====== 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. 

{{ :courses:be5b99cpl:labs:rs232.png?direct |}}

===== The NUCLEO stack =====
The NUCLEO side is expected to wait for the characters in a pooling mode which will be implemented as:
<code>
void main( void )
{
  init();

  while(1)
  {
    getCharacter();
    insertCharacterIntoBuffer();
  }
}
</code>

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

<code c>
#define cRECV_BUFF_MAX 10
typedef struct tRecvBuff
{
  char chArrRecvBuff[cRECV_BUFF_MAX];
  int iCnt;
} tRecvBuff;

tRecvBuff oRecvBuff;
</code>

The structure is initialized as:

<code c>
  oRecvBuff.chArrRecvBuff[0] = 0;
  oRecvBuff.iCnt = 0;  
</code>

And the reception is performed through:

<code c>
 
  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)  
</code>

===== 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.