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Add rom, ram2 bank memory; modify read/write sig

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The signature for read/write map functions now accepts a void pointer so
that we can pass in the machine that those functions may need to know
about. This is a bit hairy, but allows us to avoid the need for a
yet-uglier global variable.
This commit is contained in:
Peter Evans 2018-01-02 16:24:51 -06:00
parent 49d475d534
commit 834959c10a
2 changed files with 68 additions and 0 deletions
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48
include/apple2.h
View File

@ -6,6 +6,21 @@
#include "vm_bitfont.h"
#include "vm_screen.h"
/*
* The size of our block of ROM is 12k
*/
#define APPLE2_ROM_SIZE 0x3000
/*
* Whereas the second bank of RAM is a mere 4k
*/
#define APPLE2_RAM2_SIZE 0x1000
/*
* This is the base address (or offset) for all bank-switched memory
*/
#define APPLE2_BANK_OFFSET 0xD000
enum video_modes {
VIDEO_40COL_TEXT,
VIDEO_LORES,
@ -41,6 +56,17 @@ enum lores_colors {
LORES_WHITE,
};
/*
* These are the potential memory modes we understand. You can only have
* one memory mode at a time.
*/
enum memory_mode {
MEMORY_BANK_ROM, // the last 12k is system ROM
MEMORY_BANK_RAM1, // the last 12k is system RAM
MEMORY_BANK_RAM2, // the first 4k of the last 12k is a separate RAM
// block from that in RAM1
};
typedef struct {
/*
* The apple 2 hardware used an MOS-6502 processor.
@ -54,6 +80,21 @@ typedef struct {
*/
vm_segment *memory;
/*
* The Apple II used a system of bank-switched memory to enable
* software to address a separate block of ROM.
*/
vm_segment *rom;
/*
* Additionally, the Apple II had a standalone block of RAM (with no
* good name for it, really, hence the regrettably vague "ram2") so
* that you technically could use 16k of RAM from a set of 12k
* addresses. The extra 4k lives a lonely life in the garage
* apartment.
*/
vm_segment *ram2;
/*
* The screen wherein we shall render all of our graphics.
*/
@ -80,6 +121,13 @@ typedef struct {
*/
int color_mode;
/*
* This describes the behavior of our bank-switching scheme. We need
* our read/write mappers to know where writes into the
* bank-switched area of memory should target.
*/
int memory_mode;
/*
* Our two disk drives.
*/

20
src/apple2.c
View File

@ -39,6 +39,8 @@ apple2_create(int width, int height)
// Forward set these to NULL in case we fail to build the machine
// properly; that way, we won't try to free garbage data
mach->rom = NULL;
mach->ram2 = NULL;
mach->sysfont = NULL;
mach->screen = NULL;
mach->drive1 = NULL;
@ -51,8 +53,18 @@ apple2_create(int width, int height)
return NULL;
}
// Our memory is that which is owned by the CPU.
mach->memory = mach->cpu->memory;
// Initliaze our system ROM and separate bank-switched block of RAM
mach->rom = vm_segment_create(APPLE2_ROM_SIZE);
mach->ram2 = vm_segment_create(APPLE2_RAM2_SIZE);
if (mach->rom == NULL || mach->ram2 == NULL) {
log_critical("Could not initialize ROM / RAM2!");
apple2_free(mach);
return NULL;
}
// Our two drives -- we create both of them, even if we intend to
// use only one.
mach->drive1 = apple2dd_create();
@ -179,6 +191,14 @@ apple2_free(apple2 *mach)
mos6502_free(mach->cpu);
}
if (mach->rom) {
vm_segment_free(mach->rom);
}
if (mach->ram2) {
vm_segment_free(mach->ram2);
}
if (mach->sysfont) {
vm_bitfont_free(mach->sysfont);
}