58 lines · plain
1=======================================================2Frequently asked questions about the sunxi clock system3=======================================================4 5This document contains useful bits of information that people tend to ask6about the sunxi clock system, as well as accompanying ASCII art when adequate.7 8Q: Why is the main 24MHz oscillator gateable? Wouldn't that break the9 system?10 11A: The 24MHz oscillator allows gating to save power. Indeed, if gated12 carelessly the system would stop functioning, but with the right13 steps, one can gate it and keep the system running. Consider this14 simplified suspend example:15 16 While the system is operational, you would see something like::17 18 24MHz 32kHz19 |20 PLL121 \22 \_ CPU Mux23 |24 [CPU]25 26 When you are about to suspend, you switch the CPU Mux to the 32kHz27 oscillator::28 29 24Mhz 32kHz30 | |31 PLL1 |32 /33 CPU Mux _/34 |35 [CPU]36 37 Finally you can gate the main oscillator::38 39 32kHz40 |41 |42 /43 CPU Mux _/44 |45 [CPU]46 47Q: Were can I learn more about the sunxi clocks?48 49A: The linux-sunxi wiki contains a page documenting the clock registers,50 you can find it at51 52 http://linux-sunxi.org/A10/CCM53 54 The authoritative source for information at this time is the ccmu driver55 released by Allwinner, you can find it at56 57 https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu58