B站：https://space.bilibili.com/309103931

中移4G模块-ML302专栏：https://blog.csdn.net/qq_33259323/category_10453372.html

中移4G模块-ML302文集：https://www.bilibili.com/read/readlist/rl328642

1.中移4G模块-ML302-OpenCpu开发-(固件编译和烧录)

https://blog.csdn.net/qq_33259323/article/details/108586847

https://www.bilibili.com/read/cv7876504

2.中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云)

https://blog.csdn.net/qq_33259323/article/details/108638945

https://www.bilibili.com/read/cv7876527

2.1中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-订阅主题)

https://blog.csdn.net/qq_33259323/article/details/108960540

https://www.bilibili.com/read/cv7879954

2.2中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-接收和发送数据)

https://blog.csdn.net/qq_33259323/article/details/108964810

https://www.bilibili.com/read/cv7886836

2.3中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-RRPC通讯)

https://blog.csdn.net/qq_33259323/article/details/108965071

https://www.bilibili.com/read/cv7888259

3.中移4G模块-ML302-OpenCpu开发-串口开发

https://blog.csdn.net/qq_33259323/article/details/108974888

https://www.bilibili.com/read/cv7888865

4.中移4G模块-ML302-OpenCpu开发-51单片机串口转I2C

https://blog.csdn.net/qq_33259323/article/details/109020642

https://www.bilibili.com/read/cv7922942

5.中移4G模块-ML302-OpenCpu开发-MCP23017输入/输出

https://blog.csdn.net/qq_33259323/article/details/109109136

https://www.bilibili.com/read/cv7969395

7.中移4G模块-ML302-OpenCpu开发-PCF8591测量电压

https://blog.csdn.net/qq_33259323/article/details/109109266

https://www.bilibili.com/read/cv7969365

8.中移4G模块-ML302-OpenCpu开发-GPIO

https://blog.csdn.net/qq_33259323/article/details/108960947

https://www.bilibili.com/read/cv7877192

9.中移4G模块-ML302-OpenCpu开发-ADC

https://blog.csdn.net/qq_33259323/article/details/109020864

https://www.bilibili.com/read/cv7922958

10.中移4G模块-ML302-OpenCpu开发-CJSON

https://blog.csdn.net/qq_33259323/article/details/109020898

https://www.bilibili.com/read/cv7923020

11.中移4G模块-ML302-OpenCpu开发-HTTP

https://blog.csdn.net/qq_33259323/article/details/109020904

https://www.bilibili.com/read/cv7923054

中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-RRPC通讯)

什么是RRPC通信

MQTT协议是基于PUB/SUB的异步通信模式，不适用于服务端同步控制设备端返回结果的场景。物联网平台基于MQTT协议制定了一套请求和响应的同步机制，无需改动MQTT协议即可实现同步通信。物联网平台提供API给服务端，设备端只需要按照固定的格式回复PUB消息，服务端使用API，即可同步获取设备端的响应结果。

名词解释

RRPC：Revert-RPC。RPC（Remote Procedure Call）采用客户机/服务器模式，用户不需要了解底层技术协议，即可远程请求服务。RRPC则可以实现由服务端请求设备端并能够使设备端响应的功能。RRPC 请求消息：云端下发给设备端的消息。RRPC 响应消息：设备端回复给云端的消息。RRPC 消息ID：云端为每次RRPC调用生成的唯一消息ID。RRPC 订阅Topic：设备端订阅RRPC消息时传递的Topic，含有通配符。

RRPC原理

具体流程如下：

物联网平台收到来自用户服务器的RRPC调用，下发一条RRPC请求消息给设备。消息体为用户传入的数据，Topic为物联网平台定义的Topic，其中含有唯一的RRPC消息ID。设备收到下行消息后，按照指定Topic格式（包含之前云端下发的唯一的RRPC消息ID）回复一条RRPC响应消息给云端，云端提取出Topic中的消息ID，和之前的RRPC请求消息匹配上，然后回复给用户服务器。如果调用时设备不在线，云端会给用户服务器返回设备离线的错误；如果设备没有在超时时间内（8秒内）回复RRPC响应消息，云端会给用户服务器返回超时错误。

