// Handel-C decade counter and test - for the Altera NIOS board

void increment_decade(unsigned 4 *count, unsigned 1 Hold);
unsigned 8 sevenseg(unsigned 4 bcd);

set clock = external "L6" with { rate = 33 };	// 33.333 MHz

void main (void)
{
	// Declarations
	unsigned 1 stop;
	unsigned 4 count[2];
	unsigned 1 hold;
	unsigned 24 cycles;
	unsigned 8 seg1, seg2;

	// Hardware interface

	// Seven segment display 1
	interface bus_out () display1 (unsigned 8 out = seg1)
		with { data = {"D18", "V17", "V18", "Y17", "V8", "Y7", "U11", "R11"} };

	// Seven segment display 2
	interface bus_out () display2 (unsigned 8 out = seg2)
		with { data = {"C18", "W17", "U18", "Y18", "W18", "U8", "T11", "R10"} };

	// Initialisation
	par {
		stop = 0;
		count[0] = 0;
		count[1] = 0;
	}

	par {

		// Cycle counter - use this to divide the clock
		while (!stop) par {
			cycles++;
			hold = (cycles != 0xffffff);
		}

		// Call the counter
		while (!stop)
			increment_decade(count, hold);

		// Seven segment displays (active low) - musn't call these in parallel!
		while (!stop) {
			seg1 = sevenseg(count[1]);
			seg2 = sevenseg(count[0]);
		}
	}

}

// This function describes a two digit BCD counter

void increment_decade(unsigned 4 *count, unsigned 1 Hold)
{
	if (Hold)
		count[0] = count[0];		/* You have to do something! */
	else if ( count[0] == 9 ) par {	/* "par" ensures one cycle */
		count[0] = 0;
		if ( count[1] == 9 )
			count[1] = 0;
		else
			count[1]++;
	} else
		count[0]++;
}

// This function describes a BCD to seven-segment encoder.
// The display inputs are active low. At 33 MHz, it doesn't matter
// that this takes two clocks to execute.

unsigned 8 sevenseg(unsigned 4 bcd)
{
	unsigned 8 seg;
	switch (bcd) {
		case 0:
			seg = 0b11000000;
			break;
		case 1:
			seg = 0b11111001;
			break;
		case 2:
			seg = 0b10100100;
			break;
		case 3:
			seg = 0b10110000;
			break;
		case 4:
			seg = 0b10011001;
			break;
		case 5:
			seg = 0b10010010;
			break;
		case 6:
			seg = 0b10000011;
			break;
		case 7:
			seg = 0b11111000;
			break;
		case 8:
			seg = 0b10000000;
			break;
		case 9:
			seg = 0b10011000;
			break;
		default:
			seg = 0b01110111;
			break;
	}

	return seg;
}