302f1eeb80
Allow the active timer (providing udelay() and currticks()) to be selected at runtime based on probing during the INIT_EARLY stage of initialisation. TICKS_PER_SEC is now a fixed compile-time constant for all builds, and is independent of the underlying clock tick rate. We choose the value 1024 to allow multiplications and divisions on seconds to be converted to bit shifts. TICKS_PER_MS is defined as 1, allowing multiplications and divisions on milliseconds to be omitted entirely. The 2% inaccuracy in this definition is negligible when using the standard BIOS timer (running at around 18.2Hz). TIMER_RDTSC now checks for a constant TSC before claiming to be a usable timer. (This timer can be tested in KVM via the command-line option "-cpu host,+invtsc".) Signed-off-by: Michael Brown <mcb30@ipxe.org>
82 lines
2.1 KiB
C
82 lines
2.1 KiB
C
/*
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* Copyright (C) 2010 Piotr Jaroszyński <p.jaroszynski@gmail.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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FILE_LICENCE(GPL2_OR_LATER);
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#include <stddef.h>
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#include <ipxe/timer.h>
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#include <linux_api.h>
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/** @file
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*
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* iPXE timer API for linux
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*
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*/
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/**
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* Delay for a fixed number of microseconds
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*
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* @v usecs Number of microseconds for which to delay
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*/
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static void linux_udelay(unsigned long usecs)
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{
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linux_usleep(usecs);
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}
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/**
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* Get current system time in ticks
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*
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* linux doesn't provide an easy access to jiffies so implement it by measuring
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* the time since the first call to this function.
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*
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* Since this function is used to seed the (non-cryptographic) random
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* number generator, we round the start time down to the nearest whole
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* second. This minimises the chances of generating identical RNG
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* sequences (and hence identical TCP port numbers, etc) on
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* consecutive invocations of iPXE.
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*
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* @ret ticks Current time, in ticks
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*/
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static unsigned long linux_currticks(void)
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{
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static struct timeval start;
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static int initialized = 0;
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struct timeval now;
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unsigned long ticks;
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if (! initialized) {
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linux_gettimeofday(&start, NULL);
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initialized = 1;
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}
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linux_gettimeofday(&now, NULL);
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ticks = ( ( now.tv_sec - start.tv_sec ) * TICKS_PER_SEC );
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ticks += ( now.tv_usec / ( 1000000 / TICKS_PER_SEC ) );
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return ticks;
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}
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/** Linux timer */
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struct timer linux_timer __timer ( TIMER_NORMAL ) = {
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.name = "linux",
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.currticks = linux_currticks,
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.udelay = linux_udelay,
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};
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