/******* CheckSum.c ************
 *
 * Use the same Fosc = 8 MHz as QwikBug uses.
 * A checksum for the contents of addresses 0x1A00-0x1FFF
 * will be sent to the PC.  This will allow a check on what revision
 * of the QwikBug kernal resides in the chip.
 * The checksum for the 20071029QB kernal is C198.
 *
 ******* Program hierarchy *****
 *
 * main
 *    Initial
 *    InitTX
 *    Check
 *
 *******************************
 */

#include <p18f4321.h>           // Define PIC18LF4321 registers and bits

/*******************************
 * Global variables
 *******************************
 */
unsigned char i;                // Index into string
unsigned char HEX;              // One hex character (0-15)
unsigned char ASCII;            // One ASCII-coded character
const char rom *RomPtr;         // Pointer to one-byte ROM elements
unsigned int CHECKSUM;          // Sixteen-bit checksum

/*******************************
 * Table in program memory
 *******************************
 */
 const char rom FormHex[] = "0123456789ABCDEF";

/*******************************
 * Function prototypes
 *******************************
 */
void Initial(void);
void Check(void);

/*******************************
 * Macro
 *******************************
 */
#define TXascii(in)  TXREG = in; while(!TXSTAbits.TRMT)

/////// Main program ////////////////////////////////////////////////////

void main()
{
   Initial();                   // Initialize everything
   Check();                     // Form checksum and send to PC
   Sleep();                     // Sleep forever
   Nop();
}

/*******************************
 * Initial
 *
 * This function performs all initializations of variables and registers.
 *******************************
 */
void Initial()
{
   OSCCON = 0b01110010;         // Use Fosc = 8 MHz (Fcpu = 2 MHz)
   RCSTA = 0b10010000;          // Enable UART
   TXSTA = 0b00100000;          // Enable TX
   SPBRG = 25;                  // Set baud rate
   BAUDCON = 0b00111000;        // Invert TX output
}

/*******************************
 * Check
 *
 * This function forms a checksum on QwikBug residing in program
 * memory from 0x1A00 to 0x1FFF.  It sends the checksum to the PC as
 * a hex number for display.
 *                          Prepared by Jeff Pitcher and Adam McDaniel
 *******************************
 */
void Check()
{
   CHECKSUM = 0;
   RomPtr = (const char rom *) (0x1A00);
   while (RomPtr <= (const char rom *)(0x1FFF))
   {
      CHECKSUM += *RomPtr++;    // Add into checksum
   }
   TXascii('\r');               // Send carriage return
   TXascii('\n');               //  and line feed
   HEX = (CHECKSUM & 0xF000) >> 12;  // Get upper nibble
   ASCII = FormHex[HEX];        // Convert to ASCII
   TXascii(ASCII);              //  and send to console
   HEX = (CHECKSUM & 0x0F00) >> 8;  // Get next nibble
   ASCII = FormHex[HEX];
   TXascii(ASCII);
   HEX = (CHECKSUM & 0x00F0) >> 4;  // Get third nibble
   ASCII = FormHex[HEX];
   TXascii(ASCII);
   HEX = (CHECKSUM & 0x000F);   // Get fourth nibble
   ASCII = FormHex[HEX];
   TXascii(ASCII);
}