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Adjust factoring of read and write per expanded V9938 scope.

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This commit is contained in:
Thomas Harte 2023-01-18 12:36:57 -05:00
parent 339086d597
commit 355ee7fbc7
2 changed files with 100 additions and 32 deletions
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122
Components/9918/Implementation/9918.cpp
View File

@ -517,21 +517,30 @@ void Base<personality>::output_border(int cycles, [[maybe_unused]] uint32_t cram
}
}
// MARK: - External interface.
template <Personality personality>
void TMS9918<personality>::write(int address, uint8_t value) {
// Writes to address 0 are writes to the video RAM. Store
// the value and return.
if(!(address & 1)) {
this->write_phase_ = false;
// Enqueue the write to occur at the next available slot.
this->read_ahead_buffer_ = value;
this->queued_access_ = MemoryAccess::Write;
this->cycles_until_access_ = Timing<personality>::VRAMAccessDelay;
return;
int Base<personality>::masked_address(int address) {
if constexpr (is_yamaha_vdp(personality)) {
return address & 3;
} else {
return address & 1;
}
}
template <Personality personality>
void Base<personality>::write_vram(uint8_t value) {
// Latch the value and exit.
this->write_phase_ = false;
// Enqueue the write to occur at the next available slot.
this->read_ahead_buffer_ = value;
this->queued_access_ = MemoryAccess::Write;
this->cycles_until_access_ = Timing<personality>::VRAMAccessDelay;
}
template <Personality personality>
void Base<personality>::write_register(uint8_t value) {
// Writes to address 1 are performed in pairs; if this is the
// low byte of a value, store it and wait for the high byte.
if(!this->write_phase_) {
@ -648,6 +657,75 @@ void TMS9918<personality>::write(int address, uint8_t value) {
}
}
template <Personality personality>
void Base<personality>::write_palette(uint8_t value) {
LOG("Palette write TODO");
(void)value;
}
template <Personality personality>
void Base<personality>::write_register_indirect(uint8_t value) {
LOG("Register indirect write TODO");
(void)value;
}
template <Personality personality>
void TMS9918<personality>::write(int address, uint8_t value) {
switch(this->masked_address(address)) {
default: break;
case 0: this->write_vram(value); break;
case 1: this->write_register(value); break;
case 2: this->write_palette(value); break;
case 3: this->write_register_indirect(value); break;
}
}
template <Personality personality>
uint8_t Base<personality>::read_vram() {
// Take whatever is currently in the read-ahead buffer and
// enqueue a further read to occur at the next available slot.
const uint8_t result = this->read_ahead_buffer_;
this->queued_access_ = MemoryAccess::Read;
return result;
}
template <Personality personality>
uint8_t Base<personality>::read_register() {
// Gets the status register.
const uint8_t result = this->status_;
this->status_ &= ~(StatusInterrupt | StatusSpriteOverflow | StatusSpriteCollision);
this->line_interrupt_pending_ = false;
return result;
}
template <Personality personality>
uint8_t Base<personality>::read_palette() {
LOG("Palette read TODO");
return 0xff;
}
template <Personality personality>
uint8_t Base<personality>::read_register_indirect() {
LOG("Register indirect read TODO");
return 0xff;
}
template <Personality personality>
uint8_t TMS9918<personality>::read(int address) {
// TODO: is this still a global effect of reads, even in the world of the Yamahas?
this->write_phase_ = false;
switch(this->masked_address(address)) {
default: return 0xff;
case 0: return this->read_vram();
case 1: return this->read_register();
case 2: return this->read_palette();
case 3: return this->read_register_indirect();
}
}
// MARK: - Ephemeral state.
template <Personality personality>
uint8_t TMS9918<personality>::get_current_line() const {
// Determine the row to return.
@ -682,26 +760,6 @@ uint8_t TMS9918<personality>::get_current_line() const {
return uint8_t(source_row);
}
template <Personality personality>
uint8_t TMS9918<personality>::read(int address) {
this->write_phase_ = false;
// Reads from address 0 read video RAM, via the read-ahead buffer.
if(!(address & 1)) {
// Enqueue the write to occur at the next available slot.
const uint8_t result = this->read_ahead_buffer_;
this->queued_access_ = MemoryAccess::Read;
return result;
}
// Reads from address 1 get the status register.
const uint8_t result = this->status_;
this->status_ &= ~(StatusInterrupt | StatusSpriteOverflow | StatusSpriteCollision);
this->line_interrupt_pending_ = false;
return result;
}
template <Personality personality>
HalfCycles TMS9918<personality>::get_next_sequence_point() const {
if(!this->generate_interrupts_ && !this->enable_line_interrupts_) return HalfCycles::max();

10
Components/9918/Implementation/9918Base.hpp
View File

@ -286,6 +286,16 @@ template <Personality personality> struct Base {
size_t sprite_generator_table_address;
} master_system_;
int masked_address(int address);
void write_vram(uint8_t);
void write_register(uint8_t);
void write_palette(uint8_t);
void write_register_indirect(uint8_t);
uint8_t read_vram();
uint8_t read_register();
uint8_t read_palette();
uint8_t read_register_indirect();
ScreenMode current_screen_mode() const {
if(blank_display_) {
return ScreenMode::Blank;