MCU SDK Porting

The MCU SDK contains all you need to get started with MCU development, such as functions and sample code. It is automatically generated based on the product features defined on the Tuya Developer Platform. This topic describes how to port the NB-IoT MCU SDK to your project.

Overview

The MCU SDK is automatically generated based on the product features defined on the Tuya Developer Platform. To facilitate your integration with Tuya’s NB-IoT general serial protocol, the MCU SDK has built-in support for communication and protocol parsing. You can add this SDK to existing projects and complete the required configuration to implement the MCU program development.

Resource requirements

The SDK requirements for the MCU are as follows. If your hardware is constrained in resources, you can refer to functions in the SDK and port the protocol yourself.

• Memory: 4 KB
• RAM: About 100 bytes of RAM are required, depending on the data length of the data point (DP). If you enable OTA updates, it must be greater than 260 bytes.
• Nested function: 9-level.

File structure

How to port SDK

1. Program the MCU and port the SDK.
2. Configure the operation mode and cloud connectivity for the product based on nbiot.h.
3. Check macro definitions in protocol.h.
4. Port the protocol.c file and functions.
5. Add the function for DP data communication.

Step 1: Programming and porting

1. In your original project, initialize the MCU peripherals, including the serial port and GPIO (configure the NB-IoT wakeup source).

2. Copy the .c and .h files in the MCU SDK folder to your project directory where the .c and .h files are located.

   

Step 2: Check the parameter configurations in nbiot.h.

1. Define the operation mode: SIM_MODE specifies the operation mode that can be set to psm, drx, or edrx. The operation mode you set must be the same as that of the product you create on the Tuya Developer Platform.
2. Define cloud connectivity: CONNECT_MODE specifies how the NB-IoT module is connected to the Tuya cloud. Valid values include isp and tuya. The mode you set must be the same as that of the product you create on the Tuya Developer Platform.
   • isp: The NB-IoT module is connected to the carrier’s cloud and then to the Tuya cloud.
   • tuya: The NB-IoT module is directly connected to the Tuya cloud. Currently, this mode applies to China Mobil SIM cards only.
3. Configure MCU updates: SUPPORT_MCU_FIRM_UPDATE specifies whether to enable MCU updates or file downloads. You can enable this macro if you need this feature.

Step 3: Check macro definitions in protocol.h

1. Define product ID (PID): PRODUCT_KEY is the macro defined for the PID. PID is the unique identifier of each product. It can be found on the page of Product Development.

   If the PRODUCT_KEY and the PID are inconsistent, you can go to Hardware Development > Download Documents section and download the latest SDK.

   #define PRODUCT_KEY  "ny18le8hpsb3z97g"
   

2. Define MCU version number: MCU_VER specifies the software version, which defaults to 1.0.0. If you enable OTA updates for the MCU firmware, you need to update the MCU version number after the firmware update is installed.

   #define MCU_VER "1.0.0"
   

3. Configure clock synchronization: SUPPORT_MCU_RTC_CHECK specifies whether to enable clock synchronization with a time server. If your product is time-sensitive, this feature can ensure the RTC of the NB-IoT module is accurate. If you enable this macro, you need to implement mcu_write_rtctime in protocol.c.

(Optional) Step 4: Transmit and receive buffer

• Serial receive buffer: The buffer size depends on how often the serial data handler is called. If the MCU can quickly process serial data, the buffer size can be reduced.

• Serial transmit buffer: The buffer size must be greater than the maximum length of DP data.

• Buffer for serial data processing: The buffer size must be greater than the maximum length of DP data. If the OTA update feature is enabled, adjust the buffer size accordingly.

  /******************************************************************************
                          3: Define the transmit and receive buffer:
                       If your MCU has insufficient RAM, you can change the buffer size to 24 bytes.
  ******************************************************************************/
  #ifndef SUPPORT_MCU_FIRM_UPDATE
  #define NBIOT_UART_QUEUE_LMT             16              //The size of the data receive queue, which can be reduced if your MCU has insufficient RAM.
  #define NBIOT_UART_RECV_BUF_LMT          24              //It depends on the amount of DP data but must be greater than 24 bytes.
  #else
  #define NBIOT_UART_QUEUE_LMT             128              //The size of the data receive queue, which can be reduced if your MCU has insufficient RAM.
  #define NBIOT_UART_RECV_BUF_LMT          300              //It depends on the amount of DP data but must be greater than 24 bytes.
  #endif
  #define NBIOT_UART_SEND_BUF_LMT          64               //It depends on the amount of DP data but must be greater than 24 bytes.
  /******************************************************************************
  

Step 5: Port protocol.c file and functions

1. Copy the nbiot.h file to the folder where NB-IoT files are stored, such as the main.c folder.

2. Call the nbiot_protocol_init() function in the mcu_api.c file after the MCU serial port and other peripherals are initialized.

3. Specify the serial transmission function in uart_transmit_output in the protocol.c file, and delete #error.

   Example:

   void uart_transmit_output(unsigned char value)
   {
     extern void Uart_PutChar(unsigned char value);
     Uart_PutChar(value);                                    // Serial transmission function
   }
   

4. In the interrupt handler for serial data reception, call uart_receive_input in the mcu_api.c file and pass in the received data as the parameters.

