From a15dbde2369e02c7d5926e76049e0cd04dd75154 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Thu, 10 Nov 2022 02:14:03 -0500
Subject: Add memory check segment, make display list show all 170 gr8 lines.

---
 dla.s | 48 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/dla.s b/dla.s
index e1429e9..130659f 100644
--- a/dla.s
+++ b/dla.s
@@ -12,6 +12,7 @@
  .include "nextpage.inc"
 
  loadaddr = $2000
+ lowcode = $0600 ; memcheck and io.s
  screen = $4000 ; must be on a x000 (4K) boundary
  screen2 = screen + $1000 ; rest of screen RAM after 4K boundary
  pixarray = screen + $20
@@ -52,9 +53,39 @@ cloksav:      .res 3 ; hold RTCLOK here while we convert to MM:SS.CC
 fptmp:        .res 6 ; used in mmss.s
 
  .code
- xex_org loadaddr
+
+ ;;; init xex segment: check that there's enough memory.
+ xex_org lowcode
  .include "io.s" ; printchrx and getchrx
  .include "printint.s"
+
+memcheck:
+ lda RAMTOP
+ cmp #$c0 ; 48K
+ bcs mem_ok
+ lda #<memmsg
+ ldx #>memmsg
+ jsr printmsg
+ lda RAMTOP ; free RAM in pages, divide by 4 to get K
+ lsr
+ lsr
+ jsr printdecb
+ lda #<memmsg2
+ ldx #>memmsg2
+ jsr printmsg
+mem_bad:
+ jmp mem_bad ; TODO: find a way to return to DOS from here
+mem_ok:
+ rts
+
+memmsg: .byte "Need 48K, only have ",0
+memmsg2: .byte "K.",$9b,"Disable BASIC, remove cartridge?",$9b,0
+
+ xex_init memcheck
+
+ ;;; main xex segment: the actual program. the functions in io.s
+ ;;; and printint.s are still in low memory.
+ xex_org loadaddr
  .include "mmss.s"
 
  ; init stuff gets done once, at startup
@@ -453,6 +484,8 @@ plot:
  sta (pixptr),y
  rts
 
+ ; drunkwalk is less than a page long. nextpage macro starts it
+ ; on a page boundary, so branches don't cost an extra cycle.
  nextpage
  .include "drunkwalk.s"
 
@@ -631,9 +664,10 @@ seeds_h: .byte >(seed_point-1),>(seed_plus-1),>(seed_4pt-1),>(seed_long-1)
  ; dlatbl.s is generated by perl script, mkdlatbl.pl
  .include "dlatbl.s"
 
- ; table of addresses, for each line on the screen. bloats the
- ; code by 384 bytes, but compared to calculating the address, is
- ; twice as fast!
+ ; table of addresses, for each line on the screen.
+ ; these 2 tables (low and high bytes) are less than a page each.
+ ; nextpage macro guarantees they don't cross a page boundary (so
+ ; indexed addressing doesn't cost an extra cycle).
  nextpage
 lineaddrs_l:
  laddr .set pixarray
@@ -653,6 +687,7 @@ lineaddrs_h:
 ;;; display list
  ; ANTIC opcodes
  blank8 = $70
+ blank3 = $20
  gr8    = $0f
  gr0    = $02
  lms    = $40
@@ -660,7 +695,7 @@ lineaddrs_h:
 
  xex_org dlist
  .byte blank8, blank8, blank8
- .byte blank8
+ .byte blank8, blank3
  .byte gr8 | lms
  .word screen
  .repeat 127
@@ -668,9 +703,10 @@ lineaddrs_h:
  .endrep
  .byte gr8 | lms
  .word screen2
- .repeat maxlines - 132
+ .repeat maxlines - 129
   .byte gr8
  .endrep
+ .byte blank3
  .byte gr0 | lms
  .word textbuf
  .byte jvb
-- 
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