ELEC 371 2017 final Q7

#include <stdint.h>
#include <nios2_control.h>

#define TIMER ((volatile uint32_t *)0x5000)
#define INPUT ((volatile uint32_t *)0x6a00)
#define OUTPUT ((volatile uint32_t *)0x7e00)
#define JTAG_UART ((volatile uint32_t *)0xa800)

#define TIMER_INT (1 << 0)

#define F_CPU (50000000)
#define TIMER_CYCLES ((int)(0.5 * F_CPU))

void Init(void) {
    OUTPUT[0] = INPUT[0] & 0xff00 | 0x0f;

    TIMER[0] = 0; /* clear extraneous interrupt */
    TIMER[2] = TIMER_CYCLES & 0xffff;
    TIMER[3] = TIMER_CYCLES >> 16;
    TIMER[1] = 0b0111;

    NIOS2_WRITE_IENABLE(TIMER_INT);
    NIOS2_WRITE_STATUS(1);
}

void PrintChar(unsigned int ch) {
    while((JTAG_UART[1] & 0xffff0000) == 0) {}
    JTAG_UART[0] = ch & 0xff;
}

void PrintHexDigit(unsigned int n) {
    unsigned int use;
    if (n < 10)
        use = n + '0';
    else
        use = n - 10 + 'A';
    PrintChar(use);
}

void UpdateLEDs(void) {
    OUTPUT[0] ^= 0xff;
}

int timercount = 0, timerflag = 0;

void interrupt_handler(void) {
    uint32_t ipending = NIOS2_READ_IPENDING();
    if(ipending & TIMER_INT) {
        UpdateLEDs();
        if(++timercount >= 10 * 2) {
            timercount = 0;
            timerflag = 1;
        }
    }
}

int main(void) {
    Init();

    while(1) {
        if(INPUT[0] & 0x80) {
            uint32_t data = INPUT[0] & 0x7f;
            while(INPUT[0] & 0x80) {}
            data >>= 3;
            PrintHexDigit(data);
            PrintChar(0x0d);
        }
        if(timerflag) {
            timerflag = 0;
            OUTPUT[0] = INPUT[0] & 0xff00 | OUTPUT[0] & 0xff;
        }
    }
    /*
        some compilers will get unhappy
        if there is no return
    */
    return 0;
}