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https://github.com/projectacrn/acrn-kernel.git
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1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
66 lines
2.4 KiB
Plaintext
66 lines
2.4 KiB
Plaintext
Clock scaling
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-------------
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The kernel supports scaling of CLCK.CMODE, CLCK.CM and CLKC.P0 clock
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registers. If built with CONFIG_PM and CONFIG_SYSCTL options enabled, four
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extra files will appear in the directory /proc/sys/pm/. Reading these files
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will show:
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p0 -- current value of the P0 bit in CLKC register.
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cm -- current value of the CM bits in CLKC register.
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cmode -- current value of the CMODE bits in CLKC register.
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On all boards, the 'p0' file should also be writable, and either '1' or '0'
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can be rewritten, to set or clear the CLKC_P0 bit respectively, hence
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controlling whether the resource bus rate clock is halved.
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The 'cm' file should also be available on all boards. '0' can be written to it
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to shift the board into High-Speed mode (normal), and '1' can be written to
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shift the board into Medium-Speed mode. Selecting Low-Speed mode is not
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supported by this interface, even though some CPUs do support it.
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On the boards with FR405 CPU (i.e. CB60 and CB70), the 'cmode' file is also
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writable, allowing the CPU core speed (and other clock speeds) to be
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controlled from userspace.
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Determining current and possible settings
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-----------------------------------------
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The current state and the available masks can be found in /proc/cpuinfo. For
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example, on the CB70:
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# cat /proc/cpuinfo
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CPU-Series: fr400
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CPU-Core: fr405, gr0-31, BE, CCCR
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CPU: mb93405
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MMU: Prot
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FP-Media: fr0-31, Media
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System: mb93091-cb70, mb93090-mb00
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PM-Controls: cmode=0xd31f, cm=0x3, p0=0x3, suspend=0x9
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PM-Status: cmode=3, cm=0, p0=0
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Clock-In: 50.00 MHz
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Clock-Core: 300.00 MHz
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Clock-SDRAM: 100.00 MHz
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Clock-CBus: 100.00 MHz
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Clock-Res: 50.00 MHz
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Clock-Ext: 50.00 MHz
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Clock-DSU: 25.00 MHz
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BogoMips: 300.00
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And on the PDK, the PM lines look like the following:
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PM-Controls: cm=0x3, p0=0x3, suspend=0x9
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PM-Status: cmode=9, cm=0, p0=0
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The PM-Controls line, if present, will indicate which /proc/sys/pm files can
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be set to what values. The specification values are bitmasks; so, for example,
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"suspend=0x9" indicates that 0 and 3 can be written validly to
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/proc/sys/pm/suspend.
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The PM-Controls line will only be present if CONFIG_PM is configured to Y.
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The PM-Status line indicates which clock controls are set to which value. If
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the file can be read, then the suspend value must be 0, and so that's not
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included.
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