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 /* these should be defined by CMSIS, but they aren't */
  38 #define DWT_CTRL   (*(volatile uint32_t *)0xe0001000)
  39 #define CYCCNTENA  (1 << 0)
  40 #define DWT_CYCCNT (*(volatile uint32_t *)0xe0001004)
  41
  42
  43 /* cycles per microsecond */
  44 static uint32_t us_ticks;
  45
  46 /**
  47  * Initialises the Timer used by PIOS_DELAY functions.
  48  *
  49  * \return always zero (success)
  50  */
  51
  52 int32_t PIOS_DELAY_Init(void)
  53 {
  54     RCC_ClocksTypeDef clocks;
  55
  56     /* compute the number of system clocks per microsecond */
  57     RCC_GetClocksFreq(&clocks);
  58     us_ticks = clocks.SYSCLK_Frequency / 1000000;
  59     PIOS_DEBUG_Assert(us_ticks > 1);
  60
  61     /* turn on access to the DWT registers */
  62     CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
  63
  64     /* enable the CPU cycle counter */
  65     DWT_CTRL |= CYCCNTENA;
  66
  67     return 0;
  68 }
  69
  70 /**
  71  * Waits for a specific number of uS
  72  *
  73  * Example:<BR>
  74  * \code
  75  *   // Wait for 500 uS
  76  *   PIOS_DELAY_Wait_uS(500);
  77  * \endcode
  78  * \param[in] uS delay
  79  * \return < 0 on errors
  80  */
  81 int32_t PIOS_DELAY_WaituS(uint32_t uS)
  82 {
  83     uint32_t elapsed    = 0;
  84     uint32_t last_count = DWT_CYCCNT;
  85
  86     for (;;) {
  87         uint32_t current_count = DWT_CYCCNT;
  88         uint32_t elapsed_uS;
  89
  90         /* measure the time elapsed since the last time we checked */
  91         elapsed   += current_count - last_count;
  92         last_count = current_count;
  93
  94         /* convert to microseconds */
  95         elapsed_uS = elapsed / us_ticks;
  96         if (elapsed_uS >= uS) {
  97             break;
  98         }
  99
 100         /* reduce the delay by the elapsed time */
 101         uS -= elapsed_uS;
 102
 103         /* keep fractional microseconds for the next iteration */
 104         elapsed %= us_ticks;
 105     }
 106
 107     /* No error */
 108     return 0;
 109 }
 110
 111 /**
 112  * Waits for a specific number of mS
 113  *
 114  * Example:<BR>
 115  * \code
 116  *   // Wait for 500 mS
 117  *   PIOS_DELAY_Wait_mS(500);
 118  * \endcode
 119  * \param[in] mS delay
 120  * \return < 0 on errors
 121  */
 122 int32_t PIOS_DELAY_WaitmS(uint32_t mS)
 123 {
 124     while (mS--) {
 125         PIOS_DELAY_WaituS(1000);
 126     }
 127
 128     /* No error */
 129     return 0;
 130 }
 131
 132 /**
 133  * @brief Query the Delay timer for the current uS
 134  * @return A microsecond value
 135  */
 136 uint32_t PIOS_DELAY_GetuS(void)
 137 {
 138     return DWT_CYCCNT / us_ticks;
 139 }
 140
 141 /**
 142  * @brief Calculate time in microseconds since a previous time
 143  * @param[in] t previous time
 144  * @return time in us since previous time t.
 145  */
 146 uint32_t PIOS_DELAY_GetuSSince(uint32_t t)
 147 {
 148     return PIOS_DELAY_GetuS() - t;
 149 }
 150
 151 /**
 152  * @brief Get the raw delay timer, useful for timing
 153  * @return Unitless value (uint32 wrap around)
 154  */
 155 uint32_t PIOS_DELAY_GetRaw()
 156 {
 157     return DWT_CYCCNT;
 158 }
 159
 160 /**
 161  * @brief Compare to raw times to and convert to us
 162  * @return A microsecond value
 163  */
 164 uint32_t PIOS_DELAY_DiffuS(uint32_t raw)
 165 {
 166     uint32_t diff = DWT_CYCCNT - raw;
 167
 168     return diff / us_ticks;
 169 }
 170
 171 #endif /* PIOS_INCLUDE_DELAY */
 172
 173 /**
 174  * @}
 175  * @}
 176  */