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175 lines
3.9 KiB
C
175 lines
3.9 KiB
C
/**
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******************************************************************************
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* @addtogroup PIOS PIOS Core hardware abstraction layer
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* @{
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* @addtogroup PIOS_DELAY Delay Functions
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* @brief PiOS Delay functionality
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* @{
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*
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* @file pios_delay.c
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* @author Michael Smith Copyright (C) 2011
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* @brief Delay Functions
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* - Provides a micro-second granular delay using the CPU
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* cycle counter.
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* @see The GNU Public License (GPL) Version 3
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*
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*****************************************************************************/
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/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) 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 MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <pios.h>
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#ifdef PIOS_INCLUDE_DELAY
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/* these should be defined by CMSIS, but they aren't */
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#define DWT_CTRL (*(volatile uint32_t *)0xe0001000)
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#define CYCCNTENA (1<<0)
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#define DWT_CYCCNT (*(volatile uint32_t *)0xe0001004)
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/* cycles per microsecond */
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static uint32_t us_ticks;
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/**
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* Initialises the Timer used by PIOS_DELAY functions.
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*
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* \return always zero (success)
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*/
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int32_t PIOS_DELAY_Init(void)
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{
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RCC_ClocksTypeDef clocks;
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/* compute the number of system clocks per microsecond */
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RCC_GetClocksFreq(&clocks);
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us_ticks = clocks.SYSCLK_Frequency / 1000000;
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PIOS_DEBUG_Assert(us_ticks > 1);
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/* turn on access to the DWT registers */
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CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
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/* enable the CPU cycle counter */
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DWT_CTRL |= CYCCNTENA;
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return 0;
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}
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/**
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* Waits for a specific number of uS
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*
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* Example:<BR>
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* \code
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* // Wait for 500 uS
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* PIOS_DELAY_Wait_uS(500);
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* \endcode
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* \param[in] uS delay
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* \return < 0 on errors
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*/
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int32_t PIOS_DELAY_WaituS(uint32_t uS)
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{
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uint32_t elapsed = 0;
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uint32_t last_count = DWT_CYCCNT;
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for (;;) {
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uint32_t current_count = DWT_CYCCNT;
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uint32_t elapsed_uS;
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/* measure the time elapsed since the last time we checked */
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elapsed += current_count - last_count;
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last_count = current_count;
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/* convert to microseconds */
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elapsed_uS = elapsed / us_ticks;
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if (elapsed_uS >= uS)
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break;
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/* reduce the delay by the elapsed time */
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uS -= elapsed_uS;
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/* keep fractional microseconds for the next iteration */
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elapsed %= us_ticks;
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}
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/* No error */
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return 0;
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}
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/**
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* Waits for a specific number of mS
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*
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* Example:<BR>
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* \code
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* // Wait for 500 mS
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* PIOS_DELAY_Wait_mS(500);
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* \endcode
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* \param[in] mS delay
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* \return < 0 on errors
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*/
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int32_t PIOS_DELAY_WaitmS(uint32_t mS)
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{
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while (mS--) {
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PIOS_DELAY_WaituS(1000);
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}
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/* No error */
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return 0;
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}
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/**
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* @brief Query the Delay timer for the current uS
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* @return A microsecond value
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*/
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uint32_t PIOS_DELAY_GetuS(void)
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{
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return DWT_CYCCNT / us_ticks;
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}
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/**
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* @brief Calculate time in microseconds since a previous time
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* @param[in] t previous time
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* @return time in us since previous time t.
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*/
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uint32_t PIOS_DELAY_GetuSSince(uint32_t t)
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{
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return (PIOS_DELAY_GetuS() - t);
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}
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/**
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* @brief Get the raw delay timer, useful for timing
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* @return Unitless value (uint32 wrap around)
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*/
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uint32_t PIOS_DELAY_GetRaw()
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{
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return DWT_CYCCNT;
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}
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/**
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* @brief Compare to raw times to and convert to us
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* @return A microsecond value
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*/
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uint32_t PIOS_DELAY_DiffuS(uint32_t raw)
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{
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uint32_t diff = DWT_CYCCNT - raw;
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return diff / us_ticks;
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}
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#endif /* PIOS_INCLUDE_DELAY */
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/**
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* @}
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* @}
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*/
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