Add MuxTime to downlink messages.

The MuxTime is an alternative way to time-sync Basics Station gateways,
instead of using the timesync messages.

This is documented here:
https://lora-developers.semtech.com/build/software/lora-basics/lora-basics-for-gateways/?url=time.html

Author: brocaar

internal/backend/basicstation/backend_test.go

@@ -564,6 +564,9 @@ func (ts *BackendTestSuite) TestSendDownlinkFrame() {
 	rCtx := uint64(3)
 	xTime := uint64(4)
 
+	assert.NotNil(df.MuxTime)
+	df.MuxTime = nil
+
 	assert.Equal(structs.DownlinkFrame{
 		MessageType: structs.DownlinkMessage,
 		DevEui:      "01-01-01-01-01-01-01-01",

internal/backend/basicstation/structs/downlink_message.go

@@ -15,21 +15,22 @@ import (
 type DownlinkFrame struct {
 	MessageType MessageType `json:"msgtype"`
 
-	DevEui   string  `json:"DevEui"`
-	DC       int     `json:"dC"`
-	DIID     uint32  `json:"diid"`
-	PDU      string  `json:"pdu"`
-	Priority int     `json:"priority"`
-	RxDelay  *int    `json:"RxDelay,omitempty"`
-	RX1DR    *int    `json:"RX1DR,omitempty"`
-	RX1Freq  *uint32 `json:"RX1Freq,omitempty"`
-	RX2DR    *int    `json:"RX2DR,omitempty"`
-	RX2Freq  *uint32 `json:"RX2Freq,omitempty"`
-	DR       *int    `json:"DR,omitempty"`
-	Freq     *uint32 `json:"Freq,omitempty"`
-	GPSTime  *uint64 `json:"gpstime,omitempty"`
-	XTime    *uint64 `json:"xtime,omitempty"`
-	RCtx     *uint64 `json:"rctx,omitempty"`
+	DevEui   string   `json:"DevEui"`
+	DC       int      `json:"dC"`
+	DIID     uint32   `json:"diid"`
+	PDU      string   `json:"pdu"`
+	Priority int      `json:"priority"`
+	RxDelay  *int     `json:"RxDelay,omitempty"`
+	RX1DR    *int     `json:"RX1DR,omitempty"`
+	RX1Freq  *uint32  `json:"RX1Freq,omitempty"`
+	RX2DR    *int     `json:"RX2DR,omitempty"`
+	RX2Freq  *uint32  `json:"RX2Freq,omitempty"`
+	DR       *int     `json:"DR,omitempty"`
+	Freq     *uint32  `json:"Freq,omitempty"`
+	GPSTime  *uint64  `json:"gpstime,omitempty"`
+	XTime    *uint64  `json:"xtime,omitempty"`
+	RCtx     *uint64  `json:"rctx,omitempty"`
+	MuxTime  *float64 `json:"MuxTime,omitempty"`
 }
 
 // DownlinkFrameFromProto convers the given protobuf message to a DownlinkFrame.
@@ -38,6 +39,9 @@ func DownlinkFrameFromProto(loraBand band.Band, pb *gw.DownlinkFrame) (DownlinkF
 		return DownlinkFrame{}, errors.New("items must contain at least one item")
 	}
 
+	// MuxTime
+	muxTime := float64(time.Now().UnixMicro()) / 1000000
+
 	// We assume this is for RX1
 	item := pb.Items[0]
 
@@ -47,6 +51,7 @@ func DownlinkFrameFromProto(loraBand band.Band, pb *gw.DownlinkFrame) (DownlinkF
 		DevEui:      "01-01-01-01-01-01-01-01", // set to fake DevEUI (setting it to 0 causes the BasicStation to not send acks, see https://github.com/lorabasics/basicstation/issues/71).
 		DIID:        pb.DownlinkId,
 		PDU:         hex.EncodeToString(item.PhyPayload),
+		MuxTime:     &muxTime,
 	}
 
 	// context

internal/backend/basicstation/structs/downlink_message_test.go

@@ -251,6 +251,8 @@ func TestDownlinkFrameFromProto(t *testing.T) {
 			if err != nil {
 				return
 			}
+			assert.NotNil(out.MuxTime)
+			out.MuxTime = nil
 			assert.Equal(tst.Out, out)
 		})
 	}

internal/backend/basicstation/structs/router_config.go

@@ -3,6 +3,7 @@ package structs
 import (
 	"encoding/binary"
 	"fmt"
+	"time"
 
 	"github.com/brocaar/chirpstack-gateway-bridge/internal/config"
 	"github.com/brocaar/chirpstack-gateway-bridge/internal/config/sx1301v1"
@@ -35,6 +36,7 @@ type RouterConfig struct {
 	FreqRange   []uint32     `json:"freq_range"`
 	DRs         [][]int      `json:"DRs"`
 	SX1301Conf  []SX1301Conf `json:"sx1301_conf"`
+	MuxTime     *float64     `json:"MuxTime,omitempty"`
 }
 
 // SX1301Conf implements a single SX1301 configuration.
@@ -84,12 +86,16 @@ type SX1301ConfChanMultiSF struct {
 func GetRouterConfig(region band.Name, netIDs []lorawan.NetID, joinEUIs [][2]lorawan.EUI64, freqMin, freqMax uint32, concentrators []config.BasicStationConcentrator) (RouterConfig, error) {
 	concentratorCount := len(concentrators)
 
+	// MuxTime
+	muxTime := float64(time.Now().UnixMicro()) / 1000000
+
 	c := RouterConfig{
 		MessageType: RouterConfigMessage,
 		Region:      regionNameMapping[region],
 		HWSpec:      fmt.Sprintf("sx1301/%d", concentratorCount),
 		FreqRange:   []uint32{freqMin, freqMax},
 		SX1301Conf:  make([]SX1301Conf, concentratorCount),
+		MuxTime:     &muxTime,
 	}
 
 	// set NetID filter

internal/backend/basicstation/structs/router_config_test.go

@@ -321,6 +321,8 @@ func TestRouterConfig(t *testing.T) {
 			if err != nil {
 				return
 			}
+			assert.NotNil(rc.MuxTime)
+			rc.MuxTime = nil
 			assert.Equal(tst.ExpectedRouterConfig, rc)
 		})
 	}