address.c

#include <stdio.h>
#include <stdlib.h>
#include "header.h"
#include "screen.h"

unsigned char lang_ROM[0x4000]; // reserve 16K for the language ROM data
unsigned char OS_ROM[0x4000];   // reserve 16K for the OS_ROM data

void (*screen_byte_P)(ubyte, uint);


/*
This function is _always_ used to access an address unless it is in the
zero page or the stack, then it may be directly accessed in the RAM[]
*/
ubyte getbyte(uint address) {

    if (address < 0x8000) return RAM[address];
    // If address is below the 32K mark access the RAM


    if (address < 0xC000) return (romsel == 0xC ? lang_ROM[address - 0x8000] : (ubyte) 0xFF);
    // If address is below the 48K mark access the language ROM
    if ((address > 0xFEFF) || (address < 0xFC00)) return OS_ROM[address - 0xC000];
    // If address is outside the 3 pages of memmapped io,
    // access the OS_ROM
    return ((address & 0xFF00) == 0xFE00) ? rsheila[(char) (address)]() : (ubyte) 0xff;

}                    // the address must be in the 3 pages of memmapped io.


/*
This functions is always used to write to an address unless it is
known for certain to exist with the zeropage/stack range.
(when it may be accessed directly through the RAM[]).
*/

void putbyte(ubyte byte, uint address) {
    if (address < 0x8000) {
        if (address >= ram_screen_start)  // if screen RAM
            screen_byte_P(byte, address); // output screen data

        RAM[address] = byte;              // update RAM
    }

    else if ((address & 0xFF00) == 0xFE00) wsheila[(char) (address)](byte);

    else if ((address < 0xFC00) || (address > 0xFEFF)) {
        // Since this is an impossible situation, a crash probably has occured
        // therefore display error and exit
        printf("\nROM write attempt at %X", address);
        exit(1);
    }
}


void init_mem(void)     // initialise the 6502 memory space
{
    FILE *fp1;           // misc files pointers
    FILE *fp2;
    unsigned int c;      // misc loop counter

    for (c = 0; c < 0x8000; c++) {
        RAM[c] = 0;         // intiialise the 6502 emulator RAM
    }

    printf("Opening ROM Image files..."); // display pretty startup status
    if ((fp1 = fopen("roms/os.bin", "rb")) == NULL) {
        printf("\nError: Could not open OS_ROM image.");
        exit(1);    // exit abnormally
    }
    if ((fp2 = fopen("roms/basic.bin", "rb")) == NULL) {
        printf("\nError: Could not open lang_ROM image.");
        exit(1);    // exit abnormally
    }
    printf("Done\n"); // display pretty status status


    printf("Reading ROM Image data..."); // display pretty startup status
    for (c = 0; c < 0x4000; c++)   // initialise the ROM blocks
    {
        OS_ROM[c] = (ubyte) getc(fp1);    // read data from the image files
        lang_ROM[c] = (ubyte) getc(fp2);  //

        if ((ferror(fp2)) || (ferror(fp1))) {
            printf("\nFatal Error:- Rom image file error");
            exit(1);          // exit abnormally if there is a file error
        }
    }
    printf("Done\n");    // display pretty startup status

    printf("Closing ROM Image files...");
    fclose(fp1);
    fclose(fp2);          // close the image files
    printf("Done\n");

}