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update comments about RAM page handling

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Jorj Bauer 2020-07-02 22:00:30 -04:00
parent ff486ee0d4
commit 48ef6a4dea
1 changed files with 3 additions and 10 deletions
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apple/applemmu.cpp
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@ -60,15 +60,8 @@ Current write page table [512 bytes] in real ram
*/
// All the pages. Because we don't have enough RAM for both the
// display's DMA and the Apple's 148k (128k + ROM space), we're using
// an external SRAM for some of this. Anything that's accessed very
// often should be in the *low* pages, b/c those are in internal
// Teensy RAM. When we run out of preallocated RAM (cf. vmram.h), we
// fall over to an external 256kB SRAM (which is much slower).
//
// Zero page (and its alts) are the most used pages (the stack is in
// page 1).
// This has a split memory model so more often addressed pages can be
// in internal memory, and an external memory can hold others.
//
// We want the video display pages in real RAM as much as possible,
// since blits wind up touching so much of it. If we can keep that in
@ -85,7 +78,7 @@ enum {
MP_ZP = 0, // page 0/1 * 2 page variants = 4; 0..3
MP_4 = 4, // 0x04 - 0x07 (text display pages) * 2 variants = 8; 4..11
MP_20 = 12, // 0x20 - 0x5F * 2 variants = 128; 12..139
// Pages that can go to external SRAM:
// Pages that can go to external RAM if needed:
MP_2 = 140, // 0x02 - 0x03 * 2 variants = 4; 140..143
MP_8 = 144, // 0x08 - 0x1F * 2 = 48; 144..191
MP_60 = 192, // 0x60 - 0xBF * 2 = 192; 192..383