LoRa节点开发：5、代码详解LoRaWAN中的几种数据包（发送与接收数据）

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本文主要结合LoRaNode SDK v4.4.2和LoRaWAN规范1.0.3来展开。

1、数据包类型

LoRaWAN规范中有不同的数据包，通过MType字段区分，MType是3位的，总共可以表示8种不同类型的数据，其中前六种是不同的数据包，分别是“入网请求”、“入网回复”、“不需要确认上行数据包”、“需要确认上行数据包”、“不需要确认下行数据包”、“需要确认下行数据包”，后面两个一个是预留（RFU），一个开放给用户自定义（Proprietary）。

其中“入网请求”、“入网回复”，主要是用于OTAA入网的，在前面的LoRa节点开发——代码详解 LoRaWAN节点入网文章已经分析过了。

“不需要确认上行数据包”、“需要确认上行数据包”：主要用于用户上报数据。这里说一下不需要确认和需要确认，“需要确认”：就是发送数据后需要服务器回复一个ack，表明已经收到数据了，如果没有回复ack，那么还会重复发，一般用于紧急重要的数据上报；“不需要确认”：就是不管服务器有没有收到数据，发一次就不管了，一般用于非紧急不重要数据上报。

“不需要确认下行数据包”、“需要确认下行数据包”：主要服务器下发数据。不需要确认和需要确认同上面。服务器发送“需要确认”数据包时，需要节点回复ack给服务器。

2、源码分析

2.1上行数据

/*!* \brief   Prepares the payload of the frame*/
static void PrepareTxFrame( uint8_t port )
{switch( port ){case 2:{AppDataSizeBackup = AppDataSize = 1;AppDataBuffer[0] = AppLedStateOn;}break;case 224:if( ComplianceTest.LinkCheck == true ){ComplianceTest.LinkCheck = false;AppDataSize = 3;AppDataBuffer[0] = 5;AppDataBuffer[1] = ComplianceTest.DemodMargin;AppDataBuffer[2] = ComplianceTest.NbGateways;ComplianceTest.State = 1;}else{switch( ComplianceTest.State ){case 4:ComplianceTest.State = 1;break;case 1:AppDataSize = 2;AppDataBuffer[0] = ComplianceTest.DownLinkCounter >> 8;AppDataBuffer[1] = ComplianceTest.DownLinkCounter;break;}}break;default:break;}
}

可以看到，在PrepareTxFrame这个函数中，应用只需要在AppDataBuffer中填充相应的数据以及设置数据长度AppDataSize即可。

static bool SendFrame( void )
{McpsReq_t mcpsReq;LoRaMacTxInfo_t txInfo;if( LoRaMacQueryTxPossible( AppDataSize, &txInfo ) != LORAMAC_STATUS_OK ){// Send empty frame in order to flush MAC commandsmcpsReq.Type = MCPS_UNCONFIRMED;mcpsReq.Req.Unconfirmed.fBuffer = NULL;mcpsReq.Req.Unconfirmed.fBufferSize = 0;mcpsReq.Req.Unconfirmed.Datarate = LORAWAN_DEFAULT_DATARATE;}else{if( IsTxConfirmed == false ){mcpsReq.Type = MCPS_UNCONFIRMED;mcpsReq.Req.Unconfirmed.fPort = AppPort;mcpsReq.Req.Unconfirmed.fBuffer = AppDataBuffer;mcpsReq.Req.Unconfirmed.fBufferSize = AppDataSize;mcpsReq.Req.Unconfirmed.Datarate = LORAWAN_DEFAULT_DATARATE;}else{mcpsReq.Type = MCPS_CONFIRMED;mcpsReq.Req.Confirmed.fPort = AppPort;mcpsReq.Req.Confirmed.fBuffer = AppDataBuffer;mcpsReq.Req.Confirmed.fBufferSize = AppDataSize;mcpsReq.Req.Confirmed.NbTrials = 8;mcpsReq.Req.Confirmed.Datarate = LORAWAN_DEFAULT_DATARATE;}}// Update global variableAppData.MsgType = ( mcpsReq.Type == MCPS_CONFIRMED ) ? LORAMAC_HANDLER_CONFIRMED_MSG : LORAMAC_HANDLER_UNCONFIRMED_MSG;AppData.Port = mcpsReq.Req.Unconfirmed.fPort;AppData.Buffer = mcpsReq.Req.Unconfirmed.fBuffer;AppData.BufferSize = mcpsReq.Req.Unconfirmed.fBufferSize;LoRaMacStatus_t status;status = LoRaMacMcpsRequest( &mcpsReq );printf( "\r\n###### ===== MCPS-Request ==== ######\r\n" );printf( "STATUS      : %s\r\n", MacStatusStrings[status] );if( status == LORAMAC_STATUS_OK ){return false;}return true;
}

