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/*
* This file is part of the libopencm3 project.
*
* Copyright (C) 2010 Thomas Otto <tommi@viadmin.org>
* Copyright (C) 2012 Benjamin Vernoux <titanmkd@gmail.com>
*
* This library is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
/** @defgroup CM3_systick_file SysTick
*
* @ingroup CM3_files
*
* @brief <b>libopencm3 Cortex System Tick Timer</b>
*
* @version 1.0.0
*
* @author @htmlonly © @endhtmlonly 2010 Thomas Otto <tommi@viadmin.org>
*
* @date 19 August 2012
*
* This library supports the System Tick timer in ARM Cortex Microcontrollers.
*
* The System Tick timer is part of the ARM Cortex core. It is a 24 bit
* down counter that can be configured with an automatical reload value.
*
* LGPL License Terms @ref lgpl_license
*/
/**@{*/
#include <libopencm3/cm3/systick.h>
/*---------------------------------------------------------------------------*/
/** @brief SysTick Set the Automatic Reload Value.
*
* The counter is set to the reload value when the counter starts and after it
* reaches zero.
*
* @note The systick counter value might be undefined upon startup. To get
* predictable behavior, it is a good idea to set or clear the counter after
* set reload. @seealso systick_clear
*
* @param[in] value uint32_t. 24 bit reload value.
*/
void systick_set_reload(uint32_t value)
{
STK_RVR = (value & STK_RVR_RELOAD);
}
/*---------------------------------------------------------------------------*/
/** @brief SysTick Read the Automatic Reload Value.
*
* @returns 24 bit reload value as uint32_t.
*/
uint32_t systick_get_reload(void)
{
return STK_RVR & STK_RVR_RELOAD;
}
/** @brief SysTick Set clock and frequency of overflow
*
* This function sets the systick to AHB clock source, and the prescaler to
* generate interrupts with the desired frequency. The function fails, if
* the frequency is too low.
*
* @param[in] freq uint32_t The desired frequency in Hz
* @param[in] ahb uint32_t The current AHB frequency in Hz
* @returns true, if success, false if the desired frequency cannot be set.
*/
bool systick_set_frequency(uint32_t freq, uint32_t ahb)
{
uint32_t ratio = ahb / freq;
#if defined(__ARM_ARCH_6M__)
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
#else
if (ratio >= (STK_RVR_RELOAD * 8)) {
/* This frequency is too slow */
return false;
} else if (ratio >= STK_RVR_RELOAD) {
ratio /= 8;
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB_DIV8);
} else {
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
}
#endif
systick_set_reload(ratio - 1);
return true;
}
/*---------------------------------------------------------------------------*/
/** @brief Get the current SysTick counter value.
*
* @returns 24 bit current value as uint32_t.
*/
uint32_t systick_get_value(void)
{
return STK_CVR & STK_CVR_CURRENT;
}
/*---------------------------------------------------------------------------*/
/** @brief Set the SysTick Clock Source.
*
* The clock source can be either the AHB clock or the same clock divided by 8.
*
* @param[in] clocksource uint8_t. Clock source from @ref systick_clksource.
*/
void systick_set_clocksource(uint8_t clocksource)
{
STK_CSR = (STK_CSR & ~STK_CSR_CLKSOURCE) |
(clocksource & STK_CSR_CLKSOURCE);
}
/*---------------------------------------------------------------------------*/
/** @brief Enable SysTick Interrupt.
*
*/
void systick_interrupt_enable(void)
{
STK_CSR |= STK_CSR_TICKINT;
}
/*---------------------------------------------------------------------------*/
/** @brief Disable SysTick Interrupt.
*
*/
void systick_interrupt_disable(void)
{
STK_CSR &= ~STK_CSR_TICKINT;
}
/*---------------------------------------------------------------------------*/
/** @brief Enable SysTick Counter.
*
*/
void systick_counter_enable(void)
{
STK_CSR |= STK_CSR_ENABLE;
}
/*---------------------------------------------------------------------------*/
/** @brief Disable SysTick Counter.
*
*/
void systick_counter_disable(void)
{
STK_CSR &= ~STK_CSR_ENABLE;
}
/*---------------------------------------------------------------------------*/
/** @brief SysTick Read the Counter Flag.
*
* The count flag is set when the timer count becomes zero, and is cleared when
* the flag is read.
*
* @returns Boolean if flag set.
*/
uint8_t systick_get_countflag(void)
{
return (STK_CSR & STK_CSR_COUNTFLAG) ? 1 : 0;
}
/*---------------------------------------------------------------------------*/
/** @brief SysTick Clear counter Value.
*
* The counter value is cleared. Useful for well defined startup.
*/
void systick_clear(void)
{
STK_CVR = 0;
}
/*---------------------------------------------------------------------------*/
/** @brief SysTick Get Calibration Value
*
* @returns Current calibration value
*/
uint32_t systick_get_calib(void)
{
return STK_CALIB & STK_CALIB_TENMS;
}
/**@}*/
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