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LibrePilot/flight/pios/stm32f4xx/pios_delay.c
2016-06-18 14:08:05 -04:00

188 lines
4.4 KiB
C

/**
******************************************************************************
* @addtogroup PIOS PIOS Core hardware abstraction layer
* @{
* @addtogroup PIOS_DELAY Delay Functions
* @brief PiOS Delay functionality
* @{
*
* @file pios_delay.c
* @author Michael Smith Copyright (C) 2012
* @brief Delay Functions
* - Provides a micro-second granular delay using the CPU
* cycle counter.
* @see The GNU Public License (GPL) Version 3
*
*****************************************************************************/
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <pios.h>
#ifdef PIOS_INCLUDE_DELAY
/* these should be defined by CMSIS, but they aren't */
#define DWT_CTRL (*(volatile uint32_t *)0xe0001000)
#define CYCCNTENA (1 << 0)
#define DWT_CYCCNT (*(volatile uint32_t *)0xe0001004)
/* cycles per microsecond */
static uint32_t us_ticks;
/**
* Initialises the Timer used by PIOS_DELAY functions.
*
* \return always zero (success)
*/
int32_t PIOS_DELAY_Init(void)
{
RCC_ClocksTypeDef clocks;
/* compute the number of system clocks per microsecond */
RCC_GetClocksFreq(&clocks);
us_ticks = clocks.SYSCLK_Frequency / 1000000;
PIOS_DEBUG_Assert(us_ticks > 1);
/* turn on access to the DWT registers */
CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
/* enable the CPU cycle counter */
DWT_CTRL |= CYCCNTENA;
return 0;
}
/**
* Waits for a specific number of uS
*
* Example:<BR>
* \code
* // Wait for 500 uS
* PIOS_DELAY_Wait_uS(500);
* \endcode
* \param[in] uS delay
* \return < 0 on errors
*/
int32_t PIOS_DELAY_WaituS(uint32_t uS)
{
uint32_t elapsed = 0;
uint32_t last_count = DWT_CYCCNT;
for (;;) {
uint32_t current_count = DWT_CYCCNT;
uint32_t elapsed_uS;
/* measure the time elapsed since the last time we checked */
elapsed += current_count - last_count;
last_count = current_count;
/* convert to microseconds */
elapsed_uS = elapsed / us_ticks;
if (elapsed_uS >= uS) {
break;
}
/* reduce the delay by the elapsed time */
uS -= elapsed_uS;
/* keep fractional microseconds for the next iteration */
elapsed %= us_ticks;
}
/* No error */
return 0;
}
/**
* Waits for a specific number of mS
*
* Example:<BR>
* \code
* // Wait for 500 mS
* PIOS_DELAY_Wait_mS(500);
* \endcode
* \param[in] mS delay (1..65535 milliseconds)
* \return < 0 on errors
*/
int32_t PIOS_DELAY_WaitmS(uint32_t mS)
{
while (mS--) {
PIOS_DELAY_WaituS(1000);
}
/* No error */
return 0;
}
/**
* @brief Query the Delay timer for the current uS
* @return A microsecond value
*/
uint32_t PIOS_DELAY_GetuS()
{
return DWT_CYCCNT / us_ticks;
}
/**
* @brief Calculate time in microseconds since a previous time
* @param[in] t previous time
* @return time in us since previous time t.
*/
uint32_t PIOS_DELAY_GetuSSince(uint32_t t)
{
return PIOS_DELAY_GetuS() - t;
}
/**
* @brief Get the raw delay timer, useful for timing
* @return Unitless value (uint32 wrap around)
*/
uint32_t PIOS_DELAY_GetRaw()
{
return DWT_CYCCNT;
}
/**
* @brief Compare to raw times to and convert to us
* @return A microsecond value
*/
uint32_t PIOS_DELAY_DiffuS(uint32_t raw)
{
uint32_t diff = DWT_CYCCNT - raw;
return diff / us_ticks;
}
#if !defined(PIOS_EXCLUDE_ADVANCED_FEATURES)
/**
* @brief Subrtact two raw times and convert to us.
* @return Interval between raw times in microseconds
*/
uint32_t PIOS_DELAY_DiffuS2(uint32_t raw, uint32_t later)
{
return (later - raw) / us_ticks;
}
#endif /* !defined(PIOS_EXCLUDE_ADVANCED_FEATURES) */
#endif /* PIOS_INCLUDE_DELAY */
/**
* @}
* @}
*/