mirror of
https://github.com/RetroPortingToolKit/psxrecomp
synced 2026-10-26 10:19:47 -04:00
Matthew Stanley
63 lines
2.6 KiB
C
63 lines
2.6 KiB
C
/*
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* frame_pacing.h — race-free wall-clock frame pacing.
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*
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* Replaces the open-coded pacing loops in main.cpp (sdl_vblank_present)
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* and beetle_main.cpp. The open-coded version read the performance
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* counter twice per iteration (once in the while-condition, once to
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* compute the remaining time); if the deadline was crossed between the
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* two reads — a preemption-sized window — the unsigned subtraction
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* underflowed and SDL_Delay received a ~24.7-day argument (2^64 ticks
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* * 1000 / 10 MHz, truncated to Uint32). That was the Bug B hard
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* freeze: the app parks in one SDL_Delay with every counter frozen,
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* wedged between `i_stat |= VBLANK` and exception delivery.
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*
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* Rules the implementation must keep:
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* - exactly ONE counter read per decision; compare before subtract
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* - the computed sleep is clamped to one frame period
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* - a deadline already in the past never sleeps
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*/
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#ifndef FRAME_PACING_H
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#define FRAME_PACING_H
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#include <stdint.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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typedef struct FramePacer {
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uint64_t next_deadline; /* perf-counter ticks; 0 = not started */
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} FramePacer;
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/* Pure decision function (unit-testable, no SDL).
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* Given a single counter sample `now`, the current deadline, the counter
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* frequency and the frame period (both in ticks), returns the number of
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* milliseconds to sleep right now, or 0 if the caller should stop
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* sleeping (deadline reached / close enough to spin).
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* Never returns a value larger than one period's worth of ms + 1. */
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uint32_t frame_pacing_sleep_ms(uint64_t now, uint64_t deadline,
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uint64_t freq, uint64_t period);
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/* Block until the pacer's next deadline (sleep + final sub-ms spin),
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* then advance the deadline by one period. If the pacer has not started,
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* or the caller fell beyond the implementation's bounded transient-catch-up
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* window, re-anchor to now + period without sleeping. period_ms is the frame
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* period in milliseconds (e.g. 1000.0 / 59.94). */
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void frame_pacer_wait(FramePacer *p, double period_ms);
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/* 1 when the panel matches guest cadence and synchronized swaps can supply
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* the guest's VBlank clock (present_vsync_owns_cadence() in main.cpp). The
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* deadline pacer still caps speed if the driver does not actually block.
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* Faster panels can also synchronize swaps while the pacer owns guest timing;
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* this query then returns 0.
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*
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* A renderer that elides a redundant swap (unchanged front buffer) must
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* therefore retain it while this is 1 to preserve display-clock pacing. */
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int psx_present_vsync_owns_cadence(void);
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#ifdef __cplusplus
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}
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#endif
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#endif /* FRAME_PACING_H */
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