succd: Fix -KEC1 relay board updates

The accesses to -KEC1 always time out on the attempt to update the
output values.  We noticed that this is related to the timing between
the reading of the inputs and the following write to the outputs.

Fix -KEC1 accesses by waiting before sending the next request to the
board after receiving the reply for the previous one.

succbone/succd/modbus.go

@@ -2,11 +2,10 @@ package main
 
 import (
 	"context"
-	"errors"
-	"fmt"
 	"time"
 
 	"github.com/simonvetter/modbus"
+	"k8s.io/klog"
 )
 
 func modbusValuesToFloat(v uint16) float32 {
@@ -39,7 +38,7 @@ func (d *daemon) modbusConnect() error {
 // There are currently two devices connected to the modbus.
 // The first one (slave 1) is a temperature/humidity sensor.
 // The second one (slave 2) is a PTA8D08 transmitter
-func (d *daemon) modbusUpdate() error {
+func (d *daemon) modbusUpdate() {
 	var err error
 
 	// Switch to slave 1 (BTA1)
@@ -49,18 +48,15 @@ func (d *daemon) modbusUpdate() error {
 	var registersBTA1 []uint16 // temperature, humidity
 	registersBTA1, err = d.modbusClient.ReadRegisters(1, 2, modbus.INPUT_REGISTER)
 	if err != nil {
-		return err
-	}
-
-	if len(registersBTA1) != 2 {
-		msg := fmt.Sprintf("Expected two registers from modbus slave 1, but got %d", len(registersBTA1))
-		return errors.New(msg)
-	}
-
+		klog.Warningf("error while reading registers from BTA1 %v", err)
+	} else if len(registersBTA1) != 2 {
+		klog.Warningf("expected two registers from modbus slave 1, but got %d", len(registersBTA1))
+	} else {
 		d.mu.Lock()
 		d.daemonState.tempSEM = modbusValuesToFloat(registersBTA1[0])
 		d.daemonState.humiditySEM = modbusValuesToFloat(registersBTA1[1])
 		d.mu.Unlock()
+	}
 
 	// Switch to slave 2 (KEC2)
 	d.modbusClient.SetUnitId(2)
@@ -72,18 +68,16 @@ func (d *daemon) modbusUpdate() error {
 	var registersKEC2 []uint16 // temperatures dp
 	registersKEC2, err = d.modbusClient.ReadRegisters(0, 3, modbus.HOLDING_REGISTER)
 	if err != nil {
-		return err
-	}
-
-	if len(registersKEC2) != 3 {
-		return fmt.Errorf("expected three registers from modbus slave 2, but got %d", len(registersKEC2))
-	}
-
+		klog.Warningf("error while reading registers from KEC2 %v", err)
+	} else if len(registersKEC2) != 3 {
+		klog.Warningf("expected three registers from modbus slave 2, but got %d", len(registersKEC2))
+	} else {
 		d.mu.Lock()
 		d.daemonState.tempDPBottom = modbusValuesToFloat(registersKEC2[0])
 		d.daemonState.tempDPInlet = modbusValuesToFloat(registersKEC2[1])
 		d.daemonState.tempDPTop = modbusValuesToFloat(registersKEC2[2])
 		d.mu.Unlock()
+	}
 
 	// Switch to slave 3 (KEC1)
 	d.modbusClient.SetUnitId(3)
@@ -94,8 +88,8 @@ func (d *daemon) modbusUpdate() error {
 
 	digitalInputRegisters, err = d.modbusClient.ReadRegisters(0x81, 8, modbus.HOLDING_REGISTER)
 	if err != nil {
-		return err
-	}
+		klog.Warningf("error while reading digital inputs from KEC1 %v", err)
+	} else {
 		// Convert MODBUS words into bools
 		for idx, value := range digitalInputRegisters {
 			if value != 0 {
@@ -105,6 +99,12 @@ func (d *daemon) modbusUpdate() error {
 			}
 		}
 		// TODO: Input mapping goes here
+	}
+
+	// We must wait between reading and writing to the -KEC1 relay board
+	// because otherwise it chokes and times out the write registers
+	// command.
+	time.Sleep(time.Millisecond * 10)
 
 	// KFA1-KFA8
 	var relayState [8]bool
@@ -140,10 +140,8 @@ func (d *daemon) modbusUpdate() error {
 
 	err = d.modbusClient.WriteRegisters(0x01, registerValuesKEC1[:])
 	if err != nil {
-		return err
+		klog.Warningf("error while updating registers %v", err)
 	}
-
-	return nil
 }
 
 // Call modbusUpdate every 100 milliseconds