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https://github.com/SourMesen/Mesen.git
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119 lines
2.5 KiB
C++
119 lines
2.5 KiB
C++
#pragma once
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#include "stdafx.h"
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#include "Snapshotable.h"
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//SST39SF040 chip emulation - used by mapper 30 (UNROM512) & mapper 111 (GTROM)
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class FlashSST39SF040 : public Snapshotable
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{
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private:
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enum class ChipMode
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{
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WaitingForCommand,
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Write,
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Erase
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};
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ChipMode _mode = ChipMode::WaitingForCommand;
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uint8_t _cycle = 0;
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uint8_t _softwareId = false;
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//PRG data and size
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uint8_t* _data;
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uint32_t _size;
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protected:
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void StreamState(bool saving)
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{
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Stream(_mode, _cycle, _softwareId);
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}
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public:
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FlashSST39SF040(uint8_t* data, uint32_t size)
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{
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_data = data;
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_size = size;
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}
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int16_t Read(uint32_t addr)
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{
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if(_softwareId) {
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switch(addr & 0x1FF) {
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case 0x00: return 0xBF;
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case 0x01: return 0xB7;
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default: return 0xFF;
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}
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}
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return -1;
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}
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void ResetState()
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{
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_mode = ChipMode::WaitingForCommand;
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_cycle = 0;
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}
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void Write(uint32_t addr, uint8_t value)
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{
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uint16_t cmd = addr & 0x7FFF;
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if(_mode == ChipMode::WaitingForCommand) {
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if(_cycle == 0) {
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if(cmd == 0x5555 && value == 0xAA) {
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//1st write, $5555 = $AA
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_cycle++;
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} else if(value == 0xF0) {
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//Software ID exit
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ResetState();
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_softwareId = false;
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}
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} else if(_cycle == 1 && cmd == 0x2AAA && value == 0x55) {
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//2nd write, $2AAA = $55
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_cycle++;
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} else if(_cycle == 2 && cmd == 0x5555) {
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//3rd write, determines command type
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_cycle++;
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switch(value) {
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case 0x80: _mode = ChipMode::Erase; break;
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case 0x90: ResetState(); _softwareId = true; break;
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case 0xA0: _mode = ChipMode::Write; break;
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case 0xF0: ResetState(); _softwareId = false; break;
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}
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} else {
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_cycle = 0;
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}
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} else if(_mode == ChipMode::Write) {
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//Write a single byte
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if(addr < _size) {
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_data[addr] &= value;
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}
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ResetState();
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} else if(_mode == ChipMode::Erase) {
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if(_cycle == 3) {
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//4th write for erase command, $5555 = $AA
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if(cmd == 0x5555 && value == 0xAA) {
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_cycle++;
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} else {
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ResetState();
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}
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} else if(_cycle == 4) {
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//5th write for erase command, $2AAA = $55
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if(cmd == 0x2AAA && value == 0x55) {
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_cycle++;
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} else {
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ResetState();
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}
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} else if(_cycle == 5) {
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if(cmd == 0x5555 && value == 0x10) {
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//Chip erase
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memset(_data, 0xFF, _size);
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} else if(value == 0x30) {
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//Sector erase
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uint32_t offset = (addr & 0x7F000);
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if(offset + 0x1000 <= _size) {
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memset(_data + offset, 0xFF, 0x1000);
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}
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}
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ResetState();
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}
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}
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}
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}; |