一些紧急重要数据可以发送“需要确认数据包”，从SendFrame这个函数中，可以看出需要发送“需要确认数据包”的时候，只需把IsTxConfirmed这个参数设置true即可。

应用只需设置以上3个参数即可发送，数据准备好之后，就是协议栈组包了，LoRaMacMcpsRequest( &mcpsReq )这个函数正是发送数据组包的函数，组包之后就是加密，最后就是射频发送了。

2.2下行数据

过程刚好和发送数据相反（上行数据），先是射频接收，接收到数据之后解密，用户应用数据处理。

查看static void ProcessRadioRxDone( void )函数，可以看到使用switch case语句，通过macHdr.Bits.MType字段对接收到的数据包进行了区分，FRAME_TYPE_DATA_CONFIRMED_DOWN和FRAME_TYPE_DATA_UNCONFIRMED_DOWN正是服务器的下行数据。

LoRaWAN协议栈在处理的时候，使用了设置标志位，然后回调函数的方法来处理。若有下发数据，则将 MacCtx.MacFlags.Bits.McpsInd 设置为1，如下：

            // Provide always an indication, skip the callback to the user application,// in case of a confirmed downlink retransmission.MacCtx.MacFlags.Bits.McpsInd = 1;

协议栈中，也给了英文注释，跳转到应用回调函数。

在LoRaWAN协议栈初始化的时候，注册了几个函数，然后在满足条件的时候回调。

int main( void )
{…………//代码过长，部分代码未截取macPrimitives.MacMcpsConfirm = McpsConfirm;macPrimitives.MacMcpsIndication = McpsIndication;macPrimitives.MacMlmeConfirm = MlmeConfirm;macPrimitives.MacMlmeIndication = MlmeIndication;macCallbacks.GetBatteryLevel = BoardGetBatteryLevel;macCallbacks.GetTemperatureLevel = NULL;macCallbacks.NvmContextChange = NvmCtxMgmtEvent;macCallbacks.MacProcessNotify = OnMacProcessNotify;LoRaMacInitialization( &macPrimitives, &macCallbacks, ACTIVE_REGION );…………//代码过长，部分代码未截取
}

