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- Frequently asked questions about the sunxi clock system
- =======================================================
- This document contains useful bits of information that people tend to ask
- about the sunxi clock system, as well as accompanying ASCII art when adequate.
- Q: Why is the main 24MHz oscillator gatable? Wouldn't that break the
- system?
- A: The 24MHz oscillator allows gating to save power. Indeed, if gated
- carelessly the system would stop functioning, but with the right
- steps, one can gate it and keep the system running. Consider this
- simplified suspend example:
- While the system is operational, you would see something like
- 24MHz 32kHz
- |
- PLL1
- \
- \_ CPU Mux
- |
- [CPU]
- When you are about to suspend, you switch the CPU Mux to the 32kHz
- oscillator:
- 24Mhz 32kHz
- | |
- PLL1 |
- /
- CPU Mux _/
- |
- [CPU]
- Finally you can gate the main oscillator
- 32kHz
- |
- |
- /
- CPU Mux _/
- |
- [CPU]
- Q: Were can I learn more about the sunxi clocks?
- A: The linux-sunxi wiki contains a page documenting the clock registers,
- you can find it at
- http://linux-sunxi.org/A10/CCM
- The authoritative source for information at this time is the ccmu driver
- released by Allwinner, you can find it at
- https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu
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