/* p3_4.c: Matrix keypad detect
 *
 * This program checks a 4x4 matrix keypad to see whether
 * a key is pressed or not. When a key is pressed, it turns
 * on the blue LED.
 *
 * Port4 7-4 are connected to the columns and Port4 3-0 are connected
 * to the rows of the keypad.
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0.
 */

#include "msp.h"

void delay(void);
void keypad_init(void);
char keypad_kbhit(void);

int main(void) {
    keypad_init();
    P2->DIR = 0x04;                 /* make blue LED pins output */
    
    while(1) {
        if (keypad_kbhit() != 0)    /* if a key is pressed */
            P2->OUT |= 0x04;        /* turn on blue LED */
        else
            P2->OUT &= ~0x04;       /* turn off blue LED */
    }
}

/* this function initializes Port 4 that is connected to the keypad.
 * All pins are configured as GPIO input pin. The column pins have
 * the pull-up resistors enabled.
 */
void keypad_init(void) {
    P4->DIR = 0;
    P4->REN = 0xF0;     /* enable pull resistor for column pins */
    P4->OUT = 0xF0;     /* make column pins pull-ups */
}

/* This is a non-blocking function.
 * If a key is pressed, it returns 1.
 * Otherwise, it returns a 0 (not ASCII '0'). */

char keypad_kbhit(void) {
    int col;

    P4->DIR |= 0x0F;            /* make all row pins output */
    P4->OUT &= ~0x0F;           /* drive all row pins low */
    delay();                    /* wait for signals to settle */
    col = P4->IN & 0xF0;        /* read all column pins */
    P4->DIR &= ~0x0F;           /* disable all row pins drive */
    if (col == 0xF0)            /* if all columns are high */
        return 0;               /* no key pressed */
    else
        return 1;               /* a key is pressed */
}

/* make a small delay */
void delay(void) {
}