303 lines
11 KiB
C++
303 lines
11 KiB
C++
#include "Interpreter.hpp"
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#include <cstring>
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#include <stdexcept>
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namespace chocochip8 {
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// converts any 8-bit sprite row to its high-res 16-bit equivalent
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constexpr uint16_t gcvLowResToHighResRowLookupTable[256] = {
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0x0000, 0x0003, 0x000C, 0x000F, 0x0030, 0x0033, 0x003C, 0x003F, 0x00C0, 0x00C3, 0x00CC, 0x00CF, 0x00F0, 0x00F3, 0x00FC, 0x00FF,
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0x0300, 0x0303, 0x030C, 0x030F, 0x0330, 0x0333, 0x033C, 0x033F, 0x03C0, 0x03C3, 0x03CC, 0x03CF, 0x03F0, 0x03F3, 0x03FC, 0x03FF,
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0x0C00, 0x0C03, 0x0C0C, 0x0C0F, 0x0C30, 0x0C33, 0x0C3C, 0x0C3F, 0x0CC0, 0x0CC3, 0x0CCC, 0x0CCF, 0x0CF0, 0x0CF3, 0x0CFC, 0x0CFF,
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0x0F00, 0x0F03, 0x0F0C, 0x0F0F, 0x0F30, 0x0F33, 0x0F3C, 0x0F3F, 0x0FC0, 0x0FC3, 0x0FCC, 0x0FCF, 0x0FF0, 0x0FF3, 0x0FFC, 0x0FFF,
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0x3000, 0x3003, 0x300C, 0x300F, 0x3030, 0x3033, 0x303C, 0x303F, 0x30C0, 0x30C3, 0x30CC, 0x30CF, 0x30F0, 0x30F3, 0x30FC, 0x30FF,
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0x3300, 0x3303, 0x330C, 0x330F, 0x3330, 0x3333, 0x333C, 0x333F, 0x33C0, 0x33C3, 0x33CC, 0x33CF, 0x33F0, 0x33F3, 0x33FC, 0x33FF,
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0x3C00, 0x3C03, 0x3C0C, 0x3C0F, 0x3C30, 0x3C33, 0x3C3C, 0x3C3F, 0x3CC0, 0x3CC3, 0x3CCC, 0x3CCF, 0x3CF0, 0x3CF3, 0x3CFC, 0x3CFF,
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0x3F00, 0x3F03, 0x3F0C, 0x3F0F, 0x3F30, 0x3F33, 0x3F3C, 0x3F3F, 0x3FC0, 0x3FC3, 0x3FCC, 0x3FCF, 0x3FF0, 0x3FF3, 0x3FFC, 0x3FFF,
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0xC000, 0xC003, 0xC00C, 0xC00F, 0xC030, 0xC033, 0xC03C, 0xC03F, 0xC0C0, 0xC0C3, 0xC0CC, 0xC0CF, 0xC0F0, 0xC0F3, 0xC0FC, 0xC0FF,
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0xC300, 0xC303, 0xC30C, 0xC30F, 0xC330, 0xC333, 0xC33C, 0xC33F, 0xC3C0, 0xC3C3, 0xC3CC, 0xC3CF, 0xC3F0, 0xC3F3, 0xC3FC, 0xC3FF,
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0xCC00, 0xCC03, 0xCC0C, 0xCC0F, 0xCC30, 0xCC33, 0xCC3C, 0xCC3F, 0xCCC0, 0xCCC3, 0xCCCC, 0xCCCF, 0xCCF0, 0xCCF3, 0xCCFC, 0xCCFF,
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0xCF00, 0xCF03, 0xCF0C, 0xCF0F, 0xCF30, 0xCF33, 0xCF3C, 0xCF3F, 0xCFC0, 0xCFC3, 0xCFCC, 0xCFCF, 0xCFF0, 0xCFF3, 0xCFFC, 0xCFFF,
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0xF000, 0xF003, 0xF00C, 0xF00F, 0xF030, 0xF033, 0xF03C, 0xF03F, 0xF0C0, 0xF0C3, 0xF0CC, 0xF0CF, 0xF0F0, 0xF0F3, 0xF0FC, 0xF0FF,
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0xF300, 0xF303, 0xF30C, 0xF30F, 0xF330, 0xF333, 0xF33C, 0xF33F, 0xF3C0, 0xF3C3, 0xF3CC, 0xF3CF, 0xF3F0, 0xF3F3, 0xF3FC, 0xF3FF,
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0xFC00, 0xFC03, 0xFC0C, 0xFC0F, 0xFC30, 0xFC33, 0xFC3C, 0xFC3F, 0xFCC0, 0xFCC3, 0xFCCC, 0xFCCF, 0xFCF0, 0xFCF3, 0xFCFC, 0xFCFF,
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0xFF00, 0xFF03, 0xFF0C, 0xFF0F, 0xFF30, 0xFF33, 0xFF3C, 0xFF3F, 0xFFC0, 0xFFC3, 0xFFCC, 0xFFCF, 0xFFF0, 0xFFF3, 0xFFFC, 0xFFFF
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};
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// 4x5 sprites for hex digits 0-F
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constexpr uint8_t gcvLowResFontData[80] = {
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0xF0, 0x90, 0x90, 0x90, 0xF0,
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0x20, 0x60, 0x20, 0x20, 0x70,
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0xF0, 0x10, 0xF0, 0x80, 0xF0,
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0xF0, 0x10, 0xF0, 0x10, 0xF0,
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0x90, 0x90, 0xF0, 0x10, 0x10,
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0xF0, 0x80, 0xF0, 0x10, 0xF0,
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0xF0, 0x80, 0xF0, 0x90, 0xF0,
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0xF0, 0x10, 0x20, 0x40, 0x40,
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0xF0, 0x90, 0xF0, 0x90, 0xF0,
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0xF0, 0x90, 0xF0, 0x10, 0xF0,
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0xF0, 0x90, 0xF0, 0x90, 0x90,
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0xE0, 0x90, 0xE0, 0x90, 0xE0,
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0xF0, 0x80, 0x80, 0x80, 0xF0,
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0xE0, 0x90, 0x90, 0x90, 0xE0,
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0xF0, 0x80, 0xF0, 0x80, 0xF0,
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0xF0, 0x80, 0xF0, 0x80, 0x80
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};
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Interpreter::Interpreter(Display &display, Buzzer &buzzer, Keypad &keypad, CountdownTimer &delayTimer, CountdownTimer &soundTimer):
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mvMemory(scMemorySize),
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mCallStack{},
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mrDisplay{display},
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mrBuzzer{buzzer},
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mrKeypad{keypad},
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mrDelayTimer(delayTimer),
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mrSoundTimer(soundTimer),
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mvSpecialReg{},
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mvReg{},
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mIsHighResMode{false} {
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// Font sprite data goes into the interpreter reserved memory area
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memcpy(mvMemory.data() + scLowRestFontAddr, gcvLowResFontData, sizeof(gcvLowResFontData));
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// Initialize any non-zero registers at startup
