1======================================================= 2Frequently asked questions about the sunxi clock system 3======================================================= 4 5This document contains useful bits of information that people tend to ask 6about the sunxi clock system, as well as accompanying ASCII art when adequate. 7 8Q: Why is the main 24MHz oscillator gatable? Wouldn't that break the 9 system? 10 11A: The 24MHz oscillator allows gating to save power. Indeed, if gated 12 carelessly the system would stop functioning, but with the right 13 steps, one can gate it and keep the system running. Consider this 14 simplified suspend example: 15 16 While the system is operational, you would see something like:: 17 18 24MHz 32kHz 19 | 20 PLL1 21 \ 22 \_ CPU Mux 23 | 24 [CPU] 25 26 When you are about to suspend, you switch the CPU Mux to the 32kHz 27 oscillator:: 28 29 24Mhz 32kHz 30 | | 31 PLL1 | 32 / 33 CPU Mux _/ 34 | 35 [CPU] 36 37 Finally you can gate the main oscillator:: 38 39 32kHz 40 | 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 at 51 52 http://linux-sunxi.org/A10/CCM 53 54 The authoritative source for information at this time is the ccmu driver 55 released by Allwinner, you can find it at 56 57 https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu 58