From 48ef6a4dea6d74bb7825a5db0920854a8dd936ec Mon Sep 17 00:00:00 2001 From: Jorj Bauer Date: Thu, 2 Jul 2020 22:00:30 -0400 Subject: [PATCH] update comments about RAM page handling --- apple/applemmu.cpp | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) diff --git a/apple/applemmu.cpp b/apple/applemmu.cpp index 46b74b8..e00a692 100644 --- a/apple/applemmu.cpp +++ b/apple/applemmu.cpp @@ -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