From 9dd8d53ebad391ea40bcde76474b81b78a83e6a5 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Wed, 2 Nov 2022 15:18:42 -0400
Subject: Check for Start key in vblank only.

---
 dla.s | 41 +++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/dla.s b/dla.s
index 849bb23..927acb8 100644
--- a/dla.s
+++ b/dla.s
@@ -84,6 +84,12 @@ init:
  lda #>DEFAULTPART
  sta maxparticles+1
 
+ ; init our immediate vblank handler
+ lda #6
+ ldy #<consol_isr
+ ldx #>consol_isr
+ jsr SETVBV
+
  ; "New" option jumps here, restore GR.0 screen
 getargs:
  jsr restore_gr0
@@ -162,6 +168,7 @@ wl:
  lda #1 ; ...turn off shadow reg updates (tiny speed boost)
  sta CRITIC
  lda #0
+ sta DMACTL
  sta particles
  sta particles+1
  sta RTCLOK
@@ -532,17 +539,6 @@ checkbounds:
  beq oob
  sta cursor_y
 
- ldx #0
- lda CONSOL
- cmp #6
- bne dontplot
- jsr plot
- jsr unplot
- ldx #DMA_ON
-dontplot:
- ;stx SDMCTL ; nope, shadow updates are off...
- stx DMACTL
-
  ; check neighbors. used to be a subroutine, inlined it.
  ; also inlined plotsetup here.
  ldx cursor_y
@@ -563,7 +559,6 @@ dontplot:
  beq check_y
 slow_x:
  ; (-1,0)
- ldx cursor_x
  ldy xoffsets-1,x
  lda xmasks-1,x
  and (pixptr),y
@@ -725,6 +720,28 @@ close1:
  sta ICCOM,x
  jmp CIOV
 
+;;; Interrupt handler: consol_isr
+;;; Called via immediate IRC. Enables/disables ANTIC DMA based
+;;; on the status of the Start key, but only while CRITIC is set.
+consol_isr:
+ ;pha
+ ;txa
+ ;pha
+ lda CRITIC
+ beq ci_done
+ ldx #0
+ lda CONSOL
+ cmp #6
+ bne ci_nopress
+ ldx #DMA_ON
+ci_nopress:
+ stx DMACTL
+ci_done:
+ ;pla
+ ;tax
+ ;pla
+ jmp SYSVBV
+
 ;;;;; end of executable code, data tables from here on out.
 
 ; prompts.
-- 
cgit v1.2.3