m_rdata);
+	dma_set_number_of_data(DMA1, DMA_CHANNEL_RX, m_rlen);
+
+	dma_enable_channel(DMA1, DMA_CHANNEL_RX);
+
+	i2c_enable_rxdma(m_i2c);
+}
+
+
+void i2c_dma_init(i2c_dma_callback_t callback)
+{
+	m_callback = callback;
+
+	m_state = IDLE;
+}
+
+
+void i2c_dma_loop(void)
+{
+	switch(m_state) {
+		case IDLE:
+			// nothing to do
+			return;
+
+		case SEND_DATA:
+			//if(i2c_transfer_complete(m_i2c)) { // does not work for some reason :(
+			if(dma_get_interrupt_flag(DMA1, DMA_CHANNEL_TX, DMA_TCIF)) {
+				dma_clear_interrupt_flags(DMA1, DMA_CHANNEL_TX, DMA_TCIF);
+
+				if(m_rlen) {
+					m_state = RECEIVE_DATA;
+
+					i2c_set_7bit_address(m_i2c, m_addr);
+					i2c_set_read_transfer_dir(m_i2c);
+					i2c_set_bytes_to_transfer(m_i2c, m_rlen);
+					i2c_send_start(m_i2c);
+					i2c_enable_autoend(m_i2c); // important to do it after start() for a proper repeated start!
+					setup_rxdma();
+				} else {
+					// no RX requested => we are done here
+					m_state = IDLE;
+					m_callback(I2C_DMA_EVT_TRANSFER_COMPLETE, NULL, 0);
+				}
+			}
+
+			if(I2C_ISR(m_i2c) & I2C_ISR_NACKF) {
+				// there should be no NACK during the transfer => abort
+				I2C_ICR(m_i2c) |= I2C_ICR_NACKCF; // clear the interrupt flag
+				m_state = IDLE;
+				m_callback(I2C_DMA_EVT_NAK, NULL, 0);
+			}
+			break;
+
+		case RECEIVE_DATA:
+			//if(i2c_transfer_complete(m_i2c)) { // does not work for some reason :(
+			if(dma_get_interrupt_flag(DMA1, DMA_CHANNEL_RX, DMA_TCIF)) {
+				dma_clear_interrupt_flags(DMA1, DMA_CHANNEL_RX, DMA_TCIF);
+
+				m_state = IDLE;
+				m_callback(I2C_DMA_EVT_TRANSFER_COMPLETE, m_rdata, m_rlen);
+			}
+
+			if(I2C_ISR(m_i2c) & I2C_ISR_NACKF) {
+				// there should be no NACK during the transfer => abort
+				I2C_ICR(m_i2c) |= I2C_ICR_NACKCF; // clear the interrupt flag
+				m_state = IDLE;
+				m_callback(I2C_DMA_EVT_NAK, NULL, 0);
+			}
+			break;
+	}
+
+	m_timeout_counter--;
+	if(m_timeout_counter == 0) {
+		m_callback(I2C_DMA_EVT_TIMEOUT, NULL, 0);
+	}
+}
+
+
+void i2c_dma_start_transfer7(uint32_t i2c, uint8_t addr, const uint8_t *w, size_t wn, size_t rn)
+{
+	m_wlen = wn;
+	m_rlen = rn;
+
+	memcpy(m_wdata, w, wn);
+
+	m_state = SEND_DATA;
+
+	m_i2c = i2c;
+	m_addr = addr;
+
+	i2c_set_7bit_address(i2c, addr);
+	i2c_set_write_transfer_dir(i2c);
+	i2c_set_bytes_to_transfer(i2c, wn);
+
+	if(rn) {
+		i2c_disable_autoend(i2c); // prepare repeated start
+	} else {
+		i2c_enable_autoend(i2c); // stop condition after write transfer
+	}
+
+	m_timeout_counter = TIMEOUT_COUNTER_VALUE;
+
+	i2c_send_start(i2c); // start the transfer. The rest is handled by the DMA.
+	setup_txdma();
+}

src/i2c_dma.h

@@ -0,0 +1,22 @@
+#ifndef I2C_DMA_H
+#define I2C_DMA_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef enum
+{
+	I2C_DMA_EVT_TRANSFER_COMPLETE,
+	I2C_DMA_EVT_NAK,
+	I2C_DMA_EVT_TIMEOUT,
+} i2c_dma_evt_t;
+
+typedef void (*i2c_dma_callback_t)(i2c_dma_evt_t evt, const uint8_t *rdata, size_t rlen);
+
+void i2c_dma_init(i2c_dma_callback_t callback);
+
+void i2c_dma_loop(void);
+
+void i2c_dma_start_transfer7(uint32_t i2c, uint8_t addr, const uint8_t *w, size_t wn, size_t rn);
+
+#endif // I2C_DMA_H

src/main.c

@@ -16,12 +16,19 @@
 #include "power_switch.h"
 #include "measurement.h"
 #include "deepsleep.h"
+#include "bmp280.h"
+#include "addon_io.h"
 
