399e1586be
There are hardware timers whose frequency can't be expressed as ticks-per-microsecond integer-value because only a ticks-per-millisecond integer-value is precise enough. We don't want to use expensive floating-point values here but nonetheless want to translate from ticks to time with microseconds precision. Thus, we split the input in two and translate both parts separately. This way, we can raise precision by shifting the values to their optimal bit position. Afterwards, the results are shifted back and merged together again. As this algorithm is not so trivial anymore and used by at least three timer drivers (base-hw/x86_64, base-hw/cortex_a9, timer/pit), move it to a generic header to avoid redundancy. Ref #2400
69 lines
1.6 KiB
C++
69 lines
1.6 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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/* Genode includes */
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#include <drivers/timer/util.h>
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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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static_assert(TICS_PER_MS >= 1000, "Bad TICS_PER_MS value");
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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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return timer_ticks_to_us(ticks, Driver::TICS_PER_MS); }
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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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