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mvSpecialReg[SR_PC] = scResetVector;
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}
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void Interpreter::tick() {
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// decodes all possible machine code arithmetic opcodes
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constexpr Opcode opcodeMap[16] = {
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Opcode::SET, Opcode::OR, Opcode::AND, Opcode::XOR,
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Opcode::ADD, Opcode::SUB, Opcode::RSH, Opcode::SUB2,
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Opcode::UNIMPL, Opcode::UNIMPL, Opcode::UNIMPL, Opcode::UNIMPL,
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Opcode::UNIMPL, Opcode::UNIMPL, Opcode::LSH, Opcode::UNIMPL,
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};
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// fetch instruction
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sreg_t iInstAddr = mvSpecialReg[SR_PC];
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unsigned inst = (mvMemory.at(iInstAddr) << 8) | mvMemory.at(iInstAddr + 1);
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// increment program counter
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mvSpecialReg[SR_PC] += 2;
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// extract fields
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unsigned iRegDst = (inst & 0x0F00) >> 8; // destination register index
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unsigned iRegSrc = (inst & 0x00F0) >> 4; // source register index
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unsigned opcode = (inst & 0x000F); // arithmetic opcode or sprite index
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unsigned imm8 = (inst & 0x00FF); // 8-bit immediate
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unsigned imm12 = (inst & 0x0FFF); // 12-bit immediate
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switch(inst & 0xF000) {
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case 0x0000: // 0NNN - call machine language routine
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switch(inst) {
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case 0x00E0: // clear display
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mrDisplay.clear();
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break;
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case 0x00EE: // return from subroutine
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mvSpecialReg[SR_PC] = mCallStack.top();
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mCallStack.pop();
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break;
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default:
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throw std::invalid_argument("not implemented");
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break;
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}
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break;
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case 0x1000: // 1NNN - unconditional jump
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mvSpecialReg[SR_PC] = imm12;
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break;
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case 0x2000: // 2NNN - call subroutine
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mCallStack.push(mvSpecialReg[SR_PC]);
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mvSpecialReg[SR_PC] = imm12;
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break;
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case 0x3000: // 3XNN - skip if equal immediate
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executeArithmetic(Opcode::JEQ, iRegDst, imm8);
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break;
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case 0x4000: // 4XNN - skip if nonequal immediate
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executeArithmetic(Opcode::JNEQ, iRegDst, imm8);
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break;
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case 0x5000: // 5XY0 - skip if equal
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executeArithmetic(Opcode::JEQ, iRegDst, mvReg[iRegSrc]);
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break;
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case 0x6000: // 6XNN - load immediate
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executeArithmetic(Opcode::SET, iRegDst, imm8);
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break;
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case 0x7000: // 7XNN - increment
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executeArithmetic(Opcode::ADD, iRegDst, imm8);
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break;
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case 0x8000: // 8XNN - general arithmetic
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executeArithmetic(opcodeMap[opcode], iRegDst, mvReg[iRegSrc]);
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break;
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case 0x9000: // 9XY0 - skip if nonequal
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executeArithmetic(Opcode::JNEQ, iRegDst, mvReg[iRegSrc]);
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break;
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case 0xA000: // ANNN - load I
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mvSpecialReg[SR_I] = imm12;
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break;
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case 0xB000: // BNNN - jump indirect
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mvSpecialReg[SR_I] = mvReg[R_V0] + imm12;
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break;
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case 0xC000: // CXNN - load random
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executeArithmetic(Opcode::RAND, iRegDst, imm8);
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break;
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case 0xD000: // DXYN - draw
