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Improve state guesswork.
This commit is contained in:
Thomas Harte
parent
ec73c00c3b
commit
6123350895
@ -130,14 +130,11 @@ struct Video {
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// Pick new horizontal state, possibly rolling over into the vertical.
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horizontal_state_.increment_position(horizontal_timing_);
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if(horizontal_state_.position == horizontal_timing_.period) {
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horizontal_state_.position = 0;
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if(horizontal_state_.did_restart()) {
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const auto old_phase = vertical_state_.phase();
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vertical_state_.increment_position(vertical_timing_);
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pixel_count_ = 0;
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if(vertical_state_.position == vertical_timing_.period) {
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vertical_state_.position = 0;
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if(vertical_state_.did_restart()) {
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entered_sync_ = true;
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interrupt_observer_.update_interrupts();
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}
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@ -168,6 +165,45 @@ struct Video {
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cursor_pixel_ = 32;
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}
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// Accumulate total phase.
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++time_in_phase_;
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// Determine current output phase.
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Phase new_phase;
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switch(vertical_state_.phase()) {
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case Phase::Sync: new_phase = Phase::Sync; break;
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case Phase::Blank: new_phase = Phase::Blank; break;
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case Phase::Border:
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new_phase = horizontal_state_.phase() == Phase::Display ? Phase::Border : horizontal_state_.phase();
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break;
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case Phase::Display:
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new_phase = horizontal_state_.phase();
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break;
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}
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const auto flush_pixels = [&]() {
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const auto duration = static_cast<int>(time_in_phase_);
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crt_.output_data(duration, static_cast<size_t>(time_in_phase_) * 2);
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time_in_phase_ = 0;
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pixels_ = nullptr;
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};
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// Possibly output something.
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if(new_phase != phase_) {
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if(time_in_phase_) {
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const auto duration = static_cast<int>(time_in_phase_);
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switch(phase_) {
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case Phase::Sync: crt_.output_sync(duration); break;
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case Phase::Blank: crt_.output_blank(duration); break;
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case Phase::Display: flush_pixels(); break;
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case Phase::Border: crt_.output_level<uint16_t>(duration, border_colour_); break;
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}
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time_in_phase_ = 0;
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}
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phase_ = new_phase;
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}
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// Update cursor pixel counter if applicable; this might mean triggering it
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// and it might just mean advancing it if it has already been triggered.
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if(vertical_state_.cursor_active) {
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@ -178,12 +214,39 @@ struct Video {
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}
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// Grab some more pixels if appropriate.
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const auto flush_pixels = [&]() {
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const auto duration = static_cast<int>(time_in_phase_);
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crt_.output_data(duration, static_cast<size_t>(time_in_phase_) * 2);
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time_in_phase_ = 0;
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pixels_ = nullptr;
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};
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if(vertical_state_.display_active() && horizontal_state_.display_active()) {
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const auto next_byte = [&]() -> uint8_t {
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const auto next = ram_[address_];
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++address_;
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// `buffer_end_` is the final address that a 16-byte block will be fetched from;
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// the +16 here papers over the fact that I'm not accurately implementing DMA.
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if(address_ == buffer_end_ + 16) {
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address_ = buffer_start_;
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}
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return next;
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};
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switch(colour_depth_) {
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case Depth::EightBPP:
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pixel_data_[0] = next_byte();
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pixel_data_[1] = next_byte();
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break;
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case Depth::FourBPP:
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pixel_data_[0] = next_byte();
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break;
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case Depth::TwoBPP:
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if(!(pixel_count_&1)) {
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pixel_data_[0] = next_byte();
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}
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break;
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case Depth::OneBPP:
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if(!(pixel_count_&3)) {
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pixel_data_[0] = next_byte();
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}
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break;
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}
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}
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if(phase_ == Phase::Display) {
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if(pixels_ && time_in_phase_ == PixelBufferSize/2) {
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@ -198,17 +261,6 @@ struct Video {
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pixels_ = reinterpret_cast<uint16_t *>(crt_.begin_data(PixelBufferSize));
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}
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const auto next_byte = [&]() -> uint8_t {
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const auto next = ram_[address_];
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++address_;
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// `buffer_end_` is the final address that a 16-byte block will be fetched from;
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// the +16 here papers over the fact that I'm not accurately implementing DMA.
