charge_control: add extra state to fix initial charging

Before this change, initial charging ended exactly HOLD_TIME after the
CHARGE_INITIAL state was entered. This was usually not sufficient to
reach the INITIAL_FULL voltage. Now a new state is entered once the
INITIAL_FULL voltage is reached.

src/charge_control.c

@@ -13,6 +13,7 @@
 static const char *CHARGE_STATE_TEXT[] = {
 	"WAIT_CHARGEPUMP",
 	"INITIAL",
+	"INITIAL_HOLD",
 	"TRANSITION",
 	"FLOAT",
 	"SLEEP",
@@ -40,6 +41,8 @@ static fxp_t u_bat_regulation_corridor;
 static fxp_t u_bat_initial_full;
 static fxp_t u_bat_initial_low;
 
+static fxp_t u_bat_initial_hold_cancel;
+
 static fxp_t u_bat_float_full;
 static fxp_t u_bat_float_low;
 
@@ -127,7 +130,28 @@ static void solar_fsm_update(uint64_t uptime_ms, struct MeasurementResult *meas)
 					charge_state,
 					charge_time_in_state);
 
-			// time limit for initial charging
+			// switch to hold state when high threshold is reached
+			if(meas->u_bat >= u_bat_initial_full) {
+				charge_state = CHARGE_INITIAL_HOLD;
+			}
+
+			break;
+
+		case CHARGE_INITIAL_HOLD:
+			charge_state = control_solar_charging(
+					u_bat_initial_full,
+					u_bat_initial_low,
+					uptime_ms,
+					meas,
+					charge_state,
+					charge_time_in_state);
+
+			// cancel charge hold if battery voltage is below threshold
+			if(meas->u_bat <= u_bat_initial_hold_cancel) {
+				charge_state = CHARGE_INITIAL;
+			}
+
+			// time limit for initial hold charging
 			if(charge_time_in_state > INITIAL_CHARGE_HOLD_TIME) {
 				charge_state = CHARGE_TRANSITION;
 			}
@@ -295,6 +319,8 @@ void charge_control_init(void)
 	u_bat_initial_full = fxp_div(FXP_FROM_INT(U_BAT_INITIAL_FULL), FXP_FROM_INT(1000));
 	u_bat_initial_low  = fxp_sub(u_bat_initial_full, u_bat_regulation_corridor);
 
+	u_bat_initial_hold_cancel = fxp_div(FXP_FROM_INT(U_BAT_INITIAL_HOLD_CANCEL), FXP_FROM_INT(1000));
+
 	u_bat_float_full = fxp_div(FXP_FROM_INT(U_BAT_FLOAT_FULL), FXP_FROM_INT(1000));
 	u_bat_float_low  = fxp_sub(u_bat_float_full, u_bat_regulation_corridor);
 

src/charge_control.h

@@ -11,6 +11,7 @@ enum ChargeState
 {
 	CHARGE_WAIT_CHARGEPUMP,
 	CHARGE_INITIAL,
+	CHARGE_INITIAL_HOLD,
 	CHARGE_TRANSITION,
 	CHARGE_FLOAT,
 	CHARGE_SLEEP,

src/config.h

@@ -9,6 +9,9 @@
 /* Initial charge battery voltage threshold (in mV). */
 #define U_BAT_INITIAL_FULL    28600       // stop charging if battery voltage reaches this threshold
 
+/* Cancel initial charge voltage hold below this battery voltage (in mV). */
+#define U_BAT_INITIAL_HOLD_CANCEL    28000
+
 /* Transition to floating voltage levels after this time (in ms). */
 #define INITIAL_CHARGE_HOLD_TIME    3600000