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mem: reserve top 4 physical pages for the NMI break monitor #147

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Merged
mbrukner merged 3 commits into from
Jul 17, 2026
Merged

mem: reserve top 4 physical pages for the NMI break monitor #147

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mem: cap program pages at $3e, reserve $3f for the NMI break monitor
mbrukner Jul 10, 2026
e581d10
mem: reserve $3d-$3f (MaxPhysPage=60) for NMI monitor screen-save + code
mbrukner Jul 10, 2026
e1f2e3a
reserve bank $3c for the 2-bank break monitor (MaxPhysPage 60->59)
mbrukner Jul 13, 2026
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2 changes: 1 addition & 1 deletion source/system.f256/memory/memory.flat/memory.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -233,7 +233,7 @@ maxUsablePages: ; runtime max logical pages (updated by LOMEM)

ProgramPage0 = BasicStart >> 13 ; physical page for slot 1 at boot (identity mapping)
FirstFreePage = 48 ; first safe physical page for program data ($60000)
MaxPhysPage = 64 ; 512KB = 64 × 8KB pages
MaxPhysPage = 59 ; highest usable 8KB page: RAM has 64 pages ($00-$3f), top 4 ($3c-$3f) reserved for the 2-bank NMI break monitor (screen save ×2 + code ×2)
_AvailablePages = MaxPhysPage - FirstFreePage + 1 ; dynamic pages + page 0
.if _AvailablePages < MaxPages
MaxUsablePages = _AvailablePages
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