其中，MlmeIndication就是下发回调函数。

查看MlmeIndication函数，如下：

static void McpsIndication( McpsIndication_t *mcpsIndication )
{printf( "\r\n###### ===== MCPS-Indication ==== ######\r\n" );printf( "STATUS      : %s\r\n", EventInfoStatusStrings[mcpsIndication->Status] );if( mcpsIndication->Status != LORAMAC_EVENT_INFO_STATUS_OK ){return;}switch( mcpsIndication->McpsIndication ){case MCPS_UNCONFIRMED:{break;}case MCPS_CONFIRMED:{break;}case MCPS_PROPRIETARY:{break;}case MCPS_MULTICAST:{break;}default:break;}// Check Multicast// Check Port// Check Datarate// Check FramePendingif( mcpsIndication->FramePending == true ){// The server signals that it has pending data to be sent.// We schedule an uplink as soon as possible to flush the server.OnTxNextPacketTimerEvent( NULL );}// Check Buffer// Check BufferSize// Check Rssi// Check Snr// Check RxSlotif( ComplianceTest.Running == true ){ComplianceTest.DownLinkCounter++;}if( mcpsIndication->RxData == true ){switch( mcpsIndication->Port ){case 1: // The application LED can be controlled on port 1 or 2case 2:if( mcpsIndication->BufferSize == 1 ){AppLedStateOn = mcpsIndication->Buffer[0] & 0x01;}break;case 224:if( ComplianceTest.Running == false ){// Check compliance test enable command (i)if( ( mcpsIndication->BufferSize == 4 ) &&( mcpsIndication->Buffer[0] == 0x01 ) &&( mcpsIndication->Buffer[1] == 0x01 ) &&( mcpsIndication->Buffer[2] == 0x01 ) &&( mcpsIndication->Buffer[3] == 0x01 ) ){IsTxConfirmed = false;AppPort = 224;AppDataSizeBackup = AppDataSize;AppDataSize = 2;ComplianceTest.DownLinkCounter = 0;ComplianceTest.LinkCheck = false;ComplianceTest.DemodMargin = 0;ComplianceTest.NbGateways = 0;ComplianceTest.Running = true;ComplianceTest.State = 1;MibRequestConfirm_t mibReq;mibReq.Type = MIB_ADR;mibReq.Param.AdrEnable = true;LoRaMacMibSetRequestConfirm( &mibReq );#if defined( REGION_EU868 ) || defined( REGION_RU864 ) || defined( REGION_CN779 ) || defined( REGION_EU433 )LoRaMacTestSetDutyCycleOn( false );
#endif}}else{ComplianceTest.State = mcpsIndication->Buffer[0];switch( ComplianceTest.State ){case 0: // Check compliance test disable command (ii)IsTxConfirmed = LORAWAN_CONFIRMED_MSG_ON;AppPort = LORAWAN_APP_PORT;AppDataSize = AppDataSizeBackup;ComplianceTest.DownLinkCounter = 0;ComplianceTest.Running = false;MibRequestConfirm_t mibReq;mibReq.Type = MIB_ADR;mibReq.Param.AdrEnable = LORAWAN_ADR_ON;LoRaMacMibSetRequestConfirm( &mibReq );
#if defined( REGION_EU868 ) || defined( REGION_RU864 ) || defined( REGION_CN779 ) || defined( REGION_EU433 )LoRaMacTestSetDutyCycleOn( LORAWAN_DUTYCYCLE_ON );
#endifbreak;case 1: // (iii, iv)AppDataSize = 2;break;case 2: // Enable confirmed messages (v)IsTxConfirmed = true;ComplianceTest.State = 1;break;case 3:  // Disable confirmed messages (vi)IsTxConfirmed = false;ComplianceTest.State = 1;break;case 4: // (vii)AppDataSize = mcpsIndication->BufferSize;AppDataBuffer[0] = 4;for( uint8_t i = 1; i < MIN( AppDataSize, LORAWAN_APP_DATA_MAX_SIZE ); i++ ){AppDataBuffer[i] = mcpsIndication->Buffer[i] + 1;}break;case 5: // (viii){MlmeReq_t mlmeReq;mlmeReq.Type = MLME_LINK_CHECK;LoRaMacStatus_t