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executeDraw(mvReg[iRegDst], mvReg[iRegSrc], opcode);
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break;
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case 0xE000: // EX9E, EXA1 - keypad access
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break;
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case 0xF000: // several unique instructions
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switch(inst & 0xF0FF) {
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case 0xF007: // FX07 - read timer register
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mvReg[iRegDst] = mrDelayTimer.get();
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break;
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case 0xF015: // FX15 - set timer register
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mrDelayTimer.set(mvReg[iRegDst]);
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break;
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case 0xF018: // FX18 - set sound timer register
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if(mvReg[iRegDst] != 0) {
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mrBuzzer.on();
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}
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mrSoundTimer.set(mvReg[iRegDst]);
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break;
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case 0xF01E: // FX1E - add to I
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mvSpecialReg[SR_I] += mvReg[iRegDst];
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break;
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case 0xF029: // FX29 - set I to address of font sprite data for digit X
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mvSpecialReg[SR_I] = scLowRestFontAddr + 5 * mvReg[iRegDst];
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break;
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case 0xF033: // FX33 - convert to bcd
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mvMemory.at(mvSpecialReg[SR_I]) = (mvReg[iRegDst] / 100) % 10;
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mvMemory.at(mvSpecialReg[SR_I] + 1) = (mvReg[iRegDst] / 10) % 10;
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mvMemory.at(mvSpecialReg[SR_I] + 2) = mvReg[iRegDst] % 10;
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break;
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case 0xF055: // FX55 - dump registers
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for(int i = 0; i <= iRegDst - R_V0; i++) {
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mvMemory.at(mvSpecialReg[SR_I]++) = mvReg[R_V0 + i];
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}
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break;
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case 0xF065: // FX65 - restore registers
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for(int i = 0; i <= iRegDst - R_V0; i++) {
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mvReg[R_V0 + i] = mvMemory.at(mvSpecialReg[SR_I]++);
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}
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break;
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default:
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throw std::invalid_argument("not implemented");
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break;
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}
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break;
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}
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if(mrSoundTimer.get() == 0) {
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mrBuzzer.off();
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}
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}
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void Interpreter::loadProgram(char const* data, size_t count, size_t where) {
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if(where + count > scMemorySize) {
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throw std::out_of_range("program exceeds memory bounds or capacity");
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}
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memcpy(mvMemory.data() + where, data, count);
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}
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void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
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reg_t tmp;
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switch(opcode) {
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case Opcode::SET: mvReg[iReg] = operand; break;
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case Opcode::AND: mvReg[iReg] &= operand; break;
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case Opcode::OR: mvReg[iReg] |= operand; break;
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case Opcode::XOR: mvReg[iReg] ^= operand; break;
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case Opcode::RAND: mvReg[iReg] = rand() & operand; break;
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case Opcode::LSH:
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mvReg[iReg] = operand << 1;
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// VF = shifted out bit
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mvReg[R_VF] = (operand & 0x80) ? 1 : 0;
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break;
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case Opcode::RSH:
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mvReg[iReg] = operand >> 1;
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// VF = shifted out bit
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mvReg[R_VF] = (operand & 0x01) ? 1 : 0;
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break;
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case Opcode::ADD:
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mvReg[iReg] = mvReg[iReg] + operand;
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// VF = 1 if carry occurs, VF = 0 if no carry
