| 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 |