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x86_64: Update comments in pit.c

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K. Lange 2024-01-22 07:57:39 +09:00
parent 4a1b944525
commit f6e2c36d73
1 changed files with 3 additions and 17 deletions
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kernel/arch/x86_64/pit.c
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@ -3,27 +3,13 @@
* @author K. Lange * @author K. Lange
* @brief Legacy x86 Programmable Interrupt Timer * @brief Legacy x86 Programmable Interrupt Timer
* *
* Trusty old timer chip that still exists, and is still somehow * The PIT is used as a fallback preempt source if the LAPIC can
* the only reliable to measure subsecond wallclock times. * not be configured. The preempt signal is 100Hz.
*
* We continue to the use the PIT as the BSP timer interrupt source,
* and we also use it as part of timer calibration for TSCs, which
* is then used to calibrate LAPIC timers.
*
* Our main tick rate is 100Hz. We use periodic modes, so this
* doesn't equate to 1/100s worth of CPU time per process before
* it gets switched out, rather something less usually, but it
* does mean we don't need to care about resetting timers or
* even knowing which timer triggered a userspace pre-emption, since
* APs use their LAPIC timers (which we also try to set to 100Hz).
*
* The actual time doesn't matter, as we don't use the PIT as a real
* timing source after initialization of the TSC. 100Hz just feels nice?
* *
* @copyright * @copyright
* This file is part of ToaruOS and is released under the terms * This file is part of ToaruOS and is released under the terms
* of the NCSA / University of Illinois License - see LICENSE.md * of the NCSA / University of Illinois License - see LICENSE.md
* Copyright (C) 2021 K. Lange * Copyright (C) 2021-2024 K. Lange
*/ */
#include <kernel/printf.h> #include <kernel/printf.h>
#include <kernel/process.h> #include <kernel/process.h>