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 gateable? 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