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Lab07 - Nucleo Communication stack

The communication between Nucleo board and PC uses RS232 data link. The C language allows you to use multiple levels of abstraction as it is described in the following figure. The operating system (OS) level uses open, write, read, close function and the C standard library uses fopen, fwrite, fread and fclose functions. While the C standard library provides the same behavior on the all platforms the OS level can vary with implementation.

The NUCLEO side uses direct access to the CPU registers with functions USART_ReceiveData and USART_SendData. These functions have two parameters: the first is a pointer to the memory location with USART peripheral and the second is the character to be sent and received.

The NUCLEO stack

The NUCLEO side is expected to wait for the characters in a pooling mode which will be implemented as:

void main( void )
{
  init();

  while(1)
  {
    getCharacter();
    insertCharacterIntoBuffer();
  }
}

The reception management of the characters requires a data structure which is implemented as:

#define cRECV_BUFF_MAX 10
typedef struct tRecvBuff
{
  char chArrRecvBuff[cRECV_BUFF_MAX];
  int iCnt;
} tRecvBuff;
 
tRecvBuff oRecvBuff;

The structure is initialized as:

  oRecvBuff.chArrRecvBuff[0] = 0;
  oRecvBuff.iCnt = 0;  

And the reception is performed through:

  while(1) // Don't want to exit
  {
    uint16_t Data;
 
    while(USART_GetFlagStatus(USART2, USART_FLAG_RXNE) == RESET); // Wait for Char
 
    Data = USART_ReceiveData(USART2); // Collect Char
 
    oRecvBuff.chArrRecvBuff[ oRecvBuff.iCnt ] = (char)Data;
    oRecvBuff.iCnt++;  
 
    -- check the overflow of the array !! cRECV_BUFF_MAX
    -- wait for the end of the command !! propose a proper ending of the command, e.g. '\r' and '\n'
 
  } // END while(1)  

Exercise

  • Define and initialize necessary data structures to hold string commands sent over RS232 (such as “*IDN?\r\n”).
  • Define the mechanism of a “complete” command detection (based on '\r' and '\n').
  • Define the mechanism of buffer clearing after successful processing of the received command.
  • Detect the “*IDN?” command and reply with a description of your “device”.
  • Detect the “LED ON” and “LED OFF” commands to be able to control the User LED of the Nucleo board.
  • Detect the “BUTTON?” command to be able to read the User Button state.
courses/be5b99cpl/labs/lab07.txt · Last modified: 2018/10/04 15:47 (external edit)