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Add teletext pixel route, albeit without proper selection.

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This commit is contained in:
Thomas Harte
2025-09-24 20:33:07 -04:00
parent 174c8dafbf
commit 2e49bc2044
1 changed files with 22 additions and 12 deletions
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Machines/Acorn/BBCMicro/BBCMicro.cpp
+22 -12
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@@ -319,6 +319,11 @@ public:
bus state and determines what output to produce based on the current palette and mode.
*/
void perform_bus_cycle(const Motorola::CRTC::BusState &state) {
static constexpr size_t PixelAllocationUnit = 480; // Is assumed to be a multiple of both 12 and 16.
// i.e. a multiple of 48.
static_assert(!(PixelAllocationUnit % 16));
static_assert(!(PixelAllocationUnit % 12));
system_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(state.vsync);
// Count cycles since horizontal sync to insert a colour burst.
@@ -382,14 +387,14 @@ public:
// 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.
if(pixel_data_ && (pixels_collected() == 320 || active_collation_ != previous_collation_)) {
if(pixel_data_ && (pixels_collected() == PixelAllocationUnit || active_collation_ != previous_collation_)) {
flush_pixels();
cycles_ = 0;
}
previous_collation_ = active_collation_;
if(!pixel_data_) {
pixel_pointer_ = pixel_data_ = crt_.begin_data(320, 8);
pixel_pointer_ = pixel_data_ = crt_.begin_data(PixelAllocationUnit, 8);
}
if(pixel_pointer_) {
uint16_t address;
@@ -409,17 +414,22 @@ public:
}
}
// Hard coded: pixel mode! TODO: teletext mode.
pixel_shifter_ = should_fetch ? ram_[address] : 0;
// pixel_shifter_ = should_fetch ? (address & 0xff) : 0; // TODO: eliminate once 6845 addresses are
// meaningful again.
switch(crtc_clock_multiplier_ * active_collation_.pixels_per_clock) {
case 1: shift_pixels<1>(cursor_shifter_ & 7); break;
case 2: shift_pixels<2>(cursor_shifter_ & 7); break;
case 4: shift_pixels<4>(cursor_shifter_ & 7); break;
case 8: shift_pixels<8>(cursor_shifter_ & 7); break;
case 16: shift_pixels<16>(cursor_shifter_ & 7); break;
default: break;
if(active_collation_.is_teletext) {
// TODO: output meaningful teletext pixels.
for(int c = 0; c < 12; c++) {
*pixel_pointer_++ = (pixel_shifter_ & 0x80 ? 0xff : 0x00) ^ cursor_mask_;
pixel_shifter_ <<= 1;
}
} else {
switch(crtc_clock_multiplier_ * active_collation_.pixels_per_clock) {
case 1: shift_pixels<1>(cursor_shifter_ & 7); break;
case 2: shift_pixels<2>(cursor_shifter_ & 7); break;
case 4: shift_pixels<4>(cursor_shifter_ & 7); break;
case 8: shift_pixels<8>(cursor_shifter_ & 7); break;
case 16: shift_pixels<16>(cursor_shifter_ & 7); break;
default: break;
}
}
}
}