// source code for the mega16 or mega32.  This processor will read the sync pulses on
// the ELM304, and then update a counter when it is time to display pixels.  This counter
// will point directly to an address on the 32K memory chips.


// DO NOT CHANGE ANY OF THIS UNLESS YOU KNOW WHAT YOU ARE DOING.
// IT MAY BE POSSIBLE TO HAVE THIS CHIP DO SMALL TASKS, DURING THE DOWN TIME
// BUT THE CODE SHOULD NOT BE ALTERED UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING

#include <mega32.h>
//#include <delay.h>

#define DISPLAY_ON PIND.7
#define DISPLAY_READY PIND.6
#define MEM_OE PORTD.5
#define DAC_ACTIVE PORTD.4


// global variables
// Display variables
register unsigned int pixelAddress @4;

unsigned char i, displayFlag, repeatFlag, firstDisplay;


#asm
; Port definitions

; ***** I/O REGISTER DEFINITIONS *****************************************
; NOTE:
; Definitions marked "MEMORY MAPPED"are extended I/O ports
; and cannot be used with IN/OUT instructions
.equ	PORTA	= 0x1b
.equ	DDRA	= 0x1a
.equ	PINA	= 0x19
.equ	PORTB	= 0x18
.equ	DDRB	= 0x17
.equ	PINB	= 0x16
.equ	PORTC	= 0x15
.equ	DDRC	= 0x14
.equ	PINC	= 0x13
.equ	PORTD	= 0x12
.equ	DDRD	= 0x11
.equ	PIND	= 0x10

; ***** CPU REGISTER DEFINITIONS *****************************************
.def	XH	= r27
.def	XL	= r26
.def	YH	= r29
.def	YL	= r28
.def	ZH	= r31
.def	ZL	= r30
#endasm

interrupt [EXT_INT0] void ext_int0(void)
{    
    unsigned char timer1 = 0;
    while (timer1<11)	// wait for back porch to finish
    {
        timer1++;
    }
    
    
    if (DISPLAY_ON == 1)
    {    
        
        // check if mega128 is done with sram
        if (DISPLAY_READY == 1 && firstDisplay == 0)	// added this check so it will not start displaying halfway through a frame
        {
            // set display flag
            displayFlag = 1;
            PORTD.1 = 0;   
        }
        else
        {
            displayFlag = 0;
            firstDisplay = 1;
        }
    ////////////////////////////
    //******Display Code******//
    ////////////////////////////
        if (displayFlag == 1)
        {
            
            // turn on Memory output
            MEM_OE = 0;
            
            // set ports for output
            DDRA = 0xFF;
            DDRC = 0xFF;
            DAC_ACTIVE = 0; // ON
            
            #asm                        
            .MACRO singlePixel
            out PORTA, r4
            inc r4
            nop
            ;nop
            .ENDMACRO
            
            .MACRO fivePixels
            singlePixel
            singlePixel
            singlePixel
            singlePixel
            singlePixel
            .ENDMACRO
            
            .MACRO fiftyPixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            fivePixels
            .ENDMACRO
            
            .MACRO Two55Pixels
            fiftyPixels
            fiftyPixels
            fiftyPixels
            fiftyPixels
            fiftyPixels
            fivePixels
            .ENDMACRO
            
            out PORTC, r5       ; go to correct line in memory
            Two55Pixels         ; push out pixels by incrementing PORTA
            inc r5              ; go to next line in memory
            clr r4             ; reset pixel count
            
            #endasm
            if (repeatFlag == 0)
            {
                repeatFlag = 1;
                #asm
                dec r5
                #endasm
            }
            else
                repeatFlag = 0;
                
            // Turn off mem_oe
            MEM_OE = 1;
            DAC_ACTIVE = 1; // OFF
            // Set ports in high-Z state
            DDRA = 0x00;
            DDRC = 0x00;
            PORTA = 0x00;
            PORTC = 0x00;
        }    
    }
    else    // WHITE_ON == 0
    {
    // Tell the mega128 display is done
    PORTD.1 = 1;	
    // restart pixel count
    pixelAddress = 0;
    firstDisplay = 0;
    }
}   
    
void initialize(void)
{     
    pixelAddress = 0;
    //turn off memory output
    MEM_OE = 1;

	// PortA Low address
    DDRA = 0x00;

	// PortC high address
	DDRC = 0x00;

	// PortD will be used to take in the sync pulses, the external interrupt on bit2 is active
	// also used to test for incoming stuff from mega128 and v2 on the elm304
	// also, pin 5 is used for MEM_OE
	// also pin 4 used to turn DAC on and off
	DDRD = 0b00110010;
	PORTD = 0b00110000;

    /*****Interrupts and Timers*****/
	
	// Set Timer0 Control Register, no prescaler
	TCCR0 = 0x01;
	
	// Set interrupt 0  to register on rising edge (horizontal sync is a falling edge, followed by a rising edge)
	// Idle sleep mode also set
	MCUCR = 0b00000011;

	// Enable external interrupt 0 to seach for sync pulses.
    	GICR = 0b01000000;         
}

void main(void)
{
    initialize();
    #asm
    	sei
    #endasm
    while(1)
    {
    	#asm
    		sleep
    	#endasm
	}
}