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8b0415d905
The small bootloaders (CC and PipX) are out of flash space so their stopwatch implementation has been swapped out for one based on the DELAY clock that takes about 500 bytes less of code space. Identical functionality is preserved.
157 lines
3.6 KiB
C
157 lines
3.6 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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/* Project Includes */
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#include <pios.h>
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#if defined(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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#endif
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/**
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* @}
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* @}
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*/
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