flight/pios/stm32f10x/pios_delay.c

   1 /**
   2  ******************************************************************************
   3  * @addtogroup PIOS PIOS Core hardware abstraction layer
   4  * @{
   5  * @addtogroup PIOS_DELAY Delay Functions
   6  * @brief PiOS Delay functionality
   7  * @{
   8  *
   9  * @file       pios_delay.c
  10  * @author     Michael Smith Copyright (C) 2011
  11  * @brief      Delay Functions
  12  *                 - Provides a micro-second granular delay using the CPU
  13  *                   cycle counter.
  14  * @see        The GNU Public License (GPL) Version 3
  15  *
  16  *****************************************************************************/
  17 /*
  18  * This program is free software; you can redistribute it and/or modify
  19  * it under the terms of the GNU General Public License as published by
  20  * the Free Software Foundation; either version 3 of the License, or
  21  * (at your option) any later version.
  22  *
  23  * This program is distributed in the hope that it will be useful, but
  24  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  25  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  26  * for more details.
  27  *
  28  * You should have received a copy of the GNU General Public License along
  29  * with this program; if not, write to the Free Software Foundation, Inc.,
  30  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  31  */
  32
  33 #include <pios.h>
  34
  35 #ifdef PIOS_INCLUDE_DELAY
  36
  37 /* cycles per microsecond */
  38 static uint32_t us_ticks;
  39 static uint32_t raw_hz;
  40
  41 /**
  42  * Initialises the Timer used by PIOS_DELAY functions.
  43  *
  44  * \return always zero (success)
  45  */
  46
  47 int32_t PIOS_DELAY_Init(void)
  48 {
  49     RCC_ClocksTypeDef clocks;
  50
  51     /* compute the number of system clocks per microsecond */
  52     RCC_GetClocksFreq(&clocks);
  53     us_ticks = clocks.SYSCLK_Frequency / 1000000;
  54     PIOS_DEBUG_Assert(us_ticks > 1);
  55     raw_hz   = clocks.SYSCLK_Frequency;
  56
  57     /* turn on access to the DWT registers */
  58     CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
  59
  60     /* enable the CPU cycle counter */
  61     DWT_CTRL |= CYCCNTENA;
  62
  63     return 0;
  64 }
  65
  66 /**
  67  * Waits for a specific number of uS
  68  *
  69  * Example:<BR>
  70  * \code
  71  *   // Wait for 500 uS
  72  *   PIOS_DELAY_Wait_uS(500);
  73  * \endcode
  74  * \param[in] uS delay
  75  * \return < 0 on errors
  76  */
  77 int32_t PIOS_DELAY_WaituS(uint32_t uS)
  78 {
  79     uint32_t elapsed    = 0;
  80     uint32_t last_count = DWT_CYCCNT;
  81
  82     for (;;) {
  83         uint32_t current_count = PIOS_DELAY_GetRaw();
  84         uint32_t elapsed_uS;
  85
  86         /* measure the time elapsed since the last time we checked */
  87         elapsed   += current_count - last_count;
  88         last_count = current_count;
  89
  90         /* convert to microseconds */
  91         elapsed_uS = elapsed / us_ticks;
  92         if (elapsed_uS >= uS) {
  93             break;
  94         }
  95
  96         /* reduce the delay by the elapsed time */
  97         uS -= elapsed_uS;
  98
  99         /* keep fractional microseconds for the next iteration */
 100         elapsed %= us_ticks;
 101     }
 102
 103     /* No error */
 104     return 0;
 105 }
 106
 107 /**
 108  * Waits for a specific number of mS
 109  *
 110  * Example:<BR>
 111  * \code
 112  *   // Wait for 500 mS
 113  *   PIOS_DELAY_Wait_mS(500);
 114  * \endcode
 115  * \param[in] mS delay
 116  * \return < 0 on errors
 117  */
 118 int32_t PIOS_DELAY_WaitmS(uint32_t mS)
 119 {
 120     while (mS--) {
 121         PIOS_DELAY_WaituS(1000);
 122     }
 123
 124     /* No error */
 125     return 0;
 126 }
 127
 128 /**
 129  * @brief Query the Delay timer for the current uS
 130  * @return A microsecond value
 131  */
 132 uint32_t PIOS_DELAY_GetuS(void)
 133 {
 134     return PIOS_DELAY_GetRaw() / us_ticks;
 135 }
 136
 137 /**
 138  * @brief Calculate time in microseconds since a previous time
 139  * @param[in] t previous time
 140  * @return time in us since previous time t.
 141  */
 142 uint32_t PIOS_DELAY_GetuSSince(uint32_t t)
 143 {
 144     return PIOS_DELAY_GetuS() - t;
 145 }
 146
 147 /**
 148  * @brief Get the raw delay timer frequency
 149  * @return raw delay timer frequency in Hz
 150  */
 151 uint32_t PIOS_DELAY_GetRawHz()
 152 {
 153     return raw_hz;
 154 }
 155
 156 /**
 157  * @brief Compare to raw times to and convert to us
 158  * @return A microsecond value
 159  */
 160 uint32_t PIOS_DELAY_DiffuS(uint32_t raw)
 161 {
 162     uint32_t diff = PIOS_DELAY_GetRaw() - raw;
 163
 164     return diff / us_ticks;
 165 }
 166
 167 #endif /* PIOS_INCLUDE_DELAY */
 168
 169 /**
 170  * @}
 171  * @}
 172  */