/**** A P P L I C A T I O N   N O T E   A V R 3 2 5 ************************
 *
 * Title:          High-speed Interface to Host EPP Parallel Port
 * Version:        1.0
 * Last updated:   2001.12.20
 * Target:         All AVR Devices with 12 I/O pins or more
 *
 * Support E-mail: avr@atmel.com
 * 
 * DESCRIPTION
 * This Application Note describes a method for high-speed bidirectional data
 * transfer between an AVR microcontroller and an off-the-shelf Intel x86
 * desktop computer.
 *
 * This host program is constructed to talk to an AVR running AVREPP (over 
 * an EPP link).
 *
 * It functions more or less as a terminal program, passing keyboard data 
 * into the AVR, and displaying data from the AVR on the screen. The program 
 * exits if ESC (0x1b) is typed.
 *
 * This program expects the EPP to be at LPT1 (0x378); to change this, change 
 * PPORT below. 
 *
 * This program was written for DOS Turbo-C 2.01
 ***************************************************************************/

#include <dos.h>                /* inp, outp                               */
#include <conio.h>              /* kbhit() et al                           */

#define PPORT   0x378           /* LPT1                                    */

#define EPPSTAT(_p) ((_p)+1)    /* EPP/SPP status register                 */
#define EPPDATA(_p) ((_p)+4)    /* EPP data register                       */
#define SPPCTL(_p)  ((_p)+2)    /* SPP Control Register                    */

/*
 *      status register bits
 */
#define	EPPTIMEOUT 0x01
#define EPPBSY     0x80
#define	EPPINTR	   0x40
#define EPPINIT    0x04         /* 0bxxxx0100                             */

#define ESC        0x1B         /* use this to quit                       */

int main(int argc, char *argv[])
{

    unsigned char c, r;

    if (argc || argv)           /* ARGSUSED                               */
        ;

    outp(SPPCTL(PPORT), EPPINIT);      /* FAMcK                           */

    /* Forever (or at least until user types Esc):                        */

    while (1) 
    {

        /* Check keyboard side                                            */

        if (kbhit()) 
        {
            /* Something typed -- pass it through                         */

            c = getch();           /* get what user typed                 */
            if (c == ESC)          /* way-out                             */
	        break;
            outp(EPPDATA(PPORT), c);	/* write to port */
        }

        /* Check EPP (Rx) side. The EPP peripheral (the AVR) indicates    */
        /* that data is ready via the INTR signal.                        */

        r = inp(EPPSTAT(PPORT));

        if ((r & EPPBSY) == 0)      /* powered down?                      */
            continue;               /* ignore it                          */

        if (r & EPPINTR)            /* intr is request to read            */ 
        {		
            c = inp(EPPDATA(PPORT));	/* so do it		          */
            r = inp(EPPSTAT(PPORT));	/* get the status register        */

            /* If we're following the protocol (reading only on EPPINTR)  */
            /* we should Never see a timeout.                             */

            if (r & EPPTIMEOUT) 
            {
                outp(EPPSTAT(PPORT), EPPTIMEOUT); /* clear it             */
                c = '@';                        /* display '@' on timeout */
            }
            putch(c);                           /* display on the screen  */
        }
    } /* end while(1)                                                     */

    return(0);
}