mirror of
https://github.com/RetroPortingToolKit/psxrecomp
synced 2026-10-26 02:11:36 -04:00
Matthew Stanley
72 lines
2.9 KiB
C
72 lines
2.9 KiB
C
#ifndef PSXRECOMP_PSX_VIDEO_TIMING_H
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#define PSXRECOMP_PSX_VIDEO_TIMING_H
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/* Frame timing follows the GPU's live video standard.
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*
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* On hardware the scanline count per frame (NTSC 263 / PAL 314) and so the
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* VBlank rate come from GP1(08h) bit 3, whatever the console or disc region.
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* The GPU reports every change of that bit here (GP1(08h), GP1(00h) reset,
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* power-on, snapshot restore); VBlank scheduling (interrupts.c), the Timer 1
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* HBlank clock (timers.c) and host frame pacing (main.cpp) all read it.
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*
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* The frame period is live: the frame in progress ends once its elapsed
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* cycles reach the CURRENT standard's period, the way a scanline counter
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* running against the new line total would end the field. From the next
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* frame on the period is exactly the new standard's. No extra state is
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* needed across savestates: the GPU snapshot carries the mode bit.
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*
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* The periods keep the framework's round 60/50 Hz constants so NTSC timing
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* is bit-identical to the region-only model this replaces. */
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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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#define PSX_VBLANK_CYCLES_NTSC 564480u /* 33.8688 MHz / 60 Hz */
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#define PSX_VBLANK_CYCLES_PAL 677376u /* 33.8688 MHz / 50 Hz */
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#define PSX_LINES_PER_FRAME_NTSC 263u
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#define PSX_LINES_PER_FRAME_PAL 314u
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/* Timer 1 HBlank clock: one frame's cycles spread over its scanlines,
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* truncated (NTSC 564480 / 263 = 2146, PAL 677376 / 314 = 2157). */
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#define PSX_HBLANK_CYCLES_NTSC (PSX_VBLANK_CYCLES_NTSC / PSX_LINES_PER_FRAME_NTSC)
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#define PSX_HBLANK_CYCLES_PAL (PSX_VBLANK_CYCLES_PAL / PSX_LINES_PER_FRAME_PAL)
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/* Live values for the current standard. Written only through
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* psx_video_timing_set_pal(); read on hot paths. */
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extern uint32_t g_psx_vblank_cycles;
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extern uint32_t g_psx_hblank_cycles;
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extern uint32_t g_psx_lines_per_frame;
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/* GP1(08h) display-mode word -> 1 when bit 3 selects PAL. */
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static inline int psx_gp1_display_mode_is_pal(uint32_t word) {
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return (int)((word >> 3) & 1u);
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}
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/* Select the video standard. Returns 1 when it changed. */
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int psx_video_timing_set_pal(int pal);
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int psx_video_timing_is_pal(void);
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/* Bumped on every change; host-side observers (pacing) compare it. */
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uint32_t psx_video_timing_generation(void);
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/* VBlank edge bookkeeping on the cycles elapsed since the last edge. */
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static inline int psx_vblank_edge_due(uint32_t cycles_since_vblank) {
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return cycles_since_vblank >= g_psx_vblank_cycles;
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}
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static inline uint32_t psx_vblank_cycles_to_edge(uint32_t cycles_since_vblank) {
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return cycles_since_vblank >= g_psx_vblank_cycles
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? 0u : g_psx_vblank_cycles - cycles_since_vblank;
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}
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/* Consume one due edge. Subtracts one period rather than resetting to 0 so
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* cycle overshoot carries into the next frame. */
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static inline void psx_vblank_consume_edge(uint32_t *cycles_since_vblank) {
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*cycles_since_vblank -= g_psx_vblank_cycles;
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}
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#ifdef __cplusplus
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}
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#endif
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#endif
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