Raspberry Pi and Echo LED

//***************************************************************************************

#include <stdio.h>        
#include <delays.h>
#include "USARTfunc.h" // header for configureUSART(baud) , set_osc_32MHz()
                            //   and WaitOneSecond()

void main(void)  
{
    unsigned char Rx=0;

    set_osc_8MHz(); // set MCU to run at 8 MHz
    configureUSART(115200ul, 8);

    [printf](http://www.opengroup.org/onlinepubs/009695399/functions/printf.html)("\tpic18lf2620\r\nAugust 12, 2012\r\nby Dan Peirce B.Sc.\r\nEcho to sender....\r\n");

    test_overrun();

    while(1)
    {

       Rx = echoRx();      // function sends Rx value to Tx (unless null)

       test_overrun();         
    }

}

void configureUSART(unsigned long baudrate, unsigned char osc_freq_MHz);

void set_osc_8MHz(void);

void WaitOneSecond(void);

void test_overrun(void);
unsigned char echoRx(void);

// These are not C statements but directives to the C18 compiler. They result in configuration
// bits in the PIC18F4525 being set in the flash memory. This configuration is set when the 
// PIC is programmed by the PICkit2 programmer and before any program starts to run in the PIC.

#pragma config WDT = OFF
#pragma config OSC = INTIO7      // puts osc/4 on pin 10 (0n 28 pin package) to check freq
#pragma config MCLRE = OFF
#pragma config LVP = OFF
#pragma config PBADEN = OFF      // PORTB<4:0> are digital IO

//****************************************************************************************
#include <stdio.h>
#include <p18f2620.h>
#include <usart.h>       // library containing serial communtication functions
#include <delays.h>      // library containing delays - i.e. wait for time t

void resetRxEnable(void);

void configureUSART(unsigned long baudrate, unsigned char osc_freq_MHz)
{
  unsigned int spbrg;

  TRISCbits.TRISC6 = 0;     // set TX (RC6) as output 
  TRISCbits.TRISC7 = 1;     // and RX (RC7) as input

  // For a 16-bit sbprg value with USART_BRIGH_HIGH setting.
  // Formula from datasheet is Baudrate = FOSC/ (4 * (spbrg + 1 ))
  spbrg = (unsigned int)( ((float)osc_freq_MHz * 1.0e6) /(4.0*(float)baudrate) + 0.5 - 1.0);

  OpenUSART( USART_TX_INT_OFF & USART_RX_INT_OFF & USART_ASYNCH_MODE & USART_EIGHT_BIT & 
             USART_CONT_RX & USART_BRGH_HIGH, spbrg );  
  // OpenUSART is part of the C18 usart.h library

  BAUDCONbits.BRG16 = 1;  // needed so we can use a 16-bit spbrg
        // Note that this is not discussed in the c18 Compiler Libraries guide
  Delay10KTCYx(1); // small 4x0.0125 s delay to allow communication speed to stabilize
                    // part of the C18 delays.h library
}              // original delay was 0.0125 s but that was with Fosc at 32 MHz (now is 8MHz)

void test_overrun(void)
{
  if(RCSTAbits.OERR == 1u) resetRxEnable(); //check for overrunn error; reset if needed
}

void resetRxEnable(void)    
{ 
    [printf](http://www.opengroup.org/onlinepubs/009695399/functions/printf.html)("\r\n***caught Rx overrun!***\r\n");                         
    RCSTAbits.CREN = 0;
    RCSTAbits.CREN = 1;
}

unsigned char echoRx(void)
{
    unsigned char rx=0;

    if(DataRdyUSART())  
    {
        rx = ReadUSART();
        WriteUSART(rx);
    }
    return rx;
}

//***********************************************************************************
//                          set_osc_8MHz()
//    sets the oscillator from the default 1 MHz to 8 MHz
//***********************************************************************************

void set_osc_8MHz(void)
{
  int i;

  OSCCONbits.IRCF2 = 1;     // Set the OSCILLATOR Control Register to 8 MHz
  OSCCONbits.IRCF1 = 1;      
  OSCCONbits.IRCF0 = 1;        
}

void WaitOneSecond(void)
{
    Delay10KTCYx(200); // wait 10 000 * 200 * TCY = 1.000 seconds

}