[cc65] c64 question

Date view Thread view Subject view

From: Arvid Norberg (c99ang_at_cs.umu.se)
Date: 2001-03-06 12:17:25 

Hello,

I'm sorry to a post computer-specific question here, but you guys are 
my last hope.. ;)

What I'm trying to do is to scroll the lines 100 through 150 by using a 
raster-interrupt (two actually). But I can't get it to work.

My questions are:

What am I missing? why doesn't it work the way I want it to?
If I want to make a function that ends with an "rti" instead of "rts", 
is there a keyword/modifier in cc65 that does that to a function?
in some compilers you can to write:

interrupt void IRQ_handler(void)
{
	...
}

ok then, here's the source:
-------------------

#include <c64.h>
#include <6502.h>

#define irq_vector (*(void**)0x314)

void IRQ_handler_bottom();
void IRQ_handler_top();
void main();

void IRQ_handler_top()
{
	if (VIC.irr & 1) // make sure we got a raster interrupt
	{
		static unsigned char a = 0;
		a = (a + 1) & 7; // increase the scroll-counter

		// select 38 column mode and scroll this part of the screen 'a' 
pixels
		VIC.ctrl2 = a;

		// let the next interrupt handler get executed on line 150
		irq_vector = IRQ_handler_bottom;
		VIC.rasterline = 150;
		
		// tell the VIC-chip that we have handled the interrupt
		VIC.irr &= ~1;
	}

	// jump to the standard interrupt routine
	__asm__("	jmp	$ea31");
}

void IRQ_handler_bottom()
{
	if (VIC.irr & 1) // make sure we got a raster interrupt
	{
		// select 40 columns mode and 
		VIC.ctrl2 = 0x8;

		// let the first interrupt handler get executed on line 100
		irq_vector = IRQ_handler_top;
		VIC.rasterline = 100;

		// tell the VIC-chip that we have handled the interrupt
		VIC.irr &= ~1;
	}

	// jump to the standard interrupt routine
	__asm__("	jmp	$ea31");
}


void main()
{
	SEI(); // make sure we don't get an interrupt while we are setting 
up our own
	
	irq_vector = IRQ_handler_top;

	CIA1.icr = 0x7f;
	VIC.imr = 1;			// enable raster IRQ
	VIC.rasterline = 100;	// the line where we want to get an 
interrupt

	CLI(); // enable interrupts again

	while (1); // just wait here
}


---
Arvid Norberg
----------------------------------------------------------------------
To unsubscribe from the list send mail to majordomo_at_musoftware.de with
the string "unsubscribe cc65" in the body(!) of the mail.

Date view Thread view Subject view

This archive was generated by hypermail 2.1.3 : 2001-12-14 22:05:39 CET