 #include "pinout.h"
 #include "flash_config.h"
 
 volatile int wait_frame = 1;
 
+static enum {
+	BMP280_NOT_PRESENT,
+	BMP280_IDLE,
+	BMP280_MEASURING,
+} bmp280_state;
 
 /* Set up systick to fire freq times per second */
 static void init_systick(int freq)
@@ -170,6 +177,18 @@ static void report_status(struct MeasurementResult *meas_data)
 	rs485_enqueue(":");
 
 	rs485_enqueue(charge_control_is_discharge_blocked() ? "1" : "0");
+
+	if(bmp280_state != BMP280_NOT_PRESENT
+			&& bmp280_are_measurements_valid()) {
+		rs485_enqueue(":");
+		fxp_format(bmp280_get_temperature(), number, 2);
+		rs485_enqueue(number);
+		rs485_enqueue(":");
+
+		fxp_format(bmp280_get_pressure(), number, 2);
+		rs485_enqueue(number);
+	}
+
 	rs485_enqueue("\n");
 }
 
@@ -208,6 +227,19 @@ static void report_averaged(struct MeasurementResult *meas_data)
 	rs485_enqueue(":");
 
 	rs485_enqueue(charge_control_is_discharge_blocked() ? "1" : "0");
+
+	if(bmp280_state != BMP280_NOT_PRESENT
+			&& bmp280_are_measurements_valid()) {
+		rs485_enqueue(":");
+
+		fxp_format(bmp280_get_temperature(), number, 2);
+		rs485_enqueue(number);
+		rs485_enqueue(":");
+
+		fxp_format(bmp280_get_pressure(), number, 2);
+		rs485_enqueue(number);
+	}
+
 	rs485_enqueue("\n");
 }
 
@@ -233,6 +265,29 @@ static void low_power_mode(uint32_t duration_sec)
 }
 
 
+static void handle_bmp280(uint64_t timebase_ms)
+{
+	switch(bmp280_state) {
+		case BMP280_NOT_PRESENT:
+			// do nothing
+			break;
+
+		case BMP280_IDLE:
+			if(timebase_ms % 1000 == 137) {
+				bmp280_start_measurement();
+				bmp280_state = BMP280_MEASURING;
+			}
+			break;
+
+		case BMP280_MEASURING:
+			if(timebase_ms % 10 == 0 && bmp280_loop()) {
+				bmp280_state = BMP280_IDLE;
+			}
+			break;
+	}
+}
+
+
 int main(void)
 {
 	//uint32_t cpuload = 0;
@@ -250,6 +305,7 @@ int main(void)
 	init_clock();
 	init_rtc();
 
+	addon_io_init();
 	rs485_init();
 	charge_pump_init();
 	power_switch_init();
@@ -259,6 +315,12 @@ int main(void)
 	led_chplex_init();
 	led_chplex_on(LED_CHPLEX_IDX_SOLAR_ON);
 
+	if(bmp280_init()) {
+		bmp280_state = BMP280_IDLE;
+	} else {
+		bmp280_state = BMP280_NOT_PRESENT;
+	}
+
 	init_systick(1000);
 
 	rs485_enqueue("LNSC-2420 v" VERSION " initialized.\n");
@@ -298,6 +360,9 @@ int main(void)
 				report_averaged(&meas_data);
 			}
 
+			// update BMP280
+			handle_bmp280(timebase_ms);
+
 			measurement_wait_for_completion();
 			measurement_finalize(&meas_data);
 
@@ -306,19 +371,24 @@ int main(void)
 			charge_control_update(timebase_ms, &meas_data);
 
 			// deep sleep control
-			if(charge_control_is_idle()) {
-				if(!charge_control_was_idle) {
-					charge_control_was_idle = true;
-					charge_control_idle_since = timebase_ms;
-				} else {
-					// charge control already idle
-					if((timebase_ms - charge_control_idle_since) > FLASH_CONFIG_DEEPSLEEP_DELAY) {
-						low_power_mode(FLASH_CONFIG_DEEPSLEEP_DURATION);
-						charge_control_was_idle = false;
+			if(bmp280_state != BMP280_MEASURING) { // general blockers
+				if(charge_control_is_idle()) {
+					if(!charge_control_was_idle) {
+						charge_control_was_idle = true;
+						charge_control_idle_since = timebase_ms;
+					} else {
+						// charge control already idle
+						if((timebase_ms - charge_control_idle_since) > FLASH_CONFIG_DEEPSLEEP_DELAY) {
+							low_power_mode(FLASH_CONFIG_DEEPSLEEP_DURATION);
+							charge_control_was_idle = false;
+
+							// correct the time base after deep sleep
+							timebase_ms += FLASH_CONFIG_DEEPSLEEP_DURATION * 1000;
+						}
 					}
+				} else {
+					charge_control_was_idle = false;
 				}
-			} else {
-				charge_control_was_idle = false;
 			}
 		}
 

