LibrePilot/flight/pios/stm32f4xx/pios_delay.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;
}

#endif /* PIOS_INCLUDE_DELAY */

/**
 * @}
 * @}
 */