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if(address_ == buffer_end_ + 16) {
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address_ = buffer_start_;
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}
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return next;
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};
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if(pixels_) {
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// Each tick in here is two ticks of the pixel clock, so:
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@ -218,40 +270,27 @@ struct Video {
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// 2bpp mode: output one byte every second tick;
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// 1bpp mode: output one byte every fourth tick.
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switch(colour_depth_) {
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case Depth::EightBPP: {
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uint8_t next = next_byte();
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pixels_[0] = (colours_[next & 0xf] & colour(0b0111'0011'0111)) | high_spread[next >> 4];
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case Depth::EightBPP:
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pixels_[0] = (colours_[pixel_data_[0] & 0xf] & colour(0b0111'0011'0111)) | high_spread[pixel_data_[0] >> 4];
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pixels_[1] = (colours_[pixel_data_[1] & 0xf] & colour(0b0111'0011'0111)) | high_spread[pixel_data_[1] >> 4];
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break;
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next = next_byte();
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pixels_[1] = (colours_[next & 0xf] & colour(0b0111'0011'0111)) | high_spread[next >> 4];
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} break;
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case Depth::FourBPP:
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pixels_[0] = colours_[pixel_data_[0] & 0xf];
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pixels_[1] = colours_[pixel_data_[0] >> 4];
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break;
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case Depth::FourBPP: {
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const uint8_t next = next_byte();
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case Depth::TwoBPP:
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pixels_[0] = colours_[pixel_data_[0] & 3];
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pixels_[1] = colours_[(pixel_data_[0] >> 2) & 3];
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pixel_data_[0] >>= 4;
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break;
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pixels_[0] = colours_[next & 0xf];
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pixels_[1] = colours_[next >> 4];
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} break;
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case Depth::TwoBPP: {
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if(!(pixel_count_&1)) {
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pixel_data_ = next_byte();
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}
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pixels_[0] = colours_[pixel_data_ & 3];
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pixels_[1] = colours_[(pixel_data_ >> 2) & 3];
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pixel_data_ >>= 4;
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} break;
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case Depth::OneBPP: {
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if(!(pixel_count_&3)) {
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pixel_data_ = next_byte();
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}
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pixels_[0] = colours_[pixel_data_ & 1];
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pixels_[1] = colours_[(pixel_data_ >> 1) & 1];
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pixel_data_ >>= 2;
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} break;
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case Depth::OneBPP:
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pixels_[0] = colours_[pixel_data_[0] & 1];
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pixels_[1] = colours_[(pixel_data_[0] >> 1) & 1];
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pixel_data_[0] >>= 2;
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break;
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}
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// Overlay cursor if applicable.
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@ -269,68 +308,16 @@ struct Video {
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pixels_[1] = cursor_colours_[pixel];
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}
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}
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cursor_pixel_ += 2;
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}
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pixels_ += 2;
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} else {
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switch(colour_depth_) {
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case Depth::EightBPP:
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next_byte();
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next_byte();
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break;
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case Depth::FourBPP:
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next_byte();
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break;
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case Depth::TwoBPP:
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if(!(pixel_count_&1)) {
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next_byte();
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}
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break;
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case Depth::OneBPP:
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if(!(pixel_count_&3)) {
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next_byte();
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}
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break;
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}
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}
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++pixel_count_;
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}
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// Accumulate total phase.
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++time_in_phase_;
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// Determine current output phase.
