/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\
 * JOYSTICK.C -- by Gary Neal, Jr.                                       *
 *                                                                       *
 * Source code for our functions that access the joystick controls.      *
\* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

#include "joystick.h"

/* Joystick potentiometer values */
unsigned short joyPotVal[4];

/* Flags if using BIOS or direct access for joystick interface */
char joystickDirectAccess = 0;

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\
 * Joyin                                                                 *
 *                                                                       *
 * Samples all four joystick pots and stores their values in             *
 * joyPotVal[0] through joyPotVal[3].                                    *
 *                                                                       *
 * For Joystick's X-axis, the minimum value is LEFT.                     *
 * For Joystick's Y-axis, the minimum value is UP.                       *
\* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
void Joyin(int joyTest)
{
    union REGS regs;         /* Declare register variable, BIOS call */
    unsigned int limit;      /* Limit for direct access timing */
    unsigned char joyState;  /* Current state for direct access */
    static char joyMask;     /* Joystick direct access mask enabler */

    if (joystickDirectAccess) {

        /* Clear the joystick potentiometer values */
        joyPotVal[0] = joyPotVal[1] = joyPotVal[2] = joyPotVal[3] = limit = 0;

        /* Enable all joystick pots if in test mode */
        if (joyTest) joyMask = 0x0F;

        disable();           /* Disable interrupts for direct access */
        outp(0x201, 0);      /* Discharge joystick caps */

        /* While limit > 0 and joystick caps not fully charged */
        while (joyState = (inp(0x201) & joyMask)) {

            /* Test and increment joystick pot values */
            joyPotVal[JsA_Xaxis] += joyState & 1;
            joyState >>= 1;
            joyPotVal[JsA_Yaxis] += joyState & 1;
            joyState >>= 1;
            joyPotVal[JsB_Xaxis] += joyState & 1;
            joyState >>= 1;
            joyPotVal[JsB_Yaxis] += joyState & 1;

            /* Count the loop limit, break if limit reached */
            if (!(++limit)) break;
        }
        enable();            /* Re-enable interrupts */

        if (joyTest) {
            /* Mask off caps with no corresponding pot values */
            joyMask = (joyPotVal[JsA_Xaxis] != 0) << JsA_Xaxis |   /* Bit 0 */
                      (joyPotVal[JsA_Yaxis] != 0) << JsA_Yaxis |   /* Bit 1 */
                      (joyPotVal[JsB_Xaxis] != 0) << JsB_Xaxis |   /* Bit 2 */
                      (joyPotVal[JsB_Yaxis] != 0) << JsB_Yaxis;    /* Bit 3 */
        }

    } else {

        regs.h.ah = 0x84;    /* Joystick BIOS functions */
        regs.x.dx = 0x01;    /* Get joystick pot values */

        /* Call BIOS to get the pot values */
        int86(0x15, &regs, &regs);

        /* Store the registers returned as our pot values */
        joyPotVal[JsA_Xaxis] = regs.x.ax;
        joyPotVal[JsA_Yaxis] = regs.x.bx;
        joyPotVal[JsB_Xaxis] = regs.x.cx;
        joyPotVal[JsB_Yaxis] = regs.x.dx;

    }
}

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\
 * JoystickButtonPressed                                                 *
 *                                                                       *
 * Samples the joystick buttons state and returns the desired bits       *
 * determined by the bit mask (buttonMask).                              *
 *                                                                       *
 * If you want to return the bits for all buttons, pass (JsAllButtons)   *
 * to this function.                                                     *
 *                                                                       *
 * The state of the desired bits is 1 if button is pressed, 0 if not.    *
\* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
int JoystickButtonPressed(int buttonMask)
{
    union REGS regs;    /* Declare register variable for BIOS call */

    if (joystickDirectAccess) {

        /* Return the buttons state */
        return ((~inp(0x201)) & buttonMask);

    } else {
        regs.h.ah = 0x84;  /* Joystick BIOS functions */
        regs.x.dx = 0x00;  /* Read joystick buttons state */

        /* Call BIOS to get the buttons state */
        int86(0x15, &regs, &regs);

        /* Return the buttons state */
        return ((~regs.h.al) & buttonMask);
    }
}