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Rejig to ensure SAA output ends.

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This commit is contained in:
Thomas Harte
2025-09-25 21:31:21 -04:00
parent 26ccd930c3
commit f8c11bf217
1 changed files with 60 additions and 60 deletions
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120
Machines/Acorn/BBCMicro/BBCMicro.cpp
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@@ -325,12 +325,12 @@ public:
// Count cycles since horizontal sync to insert a colour burst.
// TODO: this is copy/pasted from the CPC. How does the BBC do it?
if(state.hsync) {
++cycles_into_hsync_;
} else {
cycles_into_hsync_ = 0;
}
const bool is_colour_burst = cycles_into_hsync_ >= 5 && cycles_into_hsync_ < 9;
// if(state.hsync) {
// ++cycles_into_hsync_;
// } else {
// cycles_into_hsync_ = 0;
// }
// const bool is_colour_burst = cycles_into_hsync_ >= 5 && cycles_into_hsync_ < 9;
// Check for a cursor leading edge.
cursor_shifter_ >>= 4;
@@ -344,20 +344,6 @@ public:
previous_cursor_enabled_ = state.cursor;
}
const bool should_fetch = state.display_enable && (active_collation_.is_teletext || !(state.line.get() & 8));
const OutputMode output_mode = [&] {
if(state.hsync || state.vsync) {
return OutputMode::Sync;
}
if(is_colour_burst) {
return OutputMode::ColourBurst;;
}
if(should_fetch || cursor_shifter_ || (active_collation_.is_teletext && saa5050_serialiser_.has_output())) {
return OutputMode::Pixels;
}
return OutputMode::Blank;
} ();
// Consider some SAA5050 signalling.
if(!state.vsync && previous_vsync_) {
// Complete fiction here; the SAA5050 field flag is set by peeking inside CRTC state.
@@ -371,6 +357,52 @@ public:
}
previous_display_enabled_ = state.display_enable;
// Grab 5050 output, if any.
bool has_5050_output_ = saa5050_serialiser_.has_output();
const auto saa_50505_output_ = saa5050_serialiser_.output();
// Fetch, possibly.
const bool should_fetch = state.display_enable && (active_collation_.is_teletext || !(state.line.get() & 8));
if(should_fetch) {
const uint16_t address = [&] {
// Teletext address generation.
if(state.refresh.get() & (1 << 13)) {
return uint16_t(
0x3c00 |
((state.refresh.get() & 0x800) << 3) |
(state.refresh.get() & 0x3ff)
);
}
uint16_t address = uint16_t((state.refresh.get() << 3) | (state.line.get() & 7));
if(address & 0x8000) {
address = (address + video_base_) & 0x7fff;
}
return address;
} ();
const uint8_t fetched = ram_[address];
pixel_shifter_ = fetched;
saa5050_serialiser_.add(fetched);
}
// Pick new output mode.
const OutputMode output_mode = [&] {
if(state.hsync || state.vsync) {
return OutputMode::Sync;
}
// if(is_colour_burst) {
// return OutputMode::ColourBurst;
// }
if(
(should_fetch && !active_collation_.is_teletext) ||
(has_5050_output_ && active_collation_.is_teletext) ||
cursor_shifter_
) {
return OutputMode::Pixels;
}
return OutputMode::Blank;
} ();
// If a transition between sync/border/pixels just occurred, flush whatever was
// in progress to the CRT and reset counting. Also flush if this mode has just been effective
// for a really long time, so as not to buffer too much.
@@ -389,11 +421,8 @@ public:
previous_output_mode_ = output_mode;
}
// Increment cycles since state changed.
cycles_ += crtc_clock_multiplier_ << 3;
// Collect some more pixels if output is ongoing.
if(previous_output_mode_ == OutputMode::Pixels) {
if(output_mode == OutputMode::Pixels) {
// Flush the current buffer pixel if full; the CRTC allows many different display
// widths so it's not necessarily possible to predict the correct number in advance
// and using the upper bound could lead to inefficient behaviour.
@@ -407,34 +436,13 @@ public:
pixel_pointer_ = pixel_data_ = crt_.begin_data(PixelAllocationUnit, 8);
}
const uint16_t address = [&] {
// Teletext address generation.
if(state.refresh.get() & (1 << 13)) {
return uint16_t(
0x3c00 |
((state.refresh.get() & 0x800) << 3) |
(state.refresh.get() & 0x3ff)
);
}
uint16_t address = uint16_t((state.refresh.get() << 3) | (state.line.get() & 7));
if(address & 0x8000) {
address = (address + video_base_) & 0x7fff;
}
return address;
} ();
const uint8_t fetched = should_fetch ? ram_[address] : 0;
pixel_shifter_ = fetched;
if(pixel_data_) {
if(active_collation_.is_teletext) {
if(saa5050_serialiser_.has_output()) {
const auto output = saa5050_serialiser_.output();
uint16_t pixels = output.pixels;
if(has_5050_output_) {
uint16_t pixels = saa_50505_output_.pixels;
for(int c = 0; c < 12; c++) {
*pixel_pointer_++ =
((pixels & 0b1000'0000'0000) ? output.alpha : output.background)
((pixels & 0b1000'0000'0000) ? saa_50505_output_.alpha : saa_50505_output_.background)
^ uint8_t(cursor_shifter_);
pixels <<= 1;
}
@@ -452,19 +460,11 @@ public:
default: break;
}
}
} /*else {
if(active_collation_.is_teletext) {
pixel_pointer_ += 12;
} else {
pixel_pointer_ += crtc_clock_multiplier_ * active_collation_.pixels_per_clock;
}
} */
// TODO: why does enabling the below cause alternate lines to be different stretches?
// if(should_fetch) {
saa5050_serialiser_.add(fetched);
// }
}
}
// Increment cycles since state changed.
cycles_ += crtc_clock_multiplier_ << 3;
}
/// Sets the destination for output.