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Diffstat (limited to 'vcount.s')
| -rw-r--r-- | vcount.s | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/vcount.s b/vcount.s new file mode 100644 index 0000000..067ce26 --- /dev/null +++ b/vcount.s @@ -0,0 +1,22 @@ + .export _waitvcount + + .include "atari.inc" + +; wait for VCOUNT to reach a particular value. Use this +; to avoid updating parts of the screen while ANTIC is +; reading from it. + +; c should be ((4 + Yposition) * 4), where Yposition is +; the text line below the bottom one you're about to modify. + +; void __fastcall__ waitvcount(unsigned char *c) +_waitvcount: + sta FR1 + +w: + lda VCOUNT + cmp FR1 + bne w + + STA WSYNC ; finish current scanline + rts |