====== Lab06 - 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.

===== Recieve by Interupt =====
  * In this session, we will receive data in an non-blocking manner using the interrupts
<code c> 
uint8_t Rx_char[1];

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) 
{
  HAL_UART_Receive_IT(&huart2, Rx_char, 1); 
}
int main(){
  HAL_UART_Receive_IT (&huart2, Rx_char, 1);

  while (1)
  {
  }
}
</code> 
  * The function ''HAL_UART_RxCpltCallback'' is called every time that board receives a data from UART. The execution of this function does not stop while loop from going on.


===== The NUCLEO stack =====

  * The NUCLEO side is expected to wait for the characters and add each received character to a stack. 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) 
 {
         if (Rx_char[0] != prev_Rx_char[0]){
                 prev_Rx_char[0] = Rx_char[0];
                 oRecvBuff.chArrRecvBuff[oRecvBuff.iCnt] = (char) Rx_char[0];
                 oRecvBuff.iCnt++;
                 HAL_UART_Transmit(&huart2, oRecvBuff.chArrRecvBuff , sizeof(oRecvBuff.chArrRecvBuff) ,10);
                 HAL_UART_Transmit(&huart2, enter  , sizeof(enter),10);
         }
 }
</code>
  * To see the complete project, download the files in link {{ :courses:be5b99cpl:labs:lab06_.zip |}}.

===== Exercise =====
  * 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 "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.