114 lines
2.1 KiB
C
114 lines
2.1 KiB
C
#include "inc/types.h"
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#include "inc/rom.h"
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#include "inc/basic.h"
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#include "inc/memory.h"
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/*
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memory model:
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+ - - - - +
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| 0000 |
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| RAM |
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| 7FFF |
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+ - - - - +
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. . .
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unused
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. . .
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+ - - - - +
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| FF00 |
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| ROM |
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| FFFF |
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+ - - - - +
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*/
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db ram_memory[32 * 1024]; // total memory: 32KB
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db keyboard_buffer; // 0xD010
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db keyboard_control; // 0xD011
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db display_buffer; // 0xD012
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db display_control; // 0xD013
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db read_byte(dw address)
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{
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if (address >= 0x0000 && address <= 0x7FFF)
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{
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// 32KB memory RAM
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return ram_memory[address];
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}
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else if (address == 0xD010)
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{
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// when reading from keyboard buffer,
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// its status control is disabled again
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keyboard_control = 0x00;
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return keyboard_buffer;
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}
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else if (address == 0xD011)
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{
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return keyboard_control;
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}
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else if (address == 0xD012)
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{
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return display_buffer;
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}
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else if (address >= 0xE000 && address <= 0xEFFF)
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{
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// BASIC
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address = address & 0xFFF;
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return basic_memory[address];
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}
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else if (address >= 0xFF00 && address <= 0xFFFF)
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{
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// wozmon ROM
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address = address & 0x00FF;
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return rom_memory[address];
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}
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else
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{
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// unused memory
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return 0x00;
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}
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}
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dw read_word(dw address)
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{
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dw word;
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db low_byte;
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db high_byte;
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low_byte = read_byte(address);
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high_byte = read_byte(address + 1);
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word = high_byte << 8; // shifts high byte to its place
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word = word | low_byte; // appends low byte to form the complete word
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// the word is store in little-endian format on the memory
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return word;
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}
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void write_mem(dw address, db data)
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{
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if (address >= 0x0000 && address <= 0x7FFF)
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{
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// 32KB memory RAM
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ram_memory[address] = data;
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}
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else if (address == 0xD012)
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{
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display_buffer = data | 0x80;
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}
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// any other addressed memory will be ignored on write
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}
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