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