mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-22 14:33:51 +00:00
38 lines
1.0 KiB
C
38 lines
1.0 KiB
C
|
|
/*
|
|
The Atari 7800 uses display lists and interrupts to
|
|
partition the video frame, but the 6502 can also be
|
|
synchronized with each scanline. When the CPU strobes
|
|
the WSYNC register, the CPU is halted until the end
|
|
of the current scanline. This is similar to the WSYNC
|
|
register on the Atari 2600, except that VBLANK and
|
|
VSYNC are automatically applied.
|
|
*/
|
|
|
|
#include "atari7800.h"
|
|
|
|
void main() {
|
|
byte y1 = 110; // Y start of bar
|
|
byte y2 = 10; // height of bar
|
|
byte i;
|
|
while (1) {
|
|
// wait for end of frame / start of vblank
|
|
while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
|
|
// wait for end of vblank / start of frame
|
|
while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
|
|
// skip scanlines until at top of bar
|
|
for (i=0; i<y1; i++) {
|
|
WSYNC();
|
|
}
|
|
// set the background color on each scanline
|
|
for (i=0; i<y2; i++) {
|
|
MARIA.BACKGRND = P6532.SWCHA - i;
|
|
WSYNC();
|
|
}
|
|
// clear the background after the final scanline
|
|
MARIA.BACKGRND = 0;
|
|
// move bar slowly downward
|
|
y1++;
|
|
}
|
|
}
|