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Introduce a colour burst.

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This commit is contained in:
Thomas Harte
2025-09-15 23:32:20 -04:00
parent c350f6fe5e
commit 6a91c89126
1 changed files with 10 additions and 41 deletions
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51
Machines/Acorn/BBCMicro/BBCMicro.cpp
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@@ -163,18 +163,14 @@ public:
void perform_bus_cycle(const Motorola::CRTC::BusState &state) {
system_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(state.vsync);
// // The gate array waits 2us to react to the CRTC's vsync signal, and then
// // caps output at 4us. Since the clock rate is 1Mhz, that's 2 and 4 cycles,
// // respectively.
// if(state.hsync) {
// cycles_into_hsync_++;
// } else {
// cycles_into_hsync_ = 0;
// }
//
// const bool is_hsync = (cycles_into_hsync_ >= 2 && cycles_into_hsync_ < 6);
// const bool is_colour_burst = (cycles_into_hsync_ >= 7 && cycles_into_hsync_ < 11);
//
// Count cycles since horizontal sync to insert a colour burst.
if(state.hsync) {
++cycles_into_hsync_;
} else {
cycles_into_hsync_ = 0;
}
const bool is_colour_burst = (cycles_into_hsync_ >= 5 && cycles_into_hsync_ < 9);
// Sync is taken to override pixels, and is combined as a simple OR.
const bool is_sync = state.hsync || state.vsync;
const bool is_blank = !is_sync && state.hsync;
@@ -182,8 +178,8 @@ public:
OutputMode output_mode;
if(is_sync) {
output_mode = OutputMode::Sync;
// } else if(is_colour_burst) {
// output_mode = OutputMode::ColourBurst;
} else if(is_colour_burst) {
output_mode = OutputMode::ColourBurst;
} else if(is_blank) {
output_mode = OutputMode::Blank;
} else if(state.display_enable) {
@@ -275,31 +271,6 @@ public:
// }
// }
// }
//
// // Latch mode four cycles after HSYNC was signalled, if still active.
// if(cycles_into_hsync_ == 4 && mode_ != next_mode_) {
// mode_ = next_mode_;
// switch(mode_) {
// default:
// case 0: pixel_divider_ = 4; break;
// case 1: pixel_divider_ = 2; break;
// case 2: pixel_divider_ = 1; break;
// }
// build_mode_table();
// }
//
// // For the interrupt timer: notify the leading edge of vertical sync and the
// // trailing edge of horizontal sync.
// if(was_vsync_ != state.vsync) {
// interrupt_timer_.set_vsync(state.vsync);
// }
// if(was_hsync_ && !state.hsync) {
// interrupt_timer_.signal_hsync();
// }
//
// // Update current state for edge detection next time around.
// was_vsync_ = state.vsync;
// was_hsync_ = state.hsync;
}
/// Sets the destination for output.
@@ -332,8 +303,6 @@ private:
Pixels
} previous_output_mode_ = OutputMode::Sync;
int cycles_ = 0;
bool was_hsync_ = false, was_vsync_ = false;
int cycles_into_hsync_ = 0;
Outputs::CRT::CRT crt_;