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atarixl: check at startup whether RAM beneath the ROM is in use

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If detected, the program refuses to run, preventing a crash.
The check only works with SpartaDOS. I don't have an overview which
DOSes potentially use the RAM under the ROM. Or which other installed
programs might use it.

No additional runtime memory space is consumed, since the change
is in the "system check" load chunk which gets replaced by the
user program during loading.
This commit is contained in:
Christian Groessler 2018-09-12 01:05:52 +02:00
parent c7a40db1b7
commit e4e3dbf756
1 changed files with 31 additions and 2 deletions
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33
libsrc/atari/system_check.s
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@ -68,8 +68,32 @@ cont: ldx #0 ; channel 0
.segment "SYSCHK"
rts ; for older DOSes which unconditionally run the first load chunk
.ifdef __ATARIXL__
; check for SpartaDOS and its usage of RAM below ROM
; return CF 0/1 for bad/ok
sdcheck:lda DOS
cmp #'S'
bne sdcrts0 ; not SpartaDOS, assume RAM is not used
lda DOS+1 ; SD version
cmp #$40 ; SD-X has $40 or higher
bcc sdcrts1 ; older versions (except maybe 1.x) always use the RAM under the ROM
ldy #31 ; offset for OSRMFLG
lda (DOSVEC),y ; get OSRMFLG
bne sdcrts1
sdcrts0:clc
rts
sdcrts1:sec
rts
ramrom_txt:
.byte "Memory under ROM is in use.", ATEOL
.byte "Cannot run this program.", ATEOL
ramrom_txt_len = * - ramrom_txt
lmemerrxl_txt:
.byte "Not enough memory to move screen", ATEOL
.byte "memory to low memory. Consider using", ATEOL
@ -94,8 +118,13 @@ syschk: lda $fcd8 ; from ostype.s
jmp mem_err
sys_ok:
.include "xlmemchk.inc" ; calculate lowest address we will use when we move the screen buffer down
sys_ok: jsr sdcheck ; check for SpartaDOS-X, and if found, whether it uses the RAM under the ROM
bcc sd_ok
print_string2 ramrom_txt, ramrom_txt_len
jmp fail
sd_ok: .include "xlmemchk.inc" ; calculate lowest address we will use when we move the screen buffer down
lda MEMLO
cmp lowadr