Em2go: improve connection robustness (#29351)

charger/em2go-duo.go

@@ -101,9 +101,32 @@ func NewEm2GoDuo(ctx context.Context, uri string, slaveID uint8, connector int)
 		connector: connector,
 	}
 
+	b, err := wb.conn.ReadHoldingRegisters(em2GoDuoRegCommTimeout, 1)
+	if err != nil {
+		return nil, fmt.Errorf("failsafe timeout: %w", err)
+	}
+	if u := binary.BigEndian.Uint16(b); u > 0 {
+		go wb.heartbeat(ctx, time.Duration(u)*time.Second/2)
+	}
+
 	return wb, nil
 }
 
+// heartbeat keeps the Modbus connection alive to prevent the charger from
+// entering its failsafe state when the configured communication timeout expires.
+func (wb *Em2GoDuo) heartbeat(ctx context.Context, interval time.Duration) {
+	for tick := time.Tick(interval); ; {
+		select {
+		case <-tick:
+			if _, err := wb.conn.ReadHoldingRegisters(em2GoDuoRegSafeCurrent, 1); err != nil {
+				wb.log.ERROR.Println("heartbeat:", err)
+			}
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
 // Status implements the api.Charger interface
 func (wb *Em2GoDuo) Status() (api.ChargeStatus, error) {
 	b, err := wb.conn.ReadHoldingRegisters(em2GoDuoRegConnectorState, 1)

charger/em2go.go

@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/cenkalti/backoff/v4"
 	"github.com/evcc-io/evcc/api"
 	"github.com/evcc-io/evcc/util"
 	"github.com/evcc-io/evcc/util/modbus"
@@ -108,7 +109,42 @@ func NewEm2Go(ctx context.Context, uri string, slaveID uint8) (api.Charger, erro
 		current: 60,
 	}
 
-	return wb.initialize()
+	bo := backoff.WithContext(
+		backoff.NewExponentialBackOff(
+			backoff.WithInitialInterval(2*time.Second),
+			backoff.WithMaxInterval(10*time.Second),
+			backoff.WithMaxElapsedTime(30*time.Second),
+		), ctx)
+
+	res, err := backoff.RetryWithData(wb.initialize, bo)
+	if err != nil {
+		return nil, err
+	}
+
+	b, err := wb.conn.ReadHoldingRegisters(em2GoRegCommTimeout, 1)
+	if err != nil {
+		return nil, fmt.Errorf("failsafe timeout: %w", err)
+	}
+	if u := binary.BigEndian.Uint16(b); u > 0 {
+		go wb.heartbeat(ctx, time.Duration(u)*time.Second/2)
+	}
+
+	return res, nil
+}
+
+// heartbeat keeps the Modbus connection alive to prevent the charger from
+// entering its failsafe state when the configured communication timeout expires.
+func (wb *Em2Go) heartbeat(ctx context.Context, interval time.Duration) {
+	for tick := time.Tick(interval); ; {
+		select {
+		case <-tick:
+			if _, err := wb.conn.ReadHoldingRegisters(em2GoRegSafeCurrent, 1); err != nil {
+				wb.log.ERROR.Println("heartbeat:", err)
+			}
+		case <-ctx.Done():
+			return
+		}
+	}
 }
 
 // initialize performs common initialization for both Em2Go models