src/measurement.c

@@ -7,7 +7,6 @@
 #include "pinout.h"
 
 #include "measurement.h"
-#include "calibration.h"
 #include "flash_config.h"
 
 #define ADC_NUM_CHANNELS 6
@@ -94,15 +93,15 @@ void measurement_init(void)
 
 	// Convert calibration factors to fixed-point numbers for direct use
 	calibration_factors[ANALOG_INPUT_U_BAT] =
-		fxp_div(FXP_FROM_INT(CAL_FACTOR_U_BAT), FXP_FROM_INT(1000));
+		fxp_div(FXP_FROM_INT(FLASH_CONFIG_CAL_FACTOR_U_BAT), FXP_FROM_INT(1000));
 	calibration_factors[ANALOG_INPUT_U_SOLAR] =
-		fxp_div(FXP_FROM_INT(CAL_FACTOR_U_SOLAR), FXP_FROM_INT(1000));
+		fxp_div(FXP_FROM_INT(FLASH_CONFIG_CAL_FACTOR_U_SOLAR), FXP_FROM_INT(1000));
 	calibration_factors[ANALOG_INPUT_U_SW] =
-		fxp_div(FXP_FROM_INT(CAL_FACTOR_U_SW), FXP_FROM_INT(1000));
+		fxp_div(FXP_FROM_INT(FLASH_CONFIG_CAL_FACTOR_U_SW), FXP_FROM_INT(1000));
 	calibration_factors[ANALOG_INPUT_I_SOLAR] =
-		fxp_div(FXP_FROM_INT(CAL_FACTOR_I_SOLAR), FXP_FROM_INT(1000));
+		fxp_div(FXP_FROM_INT(FLASH_CONFIG_CAL_FACTOR_I_SOLAR), FXP_FROM_INT(1000));
 	calibration_factors[ANALOG_INPUT_I_LOAD] =
-		fxp_div(FXP_FROM_INT(CAL_FACTOR_I_LOAD), FXP_FROM_INT(1000));
+		fxp_div(FXP_FROM_INT(FLASH_CONFIG_CAL_FACTOR_I_LOAD), FXP_FROM_INT(1000));
 
 	// Convert and precalculate coefficients for exponential averaging
 	avg_alpha_i_solar = fxp_div(FXP_FROM_INT(FLASH_CONFIG_AVG_ALPHA_I_SOLAR), FXP_FROM_INT(1000));

src/pinout.h

@@ -43,4 +43,21 @@
 #define RS485_TX_PIN      GPIO6
 #define RS485_RX_PIN      GPIO7
 
+/*** Expansion connector signals ***/
+
+/* BMP280 I²C */
+
+#define BMP280_I2C_PORT   GPIOA
+
+#define BMP280_I2C_SCL    GPIO9
+#define BMP280_I2C_SDA    GPIO10
+
+/* Isolated inputs and outputs on I/O addon board */
+
+#define ADDON_ISO_IO_PORT       GPIOA
+
+#define ADDON_ISO_IO_OUT1       GPIO5
+#define ADDON_ISO_IO_OUT2       GPIO6
+#define ADDON_ISO_IO_IN         GPIO7
+
 #endif // PINOUT_H

utils/config_b26.yaml

@@ -56,13 +56,21 @@ config:
   # Resume operation below this temperature (in units of 0.1 °C).
   INTERNAL_TEMPERATURE_RECOVERY: 450
 
+  # Minimum allowed external (BMP280) temperature (in units of 0.1 °C). If the
+  # temperature falls below this value, charging is stopped to prevent damage to
+  # the battery.
+  EXTERNAL_TEMPERATURE_LIMIT: -30
+
+  # Resume operation above this temperature (in units of 0.1 °C).
+  EXTERNAL_TEMPERATURE_RECOVERY: 0
+
 
   # Thresholds for load control
 
   # Voltage above which the load is turned on (in mV).
   U_BAT_LOAD_ON: 27000
   # Voltage below which the load is turned off (in mV).
-  U_BAT_LOAD_OFF: 24000
+  U_BAT_LOAD_OFF: 24500
 
