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Attempt to distinguish clocks.

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This commit is contained in:
Thomas Harte 2023-12-06 10:41:20 -05:00
parent c5aa3fc75c
commit bf49f745bf
1 changed files with 41 additions and 37 deletions
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78
Machines/PCCompatible/CGA.hpp
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@ -98,15 +98,11 @@ class CGA {
if(control & 0x2) {
mode_ = (control & 0x10) ? Mode::Pixels640 : Mode::Pixels320;
pixels_per_tick = (mode_ == Mode::Pixels640) ? 16 : 8;
} else {
mode_ = Mode::Text;
pixels_per_tick = 8;
}
// TODO: I think I need a separate clock divider, which affects the input to the CRTC,
// and an output multiplier, to set how many pixels are generated per CRTC tick.
//
// 640px mode generates 16 pixels per tick, all the other modes generate 8.
// The clock is divided by 1 in all 80-column text mode, 2 in all other modes.
clock_divider = 1 + !(control & 0x01);
}
@ -121,19 +117,20 @@ class CGA {
((state.display_enable && control_&0x08) ? OutputState::Pixels : OutputState::Border);
// Upon either a state change or just having accumulated too much local time...
if(new_state != output_state || pixels_divider != clock_divider || count > 912) {
if(new_state != output_state || active_pixels_per_tick != pixels_per_tick || active_clock_divider != clock_divider || count > 912) {
// (1) flush preexisting state.
if(count) {
switch(output_state) {
case OutputState::Sync: crt.output_sync(count * clock_divider); break;
case OutputState::Border: crt.output_blank(count * clock_divider); break;
case OutputState::Pixels: flush_pixels(); break;
case OutputState::Sync: crt.output_sync(count * active_clock_divider); break;
case OutputState::Border: crt.output_blank(count * active_clock_divider); break;
case OutputState::Pixels: flush_pixels(); break;
}
}
// (2) adopt new state.
output_state = new_state;
pixels_divider = clock_divider;
active_pixels_per_tick = pixels_per_tick;
active_clock_divider = clock_divider;
count = 0;
}
@ -144,16 +141,14 @@ class CGA {
// Flush any period where pixels weren't recorded due to back pressure.
if(pixels && count) {
crt.output_blank(count * clock_divider);
crt.output_blank(count * active_clock_divider);
count = 0;
}
}
if(pixels) {
if(state.cursor) {
pixel_pointer[0] = pixel_pointer[1] = pixel_pointer[2] = pixel_pointer[3] =
pixel_pointer[4] = pixel_pointer[5] = pixel_pointer[6] = pixel_pointer[7] =
pixel_pointer[8] = 0x3f; // i.e. white.
std::fill(pixel_pointer, pixel_pointer + pixels_per_tick, 0x3f); // i.e. white.
} else {
if(mode_ == Mode::Text) {
serialise_text(state);
@ -161,7 +156,7 @@ class CGA {
serialise_pixels(state);
}
}
pixel_pointer += 8;
pixel_pointer += pixels_per_tick;
}
}
@ -177,7 +172,7 @@ class CGA {
void perform_bus_cycle_phase2(const Motorola::CRTC::BusState &) {}
void flush_pixels() {
crt.output_data(count * pixels_divider, size_t(count));
crt.output_data(count * active_clock_divider, size_t(count));
pixels = pixel_pointer = nullptr;
}
@ -188,18 +183,21 @@ class CGA {
// character code + attributes except that these are two bytes worth of graphics.
//
// Meanwhile, row address is used to invent a 15th address line.
const uint8_t bitmap = ram[((state.refresh_address << 1) + (state.row_address << 13)) & 0x3fff];
// const uint8_t bitmap = ram[(state.refresh_address + (state.row_address << 13)) & 0x3fff];
const auto base_address = ((state.refresh_address << 1) + (state.row_address << 13)) & 0x3fff;
const uint8_t bitmap[] = {
ram[base_address],
ram[base_address + 1],
};
// Better than nothing...
pixel_pointer[0] =
pixel_pointer[1] = (bitmap & 0xc0) >> 6;
pixel_pointer[2] =
pixel_pointer[3] = (bitmap & 0x30) >> 4;
pixel_pointer[4] =
pixel_pointer[5] = (bitmap & 0x0c) >> 2;
pixel_pointer[6] =
pixel_pointer[7] = (bitmap & 0x03) >> 0;
pixel_pointer[0] = (bitmap[0] & 0xc0) >> 6;
pixel_pointer[1] = (bitmap[0] & 0x30) >> 4;
pixel_pointer[2] = (bitmap[0] & 0x0c) >> 2;
pixel_pointer[3] = (bitmap[0] & 0x03) >> 0;
pixel_pointer[4] = (bitmap[1] & 0xc0) >> 6;
pixel_pointer[5] = (bitmap[1] & 0x30) >> 4;
pixel_pointer[6] = (bitmap[1] & 0x0c) >> 2;
pixel_pointer[7] = (bitmap[1] & 0x03) >> 0;
}
void serialise_text(const Motorola::CRTC::BusState &state) {
@ -240,26 +238,32 @@ class CGA {
}
Outputs::CRT::CRT crt;
static constexpr size_t DefaultAllocationSize = 320;
// Current output stream.
uint8_t *pixels = nullptr;
uint8_t *pixel_pointer = nullptr;
int active_pixels_per_tick = 8;
int active_clock_divider = 1;
// Source data.
const uint8_t *ram = nullptr;
std::vector<uint8_t> font;
// CRTC state tracking, for CRT serialisation.
enum class OutputState {
Sync, Pixels, Border
} output_state = OutputState::Sync;
int count = 0;
uint8_t *pixels = nullptr;
uint8_t *pixel_pointer = nullptr;
int pixels_divider = 1;
static constexpr size_t DefaultAllocationSize = 320;
const uint8_t *ram = nullptr;
std::vector<uint8_t> font;
// Current Programmer-set parameters.
int clock_divider = 1;
int pixels_per_tick = 8;
uint8_t control_ = 0;
enum class Mode {
Pixels640, Pixels320, Text,
} mode_ = Mode::Text;
int clock_divider = 1;
} outputter_;
Motorola::CRTC::CRTC6845<CRTCOutputter, Motorola::CRTC::CursorType::MDA> crtc_;