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UpdatePaging(): improve comment for page0 & page1 and memdirty

This commit is contained in:
tomcw 2024-01-20 18:57:27 +00:00
parent 529b1a8a83
commit 59a535d213
1 changed files with 5 additions and 2 deletions
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7
source/Memory.cpp
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@ -1258,8 +1258,11 @@ static void UpdatePaging(BOOL initialize)
// PAGING SHADOW TABLE
//
// NB. the condition 'loop <= 1' is there because:
// . Page0 (ZP) : memdirty[0] is set when the 6502 CPU does a ZP-write, but perhaps older versions didn't set this flag (eg. the asm version?).
// . Page1 (stack) : memdirty[1] is NOT set when the 6502 CPU writes to this page with JSR, etc.
// . Page0 (ZP) and Page1 (stack) are written to so often that it's almost certain that they'll be dirty every time this function is called.
// Note also that:
// . Page0 (ZP) : memdirty[0] is set when the 6502 CPU writes to ZP.
// . Page1 (stack) : memdirty[1] is NOT set when the 6502 CPU writes to this page with JSR, PHA, etc.
// Ultimately this is an optimisation (due to Page1 writes not setting memdirty[1]) and Page0 could be optimised to also not set memdirty[0].
for (loop = 0x00; loop < 0x100; loop++)
{