timer.c

   1 /*
   2  * (C) Copyright 20014 - 2017 Leo C. <erbl259-lmu@yahoo.de>
   3  *
   4  * SPDX-License-Identifier:     GPL-2.0
   5  */
   6
   7 #include "timer.h"
   8 #include <libopencm3/cm3/nvic.h>
   9 #include <libopencm3/cm3/systick.h>
  10 #include <libopencm3/stm32/rcc.h>
  11 #include <libopencm3/stm32/gpio.h>
  12
  13
  14 /*
  15  * timer interrupt/overflow counter, counts up every ms.
  16  */
  17 static
  18 volatile uint32_t timestamp;
  19
  20 void systick_setup(void)
  21 {
  22     /* SysTick interrupt every N clock pulses: set reload to N-1 */
  23     STK_RVR = rcc_ahb_frequency/1000 - 1;
  24
  25     /* Set source to core clock, enable int and start counting. */
  26     STK_CSR = STK_CSR_CLKSOURCE_AHB | STK_CSR_TICKINT | STK_CSR_ENABLE;
  27 }
  28
  29 /*--------------------------------------------------------------------------*/
  30
  31 /*
  32  * 1000Hz timer interrupt generated by System Timer
  33  */
  34 void sys_tick_handler(void)
  35 {
  36         ++timestamp;
  37 }
  38
  39 /*--------------------------------------------------------------------------*/
  40
  41 /*
  42  * Return elapsed time in ms since base.
  43  */
  44 uint32_t get_timer(uint32_t base)
  45 {
  46         return timestamp - base;
  47 }