RRPC通信相关Topic

RRPC通信相关Topic格式如下：

RRPC请求消息Topic：/sys/${YourProductKey}/${YourDeviceName}/rrpc/request/${messageId}RRPC响应消息Topic：/sys/${YourProductKey}/${YourDeviceName}/rrpc/response/${messageId}RRPC订阅Topic：/sys/${YourProductKey}/${YourDeviceName}/rrpc/request/+

以上内容来自https://help.aliyun.com/document_detail/90567.html

由上面可以看出需要在topic中获得messageId，然后在发送回去

 

如果你的ML302模块还没有连上阿里云可以看一下这个，中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云)

https://blog.csdn.net/qq_33259323/article/details/108638945

https://www.bilibili.com/read/cv7876527

1.订阅RRPC example_subscribe_rrpc函数

int example_subscribe_rrpc(void *handle){ int res = 0; const char *fmt = "/sys/%s/%s/rrpc/request/+"; char *topic = NULL; int topic_len = 0; topic_len = strlen(fmt) + strlen(DEMO_PRODUCT_KEY) + strlen(DEMO_DEVICE_NAME) + 1; topic = HAL_Malloc(topic_len); if (topic == NULL) { cm_printf("[ALIYUN]: memory not enough\n"); return -1; } memset(topic, 0, topic_len); HAL_Snprintf(topic, topic_len, fmt, DEMO_PRODUCT_KEY, DEMO_DEVICE_NAME); cm_printf("topic:%s \r\n",topic); res = IOT_MQTT_Subscribe(handle, topic, IOTX_MQTT_QOS0, example_message_arrive_rrpc, NULL); if (res < 0) { cm_printf("[ALIYUN]: subscribe failed\n"); HAL_Free(topic); return -1; } HAL_Free(topic); return 0; }

  2.接收数据 example_message_arrive_rrpc函数

char DEMO_RRPC_SessionId[19]; void example_message_arrive_rrpc(void *pcontext, void *pclient, iotx_mqtt_event_msg_pt msg){ iotx_mqtt_topic_info_t *topic_info = (iotx_mqtt_topic_info_pt) msg->msg; char * sendMessage = NULL; const char * sendMessage_fmt = "%d"; int sendMessage_len = 20; int cm_test_read_gpio = 0; cm_printf("example_message_arrive_rrpc \n"); switch (msg->event_type) { case IOTX_MQTT_EVENT_PUBLISH_RECEIVED: /* print topic name and topic message */ cm_printf("[ALIYUN]: Message Arrived:"); cm_printf("Topic : %.*s", topic_info->topic_len, topic_info->ptopic); cm_printf("Payload: %.*s", topic_info->payload_len, topic_info->payload); cm_printf("\n"); // 提取sessionId strncpy(DEMO_RRPC_SessionId,topic_info->ptopic+46,19); cm_printf("[ALIYUN]: sessionId: %s",DEMO_RRPC_SessionId); //接收到的数据：topic_info->payload //干啥干啥干啥 // 发送 example_publish_rrpc(sendMessage); break; default: break; } }

3.发送数据 example_publish_rrpc函数

int example_publish_rrpc(unsigned char * payload) { int res = 0; const char *fmt = "/sys/%s/%s/rrpc/response/%s"; char *topic = NULL; int topic_len = 0; //char *payload = "{\"message\":\"hello!\"}";] cm_printf("MQTT发送信息：%s",payload); topic_len = strlen(fmt) + strlen(DEMO_PRODUCT_KEY) + strlen(DEMO_DEVICE_NAME) + 1 +strlen(DEMO_RRPC_SessionId); topic = HAL_Malloc(topic_len); if (topic == NULL) { cm_printf("[ALIYUN]: memory not enough\n"); return -1; } memset(topic, 0, topic_len); HAL_Snprintf(topic, topic_len, fmt, DEMO_PRODUCT_KEY, DEMO_DEVICE_NAME,DEMO_RRPC_SessionId); cm_printf("[ALIYUN]: example_publish_rrpc: %s",topic); res = IOT_MQTT_Publish_Simple(0, topic, IOTX_MQTT_QOS0, payload, strlen(payload)); if (res < 0) { cm_printf("[ALIYUN]: publish failed, res = %d\n", res); HAL_Free(topic); return -1; } HAL_Free(topic); return 0; }