889db34cc3
A bug in the timer-ticks-to-microseconds translation of the kernel timer caused the user time to periodically get stuck for about 32 milliseconds and then jump forward to the normal level again. Ref #2400
88 lines
2.4 KiB
C++
88 lines
2.4 KiB
C++
/*
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* \brief Timer implementation specific to Cortex A9
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* \author Stefan Kalkowski
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* \author Martin Stein
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* \date 2016-01-07
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*/
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/*
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* Copyright (C) 2016-2017 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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/* core includes */
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#include <kernel/timer.h>
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#include <platform.h>
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using namespace Genode;
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using namespace Kernel;
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Timer_driver::Timer_driver(unsigned)
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: Mmio(Platform::mmio_to_virt(Board::Cpu_mmio::PRIVATE_TIMER_MMIO_BASE))
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{
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write<Control::Timer_enable>(0);
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}
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void Timer::_start_one_shot(time_t const ticks)
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{
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enum { PRESCALER = Board::CORTEX_A9_PRIVATE_TIMER_DIV - 1 };
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/* reset timer */
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_driver.write<Driver::Interrupt_status::Event>(1);
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Driver::Control::access_t control = 0;
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Driver::Control::Irq_enable::set(control, 1);
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Driver::Control::Prescaler::set(control, PRESCALER);
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_driver.write<Driver::Control>(control);
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/* load timer and start decrementing */
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_driver.write<Driver::Load>(ticks);
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_driver.write<Driver::Control::Timer_enable>(1);
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}
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time_t Timer::_ticks_to_us(time_t const ticks) const
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{
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/*
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* If we would do the translation with one division and
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* multiplication over the whole argument, we would loose
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* microseconds granularity although the timer frequency would
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* allow for such granularity. Thus, we treat the most significant
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* half and the least significant half of the argument separate.
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* Each half is shifted to the best bit position for the
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* translation, then translated, and then shifted back.
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*/
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static_assert(Driver::TICS_PER_MS >= 1000, "Bad TICS_PER_MS value");
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enum {
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HALF_WIDTH = (sizeof(time_t) << 2),
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MSB_MASK = ~0UL << HALF_WIDTH,
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LSB_MASK = ~0UL >> HALF_WIDTH,
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MSB_RSHIFT = 10,
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LSB_LSHIFT = HALF_WIDTH - MSB_RSHIFT,
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};
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time_t const msb = ((((ticks & MSB_MASK) >> MSB_RSHIFT)
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* 1000) / Driver::TICS_PER_MS) << MSB_RSHIFT;
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time_t const lsb = ((((ticks & LSB_MASK) << LSB_LSHIFT)
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* 1000) / Driver::TICS_PER_MS) >> LSB_LSHIFT;
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return msb + lsb;
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}
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unsigned Timer::interrupt_id() const {
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return Board::Cpu_mmio::PRIVATE_TIMER_IRQ; }
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time_t Timer::us_to_ticks(time_t const us) const {
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return (us / 1000) * Driver::TICS_PER_MS; }
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time_t Timer::_value() {
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return _driver.read<Driver::Counter>(); }
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time_t Timer::_max_value() const {
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return (Driver::Load::access_t)~0; }
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