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140 lines
3.7 KiB
C
140 lines
3.7 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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/* these should be defined by CMSIS, but they aren't */
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#define DWT_CTRL (*(volatile unsigned long *)0xe0001000)
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#define DWT_CYCCNT (*(volatile unsigned long *)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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/* 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 |= 1;
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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 (1..65535 microseconds)
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* \return < 0 on errors
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*/
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int32_t PIOS_DELAY_WaituS(uint16_t uS)
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{
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uint32_t deadline;
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/*
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* This logic is mildly sneaky and depends on C's casting behaviour from
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* unsigned to signed when the MSB is set.
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*
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* We also depend on the difference between the deadline and DWT_CYCCNT
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* never starting off at more than half of the counter period. Since we
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* can't be asked to wait more than 65.5ms, the counter would have to wrap
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* in 131ms (approx 32THz for the 32-bit counter) for this to be a problem.
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*
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* If we are stopped by the debugger for more than half the counter period,
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* and the cycle counter doesn't stop (it normally does), the delay will be
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* protracted.
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*/
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deadline = DWT_CYCCNT + (uS * us_ticks);
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while ((int32_t)(deadline - DWT_CYCCNT) > 0) {
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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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* If FreeRTOS is configured, and the delay is longer than a tick, wait whole
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* ticks using the RTOS. Fractional remainders or periods shorter than a tick
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* are busy-waited.
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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 (1..65535 milliseconds)
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* \return < 0 on errors
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*/
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int32_t PIOS_DELAY_WaitmS(uint16_t mS)
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{
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#if 0 // XXX cannot do this if the scheduler hasn't started yet...
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#ifdef PIOS_INCLUDE_FREERTOS
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if (mS > portTICK_RATE_MS) {
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vTaskDelay(mS / portTICK_RATE_MS);
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mS = mS % portTICK_RATE_MS;
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}
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#endif
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#endif
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for (int i = 0; i < mS; i++) {
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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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* @}
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* @}
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*/
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