Timing: Difference between revisions
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Timing of the SNES hardware. | |||
== Master Clock == | |||
The SNES master clock: | The SNES master clock: | ||
* NTSC 21.447 MHz | * NTSC 21.447 MHz | ||
* PAL 21.281 MHz | * PAL 21.281 MHz | ||
== CPU == | |||
A 65816 CPU "cycle" can take 6, 8 or 12 master cycles on the SNES, depending on the memory region accessed, and the [[MMIO registers#MEMSEL|MEMSEL]] fast-ROM setting. | A 65816 CPU "cycle" can take 6, 8 or 12 master cycles on the SNES, depending on the memory region accessed, and the [[MMIO registers#MEMSEL|MEMSEL]] fast-ROM setting. | ||
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* 12-cycles for [[MMIO registers#JOYSER0|JOYSER0 and JOYSER1]]. | * 12-cycles for [[MMIO registers#JOYSER0|JOYSER0 and JOYSER1]]. | ||
* 6-cycles for "internal" cycles not accessing memory (e.g. 2nd cycle of NOP) | * 6-cycles for "internal" cycles not accessing memory (e.g. 2nd cycle of NOP) | ||
== Video == | |||
TODO: | |||
* Cycles per scanline | |||
* Cycles per frame | |||
* Cycles per vblank | |||
* Vblank DMA budgets | |||
* Scanlines per frame | |||
== References == | == References == | ||
<References/> | <References/> | ||
Revision as of 03:59, 26 May 2022
Timing of the SNES hardware.
Master Clock
The SNES master clock:
- NTSC 21.447 MHz
- PAL 21.281 MHz
CPU
A 65816 CPU "cycle" can take 6, 8 or 12 master cycles on the SNES, depending on the memory region accessed, and the MEMSEL fast-ROM setting.
This gives some commonly quoted SNES CPU speeds, though none of them tell a complete story:
- 3.58 MHz fast-ROM (6-cycle)
- 2.68 MHz slow-ROM (8-cycle)
- 1.79 MHz other (12-cycle)
The speed of access depends on the memory region:[1]
- 6-cycles for fast-ROM access, enabled via MEMSEL and accessed at an address of $800000 of higher.
- 8-cycles for slow-ROM access.
- 8-cycles for internal WRAM.
- 6-cycles for most MMIO registers.
- 12-cycles for JOYSER0 and JOYSER1.
- 6-cycles for "internal" cycles not accessing memory (e.g. 2nd cycle of NOP)
Video
TODO:
- Cycles per scanline
- Cycles per frame
- Cycles per vblank
- Vblank DMA budgets
- Scanlines per frame
