/* 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 yellow LED0.
 *
 * PortB 07-04 are connected to the columns and PortB 3-0 are connected
 * to the rows of the keypad. The columns are used for inputs while
 * the rows are used for excitation outputs.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a
 */

#include "samd21.h"

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

int main(void) {
    keypad_init();
    REG_PORT_DIRSET1 = 0x40000000;          /* make PB30 output for LED0 */

    while(1) {
        if (keypad_kbhit() != 0)            /* if a key is pressed */
            REG_PORT_OUTCLR1 = 0x40000000;  /* turn on LED0 */
        else
            REG_PORT_OUTSET1 = 0x40000000;  /* turn off LED0 */
    }
}

/* this function initializes PortB7-0 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) {
    int i;
    unsigned char* ARRAY_PORT_PINCFG1 = (unsigned char*)&REG_PORT_PINCFG1;

    REG_PORT_DIRSET1 = 0x0000000F;	/* PB03-00 output */
	REG_PORT_DIRCLR1 = 0x000000F0;	/* PB07-04 input */
    for (i = 4; i < 8; i++)
        ARRAY_PORT_PINCFG1[i] |= 6; /* enable PB07-04 input buffer with pull */
    REG_PORT_OUTSET1 = 0x000000F0;	/* PB07-04 pull-up */
}

/* This is a non-blocking function.
 * If a key is pressed, it returns 1. Otherwise, it returns a 0.
 */

char keypad_kbhit(void) {
    int col;

    REG_PORT_DIRSET1 = 0x0F;    /* make all row pins output */
    REG_PORT_OUTCLR1 = 0x0F;    /* drive all row pins low */
    delay();                    /* wait for signals to settle */
    col = REG_PORT_IN1 & 0xF0;  /* read all column pins */
    REG_PORT_OUTSET1 = 0x0F;    /* drive all rows high before disable them */
    REG_PORT_DIRCLR1 = 0x0F;    /* make all row pins input */
    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) {
    __asm("nop");
}