#define PBIN (volatile unsigned char *) 0xFFFFFFF3
#define PBOUT (volatile unsigned char *) 0xFFFFFFF4
#define PBDIR (volatile unsigned char *) 0xFFFFFFF5
#define PCONT (volatile unsigned char *) 0xFFFFFFF7
#define CNTM (volatile unsigned char *) 0xFFFFFFD0
#define CTCON (volatile unsigned char *) 0xFFFFFFD8
#define CTSTAT (volatile unsigned char *) 0xFFFFFFD9
#define IVECT (volatile unsigned char *) 0x20
/*Setup should all be same as part A but need a few more vars*/
interrupt void intserv();

int main() {
    char digit = 0;     /*Digit for disp*/

    *PBDIR = 0xF0;      /*Port B dir as output */
    *CTCON = 0x2;       /*Stop Timer*/
    *CSTAT = 0x0;       /* Clear 'reached 0' flag*/
    *CNTM = 100000000;  /*Initialize timer */
    *PBOUT = 0x0;           /*Display 0*/

    *IVECT = (unsigned int * ) &intserv; /*Set Interuppt vec*/
    asm("MoveControl PSR, #0x40");      /*CPU responds to IRQ*/
    *PCONT = 0x40;                      /*Enable PBIN interrupts*/


    while(1) {
        while((*CTSTAT & 0x1) == 0);
        *CSTAT = 0x0;
        digit = (digit + 1)%10;
        *PBOUT = digit << 4;
    }

    exit(0);
}

interrupt void intserv() {
    unsigned char sample; /*Port B input sample*/
    sample = *PBIN & 0x3; /*Sample PBIN, isolate bits [1:0] */
    if (sample == 0x1) *CTCON = 0x1; /*start timer*/
    else if (sample == 0x2) *CTCON = 0x2; /*Stop timer*/

}