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Fix check whether there is enough memory btw. MEMLO and the program

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load address to move screen buffer there.
This commit is contained in:
Christian Groessler 2013-06-20 23:31:41 +02:00
parent 96b0ca0524
commit 6ed1b07e59
3 changed files with 101 additions and 30 deletions
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20
libsrc/atari/shadow_ram_prepare.s
View File

@ -107,26 +107,18 @@ sramprep:
ora #2
sta PORTB
.include "xlmemchk.inc"
; ... change system memory variables bla
CMPVAL = 64+255+992 ; you may ask, why these values... @@@ document
sys_ok: lda #<__SAVEAREA_LOAD__
sec
sbc #<CMPVAL
sta MEMTOP
sta APPMHI
lda #>__SAVEAREA_LOAD__
sbc #>CMPVAL
ldx tstadr2
stx MEMTOP
stx APPMHI
lda tstadr2+1
sta MEMTOP+1
sta APPMHI+1
lda #>__SAVEAREA_LOAD__ - 1
lda lowadr+1
sta RAMTOP
; ... issue a GRAPHICS 0 call (copied'n'pasted from TGI drivers)

20
libsrc/atari/system_check.s
View File

@ -90,27 +90,15 @@ is_xl: lda RAMSIZ
fail: jsr delay
jmp (DOSVEC)
lowadr: .res 2 ; lowest address we need in order to move screen memory down, depending on start address of program
; system is basically supported, check if there is enough space btw. MEMLO and our start address
; to move screen memory there
CMPVAL = 64+255+992 ; you may ask, why these values... @@@ document
sys_ok: lda #<__SAVEAREA_LOAD__
sec
sbc #<CMPVAL
sta lowadr
lda #>__SAVEAREA_LOAD__
sbc #>CMPVAL
sta lowadr+1
sys_ok:
.include "xlmemchk.inc"
sec
lda MEMLO
sbc lowadr
sbc tstadr2
lda MEMLO+1
sbc lowadr+1
sbc tstadr2+1
bcc memlo_ok
; load address was too low

91
libsrc/atari/xlmemchk.inc Normal file
View File

@ -0,0 +1,91 @@
; ... change system memory variables bla
jmp cont
lowadr: .word __SAVEAREA_LOAD__ & $FF00 ; our load address, rounded down to page boundary
tstadr: .res 2
tstadr2:.res 2
tmp: .res 1
; When setting a display mode, the ROM takes the RAMTOP value
; and subtracts the size of the screen memory from it. This will
; become the new screen memory address.
; From this address it subtracts the size of the display list.
; This will become the new display list address.
; Screen memory cannot cross 4K boundaries and a display list
; cannot cross a 1K boundary.
; Work out a sane value for RAMTOP to prevent boundary crossing.
; RAMTOP is only one byte, it counts in memory pages.
cont:
_SCRBUFSZ = (40 * 24) ; size of mode 0 screen buffer
_DLSZ = 32 ; size of mode 0 display list
; subtract screen memory size from our load address
lda lowadr
sec
sbc #<_SCRBUFSZ
sta tstadr
lda lowadr+1
sbc #>_SCRBUFSZ
sta tstadr+1
; check if a 4K boundary is crossed
lda lowadr+1
and #$f0
sta tmp
lda tstadr+1
and #$f0
cmp tmp
beq scrmemok
; 4K boundary will be crossed, take 4K boundary address as lowadr
al4k: lda lowadr+1
and #$f0
tax
dex
stx lowadr+1
bne cont
; subtract display list size from calculated screen address
scrmemok:
lda tstadr
sec
sbc #<_DLSZ
sta tstadr2
lda tstadr+1
sbc #>_DLSZ
sta tstadr2+1
; check if a 1K boundary is crossed
lda tstadr+1
and #$fc
sta tmp
lda tstadr2+1
and #$fc
cmp tmp
bne al4k ; 1K boundary will be crossed, decrease lowadr
; address of display list is ok
dlok:
; decrease tstadr2 by two
lda tstadr2
sec
sbc #2
sta tstadr2
bcs dec_cont
lda tstadr2+1
sbc #0
sta tstadr2+1
dec_cont: