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Pulled vertical sync detection entirely outside the loop, and gave it greater perspective.

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This commit is contained in:
Thomas Harte 2017-03-06 19:15:33 -05:00
parent ad73379d1c
commit e63229a5e5
2 changed files with 23 additions and 9 deletions
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27
Outputs/CRT/CRT.cpp
View File

@ -34,9 +34,10 @@ void CRT::set_new_timing(unsigned int cycles_per_line, unsigned int height_of_di
colour_cycle_numerator_ = colour_cycle_numerator;
phase_alternates_ = should_alternate;
is_alernate_line_ &= phase_alternates_;
cycles_per_line_ = cycles_per_line;
unsigned int multiplied_cycles_per_line = cycles_per_line * time_multiplier_;
// generate timing values implied by the given arbuments
// generate timing values implied by the given arguments
sync_capacitor_charge_threshold_ = ((int)(syncCapacityLineChargeThreshold * cycles_per_line) * 3) / 4;
// create the two flywheels
@ -265,16 +266,30 @@ void CRT::advance_cycles(unsigned int number_of_cycles, bool hsync_requested, bo
void CRT::output_scan(const Scan *const scan)
{
const bool this_is_sync = (scan->type == Scan::Type::Sync);
const bool is_trailing_edge = (is_receiving_sync_ && !this_is_sync);
const bool is_leading_edge = (!is_receiving_sync_ && this_is_sync);
is_receiving_sync_ = this_is_sync;
// Accumulate: (i) a total of the amount of time in sync; and (ii) the amount of time since sync.
if(this_is_sync) { cycles_of_sync_ += scan->number_of_cycles; cycles_since_sync_ = 0; }
else cycles_since_sync_ += scan->number_of_cycles;
bool vsync_requested = false;
// If it has been at least half a line since sync ended, then it is safe to decide whether what ended
// was vertical sync.
if(cycles_since_sync_ > (cycles_per_line_ >> 1))
{
// If it was vertical sync, set that flag. If it wasn't, clear the summed amount of sync to avoid
// a mistaken vertical sync due to an aggregate of horizontals.
vsync_requested = (cycles_of_sync_ > sync_capacitor_charge_threshold_);
if(vsync_requested || cycles_of_sync_ < (cycles_per_line_ >> 2))
cycles_of_sync_ = 0;
}
// This introduces a blackout period close to the expected vertical sync point in which horizontal syncs are not
// recognised, effectively causing the horizontal flywheel to freewheel during that period. This attempts to seek
// the problem that vertical sync otherwise often starts halfway through a scanline, which confuses the horizontal
// flywheel. I'm currently unclear whether this is an accurate solution to this problem.
const bool hsync_requested = is_leading_edge && !vertical_flywheel_->is_near_expected_sync();
const bool vsync_requested = is_trailing_edge && (sync_capacitor_charge_level_ >= sync_capacitor_charge_threshold_);
// simplified colour burst logic: if it's within the back porch we'll take it
if(scan->type == Scan::Type::ColourBurst)
@ -293,12 +308,6 @@ void CRT::output_scan(const Scan *const scan)
sync_period_ = is_receiving_sync_ ? (sync_period_ + scan->number_of_cycles) : 0;
advance_cycles(scan->number_of_cycles, hsync_requested, vsync_requested, scan->type);
// either charge or deplete the vertical retrace capacitor (making sure it stops at 0)
if(this_is_sync)
sync_capacitor_charge_level_ += scan->number_of_cycles;
else
sync_capacitor_charge_level_ = std::max(sync_capacitor_charge_level_ - (int)scan->number_of_cycles, 0);
}
/*

5
Outputs/CRT/CRT.hpp
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@ -94,6 +94,11 @@ class CRT {
enqueued_openGL_functions_.push_back(function);
}
// sync counter, for determining vertical sync
unsigned int cycles_of_sync_;
unsigned int cycles_since_sync_;
unsigned int cycles_per_line_;
public:
/*! Constructs the CRT with a specified clock rate, height and colour subcarrier frequency.
The requested number of buffers, each with the requested number of bytes per pixel,