Timing: Difference between revisions

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(notes on some things to look up)
m (→‎CPU: maybe call it S-WRAM)
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* 6-cycles for fast-ROM access, enabled via MEMSEL and accessed at an address of $800000 of higher.
* 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 slow-ROM access.
* 8-cycles for internal WRAM.
* 8-cycles for internal S-WRAM.
* 6-cycles for most [[MMIO registers]].
* 6-cycles for most [[MMIO registers]].
* 12-cycles for [[MMIO registers#JOYSER0|JOYSER0 and JOYSER1]].
* 12-cycles for [[MMIO registers#JOYSER0|JOYSER0 and JOYSER1]].

Revision as of 23:49, 4 June 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 S-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

References

  1. Fullsnes: CPU Clock Cycles