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mvReg[R_VF] = (mvReg[iReg] < operand) ? 1 : 0;
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break;
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case Opcode::SUB:
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tmp = mvReg[iReg];
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mvReg[iReg] = mvReg[iReg] - operand;
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// VF = 0 if borrow occurs, VF = 1 if no borrow
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mvReg[R_VF] = (mvReg[iReg] > tmp) ? 0 : 1;
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break;
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case Opcode::SUB2:
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mvReg[iReg] = operand - mvReg[iReg];
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// VF = 0 if borrow occurs, VF = 1 if no borrow
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mvReg[R_VF] = (mvReg[iReg] > operand) ? 0 : 1;
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break;
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case Opcode::JEQ:
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if(mvReg[iReg] == operand) {
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mvSpecialReg[SR_PC] += 2;
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}
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break;
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case Opcode::JNEQ:
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if(mvReg[iReg] != operand) {
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mvSpecialReg[SR_PC] += 2;
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}
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break;
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case Opcode::UNIMPL:
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throw std::invalid_argument("invalid opcode");
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break;
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}
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}
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void Interpreter::executeDraw(uint8_t x, uint8_t y, uint8_t n) {
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size_t iMemAddr = mvSpecialReg[SR_I]; // address of the sprite data in memory
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int collisionCount = 0; // number of scanlines in which any pixel changes from on to off
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// coordinates are doubled in low resolution mode
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if(!mIsHighResMode) {
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x *= 2;
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y *= 2;
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}
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x %= gcWidth;
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y %= gcHeight;
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// make x=0 be the right side of the screen instead of the left
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x = gcWidth - x;
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// draw each row of the sprite
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for(int i = 0; i < (mIsHighResMode && n == 0 ? 16 : n); i++) {
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uint16_t spriteRowBits;
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if(mIsHighResMode) {
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// draws an 8xN sprite
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spriteRowBits = mvMemory.at(iMemAddr++) << 8;
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if(n == 0) {
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// draws an 16xN sprite, so fetch another byte from sprite data
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spriteRowBits |= mvMemory.at(iMemAddr++);
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}
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} else {
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// in low-res mode, each sprite pixel draws two on-screen pixels
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spriteRowBits = gcvLowResToHighResRowLookupTable[mvMemory.at(iMemAddr++)];
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}
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// convert to bitset and shift into absolute horizontal position on the screen
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Scanline spriteScanline(spriteRowBits);
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if(x < 16) {
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spriteScanline >>= (16 - x);
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} else {
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spriteScanline <<= (x - 16);
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}
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// we draw one scanline per sprite row in high-res mode, but twice in low-res mode
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for(int j = 0; j < (mIsHighResMode ? 1 : 2); j++) {
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// blit the sprite bitset into the screen
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if(mrDisplay.blit(spriteScanline, y + i * (mIsHighResMode ? 1 : 2) + j) != 0) {
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collisionCount += 1;
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}
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}
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// update state flags
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if(mIsHighResMode) {
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mvReg[R_VF] = collisionCount;
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} else {
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mvReg[R_VF] = (collisionCount > 0 ? 1 : 0);
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}
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}
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}
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}; // namespace chochochip8
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