   # Current at which the overload protection triggers (in mA).
   LOAD_CURRENT_LIMIT_MA: 10000
@@ -71,6 +79,15 @@ config:
   # time after load power-on.
   LOAD_CURRENT_INRUSH_TIME: 10
 
+  # Overload delay time (in ms). If load current is too high for this duration,
+  # load is switched permanently off.
+  FLASH_CONFIG_OVERLOAD_DELAY_TIME: 10
+
+  # Overload retry time (in ms). Load is switched on again after this time if
+  # overload condition has triggered. If overload immediately triggers again,
+  # this time is doubled.
+  FLASH_CONFIG_OVERLOAD_RETRY_TIME: 10000
+
   # Minimum voltage that the charge pump must produce above U_bat before any
   # power FET is switched on (in mV).
   MIN_CHARGE_PUMP_EXCESS_VOLTAGE: 10000

utils/config_dev.yaml

@@ -56,6 +56,14 @@ config:
   # Resume operation below this temperature (in units of 0.1 °C).
   INTERNAL_TEMPERATURE_RECOVERY: 450
 
+  # Minimum allowed external (BMP280) temperature (in units of 0.1 °C). If the
+  # temperature falls below this value, charging is stopped to prevent damage to
+  # the battery.
+  EXTERNAL_TEMPERATURE_LIMIT: 250
+
+  # Resume operation above this temperature (in units of 0.1 °C).
+  EXTERNAL_TEMPERATURE_RECOVERY: 270
+
 
   # Thresholds for load control
 

utils/config_to_hex.py

@@ -29,20 +29,24 @@ CONFIG_KEY_TO_OFFSET = {
         "SLEEP_SWITCH_DELAY":               0x0124,
         "INTERNAL_TEMPERATURE_LIMIT":       0x0128,
         "INTERNAL_TEMPERATURE_RECOVERY":    0x012C,
-        "U_BAT_LOAD_ON":                    0x0130,
-        "U_BAT_LOAD_OFF":                   0x0134,
-        "LOAD_CURRENT_LIMIT_MA":            0x0138,
-        "LOAD_CURRENT_INRUSH_TIME":         0x013C,
-        "MIN_CHARGE_PUMP_EXCESS_VOLTAGE":   0x0140,
-        "LOAD_ON_DELAY":                    0x0144,
-        "AVG_ALPHA_I_SOLAR":                0x0148,
-        "AVG_ALPHA_I_LOAD":                 0x014C,
-        "AVG_ALPHA_U_BAT":                  0x0150,
-        "AVG_ALPHA_U_SW":                   0x0154,
-        "AVG_ALPHA_U_SOLAR":                0x0158,
-        "AVG_ALPHA_TEMP":                   0x015C,
-        "DEEPSLEEP_DELAY":                  0x0160,
-        "DEEPSLEEP_DURATION":               0x0164,
+        "EXTERNAL_TEMPERATURE_LIMIT":       0x0130,
+        "EXTERNAL_TEMPERATURE_RECOVERY":    0x0134,
+        "U_BAT_LOAD_ON":                    0x0138,
+        "U_BAT_LOAD_OFF":                   0x013c,
+        "LOAD_CURRENT_LIMIT_MA":            0x0140,
+        "LOAD_CURRENT_INRUSH_TIME":         0x0144,
+        "MIN_CHARGE_PUMP_EXCESS_VOLTAGE":   0x0148,
+        "LOAD_ON_DELAY":                    0x014c,
+        "AVG_ALPHA_I_SOLAR":                0x0150,
+        "AVG_ALPHA_I_LOAD":                 0x0154,
+        "AVG_ALPHA_U_BAT":                  0x0158,
+        "AVG_ALPHA_U_SW":                   0x015c,
+        "AVG_ALPHA_U_SOLAR":                0x0160,
+        "AVG_ALPHA_TEMP":                   0x0164,
+        "DEEPSLEEP_DELAY":                  0x0168,
+        "DEEPSLEEP_DURATION":               0x016c,
+        "FLASH_CONFIG_OVERLOAD_DELAY_TIME": 0x0170,
+        "FLASH_CONFIG_OVERLOAD_RETRY_TIME": 0x0174
     }
 
 
@@ -63,7 +67,7 @@ if __name__ == "__main__":
 
     for key, offset in CONFIG_KEY_TO_OFFSET.items():
         value = config['config'][key]
-        enc_bytes = struct.pack('<I', value)
+        enc_bytes = struct.pack('<i', value)
         output.puts(BASE_ADDR + offset, enc_bytes)
 
     output.write_hex_file(sys.argv[2])