51 lines
2.6 KiB
Plaintext
51 lines
2.6 KiB
Plaintext
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#=----------------------------------------------------------------------------=#
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# GNU GPL OS/K Documentation #
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# #
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# Desc: OS/K Loader : CPU Management functions #
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# #
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# #
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# Copyright © 2018-2020 The OS/K Team #
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# #
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# Permission is granted to copy, distribute and/or modify this #
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# document under the terms of the GNU Free Documentation License, #
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# Version 1.3 or any later version published by the Free Software #
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# Foundation; with no Invariant Sections, no Front-Cover Texts, and #
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# no Back-Cover Texts. A copy of the license is included in the #
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# file entitled "COPYING.GFDL" #
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#=----------------------------------------------------------------------------=#
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This folder contains two files, `boot/loader/cpu/cpu.inc` and
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boot/loader/cpu/cpu32.inc`.
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The `boot/loader/cpu/cpu32.inc` is intented to provide 32 bits protected mode
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function that can control wether the CPU is qualified to run the OS/K code.
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The `boot/loader/cpu/cpu3.inc` provides 64 bits long mode temporization function
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used by the loader when necessary.
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There is two functions in `cpu32.inc` :
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- Is64Bits(), intented to check if the CPU is "ok" with 64 bit code,
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if it supports long mode and will not burn if we ask it to execute OS/K
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(i.e trigger a #UD fault).
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For this check, we use first the 0x80000000 function of the CPUID instruction
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that returns the highest CPUID function available. It must return at least
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0x80000001, otherwise we can't check the long mode presence and it is most
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likely absent. We pass the function number in the eax register.
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As soon as 0x80000001 is available, we use it and verify it flips to 1 the bit
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29 in edx.
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- Check_cpuid(), that check if the CPUID instruction is supported by the CPU
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before use it (don't want #UD).
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For this, we use the FLAGS register and check if we can flip (overwrite with
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a 1 persistantly) the bit 21. If it is possible, then CPUID is supported.
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The temporize(), bitemporize() and tritemporize() functions in `cpu.inc`
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are juste loops that make the cpu busy to wait. These temporization are not
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precise at all, and are not intented to wait for a determined time lapse.
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