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Edge towards clock-independent line composition.

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This commit is contained in:
Thomas Harte 2023-01-07 14:57:32 -05:00
parent cdf547ac82
commit 72e0bfecc1
2 changed files with 71 additions and 7 deletions
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19
Components/9918/Implementation/9918.cpp
View File

@ -319,9 +319,11 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
int read_cycles = target_read_cycles - read_cycles_performed;
if(!read_cycles) continue;
// Grab the next CRAM dot value and schedule a break in output if applicable.
const uint32_t cram_value = next_cram_value;
next_cram_value = 0;
if constexpr (is_sega_vdp(personality)) {
next_cram_value = 0;
if(!this->upcoming_cram_dots_.empty() && this->upcoming_cram_dots_.front().location.row == this->read_pointer_.row) {
int time_until_dot = this->upcoming_cram_dots_.front().location.column - this->read_pointer_.column;
@ -353,16 +355,21 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
#define border(left, right) intersect(left, right, this->output_border(end - start, cram_value))
// TODO: CRT clock might need to change?
if(line_buffer.line_mode == LineMode::Refresh || this->read_pointer_.row > this->mode_timing_.pixel_lines) {
if(this->read_pointer_.row >= this->mode_timing_.first_vsync_line && this->read_pointer_.row < this->mode_timing_.first_vsync_line+4) {
if(
this->read_pointer_.row >= this->mode_timing_.first_vsync_line &&
this->read_pointer_.row < this->mode_timing_.first_vsync_line + 4
) {
// Vertical sync.
if(end_column == 342) {
this->crt_.output_sync(342 * 4);
// TODO: the Mega Drive supports interlaced video, I think?
if(end_column == Timing<personality>::CyclesPerLine) {
this->crt_.output_sync(
this->clock_converter_.to_crt_clock(Timing<personality>::CyclesPerLine)
);
}
} else {
// Right border.
border(0, 15);
border(0, Timing<personality>::EndOfRightBorder);
// Blanking region; total length is 58 cycles,
// and 58+15 = 73. So output the lot when the

57
Components/9918/Implementation/ClockConverter.hpp
View File

@ -40,24 +40,61 @@ struct Timing<personality, std::enable_if_t<is_classic_vdp(personality)>> {
/// The final internal cycle at which pixels will be output text mode.
constexpr static int LastTextCycle = 334;
// For the below, the fixed portion of line layout is:
//
// [0, EndOfRightBorder): right border colour
// [EndOfRightBorder, StartOfSync): blank
// [StartOfSync, EndOfSync): sync
// [EndOfSync, StartOfColourBurst): blank
// [StartOfColourBurst, EndOfColourBurst): the colour burst
// [EndOfColourBurst, StartOfLeftBorder): blank
//
// The region from StartOfLeftBorder until the end is then filled with
// some combination of pixels and more border, depending on the vertical
// position of this line and the current screen mode.
constexpr static int EndOfRightBorder = 15;
constexpr static int StartOfSync = 23;
constexpr static int EndOfSync = 49;
constexpr static int StartOfColourBurst = 51;
constexpr static int EndOfColourBurst = 65;
constexpr static int StartOfLeftBorder = 73;
};
template <Personality personality>
struct Timing<personality, std::enable_if_t<is_yamaha_vdp(personality)>> {
constexpr static int CyclesPerLine = 1368;
constexpr static int VRAMAccessDelay = 6;
constexpr static int FirstPixelCycle = 344;
constexpr static bool SupportsTextMode = true;
constexpr static int FirstTextCycle = 376;
constexpr static int LastTextCycle = 1336;
constexpr static int EndOfRightBorder = 15 * 4;
constexpr static int StartOfSync = 23 * 4;
constexpr static int EndOfSync = 49 * 4;
constexpr static int StartOfColourBurst = 51 * 4;
constexpr static int EndOfColourBurst = 65 * 4;
constexpr static int StartOfLeftBorder = 73 * 4;
};
template <>
struct Timing<Personality::MDVDP> {
constexpr static int CyclesPerLine = 3420;
constexpr static int VRAMAccessDelay = 6;
constexpr static int FirstPixelCycle = 860;
constexpr static bool SupportsTextMode = false;
// Implementation note: these currently need to be multiples of 2.5
// per the stateless Mega Drive -> CRT clock conversion.
constexpr static int EndOfRightBorder = 15 * 10;
constexpr static int StartOfSync = 23 * 10;
constexpr static int EndOfSync = 49 * 10;
constexpr static int StartOfColourBurst = 51 * 10;
constexpr static int EndOfColourBurst = 65 * 10;
constexpr static int StartOfLeftBorder = 73 * 10;
};
constexpr int TMSAccessWindowsPerLine = 171;
@ -170,6 +207,26 @@ template <Personality personality> class ClockConverter {
}
}
/*!
Convers a position in internal cycles to its corresponding position
on the CRT's output clock, which [TODO] is clocked so that
1368 cycles is 228 NTSC colour cycles.
*/
static constexpr int to_crt_clock(int source) {
switch(personality) {
default:
return source * 4;
case Personality::V9938:
case Personality::V9958:
return source;
case Personality::MDVDP:
return (source * 2) / 5;
}
}
private:
// Holds current residue in conversion from the external to
// internal clock.