/***************************************************************************
 *                       LOOP BACK TEST PROGRAM                            *
 * This program uses the loop back feature of the 16450 chip to transmit   *
 * a sequence of characters and in turn receive them.  No external jumpers *
 * are required to run this program.                                       *
 ***************************************************************************/
#include <stdio.h>
#include <dos.h>


#define RECEIVE     0           /* Receiver buffer register              */
#define TRANSMIT    0           /* Transmitter holding register          */
#define L_DIVISOR   0           /* Divisor latch, least significant byte */
#define U_DIVISOR   1           /* Divisor latch, most significant byte  */
#define INT_ENB     1           /* Interrupt enable register             */
#define INT_ID      2           /* Interupt identification register      */
#define LINE_CTRL   3           /* Line control register                 */
#define MODEM_CTRL  4           /* Modem control register                */
#define LINE_STAT   5           /* Line status register                  */
#define MODEM_STAT  6           /* Modem status register                 */


unsigned AskForBaseAddress(unsigned int OldOne)
{
	char msg[7];
	int NewOne = 0, Success = 0, Dummy;
	int AddrInputPosX, AddrInputPosY;

	puts("\nPlease enter the Base Address for your card (in hex)");
	printf("or press ENTER for %X.\n>", OldOne);
	AddrInputPosX = wherex(); AddrInputPosY = wherey();
	do {
      gotoxy(AddrInputPosX, AddrInputPosY);
      clreol();
      msg[0] = 5; msg[1] = 0;
      cgets(msg);
      sscanf(msg + 2, "%x", &NewOne);
      Success = 1;
      Dummy = NewOne;
		if (msg[1] == 0) {
        gotoxy(AddrInputPosX, AddrInputPosY);
        printf("%X", OldOne);
        Success = 1;
        Dummy = OldOne;
      }
	} while(!Success);
	return (Dummy);
} /* end of AskForBaseAddress */

/**************************************************************************
 * PROCEDURE initialize - Performs the setup and initialization of the    *
 *                        16450 chip.                                     *
 **************************************************************************/

void initialize(Address)
{
/* First, set up the divisor latches for 9600 baud.  A divisor of 12 is
   required since the 1.8432 clock is used.  The upper divisor is set to
   0 and the lower to 12. */
outportb(Address + LINE_CTRL,0x80); /* Set DLAB high for Divisor latch enable */
outportb(Address + L_DIVISOR,12);   /* Load lower latch with 12 */
outportb(Address + U_DIVISOR,0);    /* Load upper latch with 0  */

/* Now set the line control register for the following communications
   protocol
		bit0, bit1 = 1 -- character is eight bits
		      bit2 = 0 -- one stop bit
		      bit3 = 0 -- no parity is enabled
		      bit4 = 0 -- doesn't matter with parity disabled
		      bit5 = 0 -- doesn't matter with parity disabled
		      bit6 = 0 -- disable break control
		      bit7 = 0 -- DLAB bit, 0 disables divisor latches    */
outportb(Address + LINE_CTRL,0x03);

/* Enable the loop back feature of the chip with bit 4 of modem control
   register, now all transmitted characters will be looped back to the
   receiver, without external connections. */
outportb(Address + MODEM_CTRL,0x10);

/* these inputs are to just insure that both the receiver buffer register
   and receiver shift register are clear. */

delay(50);
inportb(Address + RECEIVE);   /* clear rx registers */
delay(50);
inportb(Address + RECEIVE);
}

/***************************************************************************
 * PROCEDURE main - transmit the letters 'A' through 'Z', and in turn,     *
 *                  receive the characters, and check if the correct char  *
 *                  is received.  The program will print an error message  *
 *                  for each bad character received. If no errors occur,   *
 *                  the program will indicate so at the end of program     *
 *                  execution.                                             *
 *                                                                         *
 ***************************************************************************/
void main()
{
unsigned int Address;
unsigned char ch,ch1,flag;

clrscr();
printf("                 Sample One   :   Internal loopback test.\n\n");
puts("This program uses the loop back feature of the 16450 chip to transmit ");
puts("a sequence of characters and in turn receive them.  No external jumpers");
puts("are required to run this program.\n ");
   clrscr();
   printf("\n\n\nBoard Configuration:\n\n");
   printf(" -- Base Address is %x hex\n",Address);
   puts(" -- All remaining jumper settings are irrelevant\n\n\n\n");
   printf("\nPress any key to continue, or E to exit.\n");
   if(toupper(getch())=='E') return;

   delay(0);                   /* initialize the Borland delay function */
   initialize(Address);               /* setup the 16450 chip */

   flag = 0;
   for (ch = 'A';ch <= 'Z';ch++)
      {
      outportb(Address + TRANSMIT,ch);
      do
         {
         ch1 = inportb(Address + LINE_STAT);   /* send the char */
         }
      while ((ch1 & 1) == 0);  /* check if bit 1 is a 1, if so, data is ready */
      ch1 = inportb(Address + RECEIVE);   /* read the input char */

      /* check if char received is the one we sent */
      if (ch1 != ch)
         {
         printf("error with character %c, received char %c.\n",ch,ch1);
         flag = 1;
         }
      }
   if (flag == 0)  /* then no errors occured */
      {
      clrscr();
      printf("\n\n\nAll characters were transmitted without error. ");
      }
}