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Phase new_phase;
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switch(vertical_state_.phase()) {
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case Phase::Sync: new_phase = Phase::Sync; break;
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case Phase::Blank: new_phase = Phase::Blank; break;
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case Phase::Border:
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new_phase = horizontal_state_.phase() == Phase::Display ? Phase::Border : horizontal_state_.phase();
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break;
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case Phase::Display:
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new_phase = horizontal_state_.phase();
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break;
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}
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// Possibly output something.
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if(new_phase != phase_) {
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if(time_in_phase_) {
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const auto duration = static_cast<int>(time_in_phase_);
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switch(phase_) {
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case Phase::Sync: crt_.output_sync(duration); break;
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case Phase::Blank: crt_.output_blank(duration); break;
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case Phase::Display: flush_pixels(); break;
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case Phase::Border: crt_.output_level<uint16_t>(duration, border_colour_); break;
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}
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time_in_phase_ = 0;
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}
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phase_ = new_phase;
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}
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}
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// Advance cursor position.
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if(cursor_pixel_ < 32) cursor_pixel_ += 2; }
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/// @returns @c true if a vertical retrace interrupt has been signalled since the last call to @c interrupt(); @c false otherwise.
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bool interrupt() {
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@ -389,36 +376,52 @@ private:
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if(position == 1024) position = 0;
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if(position == timing.period) {
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sync_active = timing.sync_width;
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display_started = !timing.display_start;
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display_ended = !timing.display_end;
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border_started = !timing.border_start;
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border_ended = !timing.border_end;
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cursor_active = !timing.cursor_start;
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} else {
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sync_active &= position != timing.sync_width;
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display_started |= position == timing.display_start;
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display_ended |= position == timing.display_end;
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border_started |= position == timing.border_start;
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border_ended |= position == timing.border_end;
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cursor_active |= position == timing.cursor_start;
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cursor_active &= position != timing.cursor_end;
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state = DidRestart;
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position = 0;
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}
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if(position == timing.sync_width) state |= SyncEnded;
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if(position == timing.display_start) state |= DisplayStarted;
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if(position == timing.display_end) state |= DisplayEnded;
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if(position == timing.border_start) state |= BorderStarted;
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if(position == timing.border_end) state |= BorderEnded;
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cursor_active |= position == timing.cursor_start;
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cursor_active &= position != timing.cursor_end;
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}
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bool sync_active = true;
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bool border_started = false;
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bool border_ended = false;
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bool display_started = false;
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bool display_ended = false;
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static constexpr uint8_t SyncEnded = 0x1;
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static constexpr uint8_t BorderStarted = 0x2;
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static constexpr uint8_t BorderEnded = 0x4;
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static constexpr uint8_t DisplayStarted = 0x8;
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static constexpr uint8_t DisplayEnded = 0x10;
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static constexpr uint8_t DidRestart = 0x20;
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uint8_t state = 0;
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bool cursor_active = false;
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bool did_restart() {
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const bool result = state & DidRestart;
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state &= ~DidRestart;
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return result;
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}
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bool display_active() const {
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return (state & DisplayStarted) && !(state & DisplayEnded);
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}
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Phase phase() const {
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if(sync_active) return Phase::Sync;
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if(display_started && !display_ended) return Phase::Display;
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if(border_started && !border_ended) return Phase::Border;
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return Phase::Blank;
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// TODO: turn the following logic into a 32-entry lookup table.
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if(!(state & SyncEnded)) {
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return Phase::Sync;
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}
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if(!(state & BorderStarted) || (state & BorderEnded)) {
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return Phase::Blank;
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}
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if(!(state & DisplayStarted) || (state & DisplayEnded)) {
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return Phase::Border;
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}
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return Phase::Display;
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}
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};
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State horizontal_state_, vertical_state_;
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@ -445,7 +448,7 @@ private:
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std::array<uint8_t, 32> cursor_image_;
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// Ephemeral graphics data.
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uint8_t pixel_data_ = 0;
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uint8_t pixel_data_[2]{};
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// Colour palette, converted to internal format.
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uint16_t border_colour_;
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