   Example:

   void USART3_IRQHandler(void)
   {
       unsigned char Res=0;
   
       if((USART3->SR&UART_FLAG_RXNE) != 0)
       {
           Res=USART3->DR;
           uart_receive_input(Res);
       }
   }
   

5. After the MCU runs in the while(1) loop, it calls the cellular_uart_service() function in the mcu_api.c file. The sample code in main.c is as follows:

   #include "nbiot.h"
   ...
   void main(void)
   {
       nbiot_protocol_init();
       ...
       while(1)
       {
           nbiot_uart_service();
           ...
       }
       ...
   }
   

   The MCU must directly call the nbiot_uart_service() function in the mcu_api.c file in the while(1) loop. After the program is initialized, if an interrupt service routine (ISR) is necessary, you must keep it as short as possible. Do not call the data reporting function to avoid loss of data.

Things to note

Power saving lock

The NB-IoT module sleeps when it is idle (no data communication) to save power.

If the MCU needs to process a large amount of data and does not want the NB-IoT module to sleep, it can send the power saving lock command to the NB-IoT module to prevent it from sleeping. After data processing is finished, the MCU can send the power saving lock command to the NB-IoT module again to resume the sleep pattern.

Discrete approach

NB-IoT features multi-connection and low power and cost. However, the narrowband imposes a limit on the number of concurrent connections.

• When you onboard a large number of devices at the same time, you can use the discrete approach to process concurrent requests from NB-IoT devices to achieve overload control.

• You need to test how the discrete approach works on the MCU side to ensure the effect is as expected.

• The discrete approach only works for power on startup. The discrete approach to data reporting should be maintained separately on the MCU side. If the NB-IoT module on your product is designed to be powered off and on frequently, do not use the discrete approach.

/*****************************************************************************
Function name: mcu_set_discrete_info
Function description: Set the discrete approach to the first power-on startup for the NB-IoT module.
Input parameter: en: 0 means to disable the discrete approach. 1 means to enable the discrete approach.
          duration: The maximum duration of random discrete, ranging from 120 to 1,800. For example, if `duration` is set to 150, the random range is 0 to 150.
          step: The step of the discrete range. With the same duration, a smaller step leads to larger discrete.

Return parameter: none
Description: 
*****************************************************************************/
void mcu_set_discrete_info(unsigned char en, unsigned int duration, DISCRETE_STEP step)
{
    unsigned int  du = 0;
    unsigned int  length = 0;
    unsigned char uart_buff[128] = {0};

    du = duration;
    if (duration < 120){
        du = 120;
    }
    if (duration > 1800){
        du = 1800;
    }

    length = snprintf(uart_buff, sizeof(uart_buff), "{\"enable\":%d,\"duration\":%d,\"step\":%d}",\
                                                   (unsigned int)en, du, (unsigned int)step);

    length = set_nbiot_uart_buffer(0, uart_buff, length);
    nbiot_uart_write_frame(SET_DISCRETE_INFO_CMD, length);
}

Call DP data communication function

For more information, see MCU SDK Porting for Wi-Fi Protocol.

OTA updates or file download

This section describes how the MCU and the NB-IoT module communicate during OTA updates or file downloads.

Perform a cyclic redundancy check (CRC) on firmware when an update is initiated to avoid downloading duplicate data.

case MCU_OTA_START_CMD:
...
// Return a response to the module.
    #error "Implement the response to the packet size for transmission and the offset address, and then delete this line"
    /*
      1. Calculate the CRC value (crc32_app) of the firmware that is running.
      2. Compare the calculated value with the firm_crc32 given at the beginning of the update.
      if (firm_crc32 == crc32_app) {
        // If the firmware already exists, download is not needed. The MCU only needs to return the file length.
        mcu_firm_update_start_ack(unsigned char unit_len, firm_length);
      }
      else {
        //The MCU returns the offset address for resumable transfer or returns 0 for download from the beginning.
        mcu_firm_update_start_ack(unsigned char unit_len, unsigned long received_len);
      }
    */
...
break;

If the update installation is repeated, compare the firmware CRC to detect duplicate data.

/*****************************************************************************
Function name: mcu_firm_update_handle
Function description: The MCU enters update mode.
Input parameter: value indicates the firmware buffer.
          position: Indicates where the packet is located in the firmware.
          length: The length of the current update package. When the length is zero, the transmission is completed.
Return parameter: none
Description: This function is intended to be implemented by you.
*****************************************************************************/
unsigned char mcu_firm_update_handle(const unsigned char value[],unsigned long position,unsigned short length)
{
  #error "Complete the implementation for OTA MCU update and then delete this line."
  if(length == 0)
  {
    // Transmission of updates is completed.

    #error "Follow the steps below to perform CRC32 checks and return the result of 0 or 1. Delete this line after you implement the code."
    /*
      1.Calculate the CRC value (crc32_app) of the downloaded firmware.
      2.Calculate the CRC value (crc32_app) of the firmware that is running.
      3.Compare the calculated value with the CRC32 value given at the beginning of the update.
      if (crc32 == crc32_dl) {        //The firmware is downloaded. Navigating to the latest firmware.
        mcu_firm_update_data_ack(1, 0);        //CRC check passed.
        //Navigate to the required application.
      }
      else if (crc32 == crc32_app){        //The latest firmware is running. The MCU returns a response.
        mcu_firm_update_data_ack(1, 0);        //CRC check passed.
      }
      else {
        mcu_firm_update_data_ack(1, 1);        //CRC check failed.
      }
    */

  }
  else
  {
    //mcu_firm_update_data_ack(0, 0);

    // Process the firmware.

  }

  return SUCCESS;
}