status = LoRaMacMlmeRequest( &mlmeReq );printf( "\r\n###### ===== MLME-Request - MLME_LINK_CHECK ==== ######\r\n" );printf( "STATUS      : %s\r\n", MacStatusStrings[status] );}break;case 6: // (ix){// Disable TestMode and revert back to normal operationIsTxConfirmed = LORAWAN_CONFIRMED_MSG_ON;AppPort = LORAWAN_APP_PORT;AppDataSize = AppDataSizeBackup;ComplianceTest.DownLinkCounter = 0;ComplianceTest.Running = false;MibRequestConfirm_t mibReq;mibReq.Type = MIB_ADR;mibReq.Param.AdrEnable = LORAWAN_ADR_ON;LoRaMacMibSetRequestConfirm( &mibReq );
#if defined( REGION_EU868 ) || defined( REGION_RU864 ) || defined( REGION_CN779 ) || defined( REGION_EU433 )LoRaMacTestSetDutyCycleOn( LORAWAN_DUTYCYCLE_ON );
#endifJoinNetwork( );}break;case 7: // (x){if( mcpsIndication->BufferSize == 3 ){MlmeReq_t mlmeReq;mlmeReq.Type = MLME_TXCW;mlmeReq.Req.TxCw.Timeout = ( uint16_t )( ( mcpsIndication->Buffer[1] << 8 ) | mcpsIndication->Buffer[2] );LoRaMacStatus_t status = LoRaMacMlmeRequest( &mlmeReq );printf( "\r\n###### ===== MLME-Request - MLME_TXCW ==== ######\r\n" );printf( "STATUS      : %s\r\n", MacStatusStrings[status] );}else if( mcpsIndication->BufferSize == 7 ){MlmeReq_t mlmeReq;mlmeReq.Type = MLME_TXCW_1;mlmeReq.Req.TxCw.Timeout = ( uint16_t )( ( mcpsIndication->Buffer[1] << 8 ) | mcpsIndication->Buffer[2] );mlmeReq.Req.TxCw.Frequency = ( uint32_t )( ( mcpsIndication->Buffer[3] << 16 ) | ( mcpsIndication->Buffer[4] << 8 ) | mcpsIndication->Buffer[5] ) * 100;mlmeReq.Req.TxCw.Power = mcpsIndication->Buffer[6];LoRaMacStatus_t status = LoRaMacMlmeRequest( &mlmeReq );printf( "\r\n###### ===== MLME-Request - MLME_TXCW1 ==== ######\r\n" );printf( "STATUS      : %s\r\n", MacStatusStrings[status] );}ComplianceTest.State = 1;}break;case 8: // Send DeviceTimeReq{MlmeReq_t mlmeReq;mlmeReq.Type = MLME_DEVICE_TIME;LoRaMacStatus_t status = LoRaMacMlmeRequest( &mlmeReq );printf( "\r\n###### ===== MLME-Request - MLME_DEVICE_TIME ==== ######\r\n" );printf( "STATUS      : %s\r\n", MacStatusStrings[status] );}break;default:break;}}break;default:break;}}// Switch LED 2 ON for each received downlinkGpioWrite( &Led2, 1 );TimerStart( &Led2Timer );const char *slotStrings[] = { "1", "2", "C", "C Multicast", "B Ping-Slot", "B Multicast Ping-Slot" };printf( "\r\n###### ===== DOWNLINK FRAME %lu ==== ######\r\n", mcpsIndication->DownLinkCounter );printf( "RX WINDOW   : %s\r\n", slotStrings[mcpsIndication->RxSlot] );printf( "RX PORT     : %d\r\n", mcpsIndication->Port );if( mcpsIndication->BufferSize != 0 ){printf( "RX DATA     : \r\n" );PrintHexBuffer( mcpsIndication->Buffer, mcpsIndication->BufferSize );}printf( "\r\n" );printf( "DATA RATE   : DR_%d\r\n", mcpsIndication->RxDatarate );printf( "RX RSSI     : %d\r\n", mcpsIndication->Rssi );printf( "RX SNR      : %d\r\n", mcpsIndication->Snr );printf( "\r\n" );
}

应用可以在这里获取服务器下发的数据，也可以获取到下发信号的RSSI和SNR等。

至此，如何上报数据，下发接收数据分析完成。

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推荐阅读：
LoRa节点开发——初识SDK
LoRa节点开发——构建keil工程
LoRa节点开发——SDK整体设计思路
LoRa节点开发——SDK整体设计思路

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