代码基本移植官方GaiaControl Demo。
支持RWCP 断点续传 设置蓝牙mtu.协议。这里主要分析GAIA CSR ble ota的过程，协议等等，希望对你有所帮助。这里对蓝牙服务特性订阅都不谈。读者自行了解。

Gaia 是CSR 制定的一个上层使用协议，其在BR/EDR 基于RFCOMM，可以理解为一个特别UUID的SPP；经典蓝牙使用的UUID 0X1107。 ios只支持BLE所以重点关注SPP升级UUID 0X1101
Gaia 的UUID是00001107-D102-11E1-9B23-00025B00A5A5；
SPP 的UUID是00001101-0000-1000-8000-00805F9B34FB；
主要UUID如下

//升级服务UUID
Uuid otaUUID = Uuid.parse("00001100-d102-11e1-9b23-00025b00a5a5");
//升级服务订阅的特性
Uuid notifyUUID = Uuid.parse("00001102-d102-11e1-9b23-00025b00a5a5");
//升级服务写入特性
Uuid writeUUID = Uuid.parse("00001101-d102-11e1-9b23-00025b00a5a5");
//RWCP 更快的传输特性 不需要回包
Uuid writeNoResUUID = Uuid.parse("00001103-d102-11e1-9b23-00025b00a5a5");

GAIA协议流程非常繁琐，我们从头开始分析。
首先订阅升级通知通道 00001102-d102-11e1-9b23-00025b00a5a5
向00001101-d102-11e1-9b23-00025b00a5a5写入指令 0x000A400112 表示订阅升级通知
这里的000A400112组包格式如下

000A 4001 12

其中0x000A为固定字符vendorId 0x4001两个字节表示commandId 10x2表示订阅升级通知
订阅成功UUID 0x1102返回

000AC0010012

此时就可以开始发送升级请求

  void sendUpgradeConnect() async {GaiaPacketBLE packet = GaiaPacketBLE(GAIA.COMMAND_VM_UPGRADE_CONNECT);writeMsg(packet.getBytes());}

即发送0x0640 指令

000A0640

收到回包000A864000表示请求成功此时开始准备文件MD5信息用于校验 取文件MD5末尾4个字节。命令如下

000A0642130004F891C66F

这里的组包格式 vendorId + commandId + 操作符+数据 其中数据包含 长度+真正数据

000A 0642 13 0004 F891C66F

F891C66F为文件MD5;

此时会收到两条数据包

000A0642010000 //升级开始
000A40031214000600F891C66F03 //MD5接收完成 并携带上次传输步骤信息 其中0x03 表示正在升级并且上次传输步骤为0x00 

 void receiveSyncCFM(VMUPacket? packet) {List data = packet?.mData ?? [];if (data.length >= 6) {int step = data[0];addLog("上次传输步骤 step $step");if (step == ResumePoints.IN_PROGRESS) {setResumePoint(step);} else {mResumePoint = step;}} else {mResumePoint = ResumePoints.DATA_TRANSFER;}sendStartReq();}void sendStartReq() {VMUPacket packet = VMUPacket.get(OpCodes.UPGRADE_START_REQ);sendVMUPacket(packet, false);}

接下来就是组包发送数据

  void sendStartDataReq() {setResumePoint(ResumePoints.DATA_TRANSFER);VMUPacket packet = VMUPacket.get(OpCodes.UPGRADE_START_DATA_REQ);sendVMUPacket(packet, false);}000A0642150000

void receiveDataBytesREQ(VMUPacket? packet) {List data = packet?.mData ?? [];// Checking the data has the good lengthif (data.length == OpCodes.DATA_LENGTH) {// retrieving information from the received packet//REC 120300080000002400000000//SEND 000A064204000D0000030000FFFF0001FFFF0002var lengthByte = [data[0], data[1], data[2], data[3]];var fileByte = [data[4], data[5], data[6], data[7]];mBytesToSend = int.parse(StringUtils.byteToHexString(lengthByte), radix: 16);int fileOffset = int.parse(StringUtils.byteToHexString(fileByte), radix: 16);addLog(StringUtils.byteToHexString(data) + "本次发包: $fileOffset $mBytesToSend");// we check the value for the offsetmStartOffset += (fileOffset > 0 && fileOffset + mStartOffset < (mBytesFile?.length ?? 0)) ? fileOffset : 0;// if the asked length doesn't fit with possibilities we use the maximum length we can use.mBytesToSend = (mBytesToSend > 0) ? mBytesToSend : 0;// if the requested length will look for bytes out of the array we reduce it to the remaining length.int remainingLength = mBytesFile?.length ?? 0 - mStartOffset;mBytesToSend = (mBytesToSend < remainingLength) ? mBytesToSend : remainingLength;if (mIsRWCPEnabled.value) {while (mBytesToSend > 0) {sendNextDataPacket();}} else {addLog("receiveDataBytesREQ: sendNextDataPacket");sendNextDataPacket();}} else {addLog("UpgradeError 数据传输失败");abortUpgrade();}}

断点续传的逻辑也在这。读取到fileOffset 进行文件偏移

最后一包数据格式0x01 + 数据 发送完毕

void sendData(bool lastPacket, List data) {List dataToSend = [];dataToSend.add(lastPacket ? 0x01 : 0x00);dataToSend.addAll(data);sendPkgCount++;VMUPacket packet = VMUPacket.get(OpCodes.UPGRADE_DATA, data: dataToSend);sendVMUPacket(packet, true);}

收到是否提交 我这里直接不询问提交

 static const UPGRADE_COMMIT_REQ = 0x0F;void askForConfirmation(int type) {int code = -1;switch (type) {case ConfirmationType.COMMIT:{code = OpCodes.UPGRADE_COMMIT_CFM;}break;case ConfirmationType.IN_PROGRESS:{code = OpCodes.UPGRADE_IN_PROGRESS_RES;}break;case ConfirmationType.TRANSFER_COMPLETE:{code = OpCodes.UPGRADE_TRANSFER_COMPLETE_RES;}break;case ConfirmationType.BATTERY_LOW_ON_DEVICE:{sendSyncReq();}return;case ConfirmationType.WARNING_FILE_IS_DIFFERENT:{stopUpgrade();}return;}addLog("askForConfirmation ConfirmationType type $type $code");VMUPacket packet = VMUPacket.get(code, data: [0]);sendVMUPacket(packet, false);}

提交完成蓝牙会自动断开 ，间隔1S后重连 重新测试通知 再次发送升级请求跟文件md5 。如果数据正常 会收到是否安装的指令

 static const int COMMIT = 0x04

关于RWCP传输是基于以往0x1103中写入数据不等待返回通知，能大幅提高传输速率。

其他读者看代码理解吧

不懂得欢迎交流探讨
https://github.com/Liberations/Flutter-GAIAControl