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This is a demo that uses the System Tick counter in the STM32F4

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as a way of creating accurately timed delays. A simple 'msleep'
is implemented by watching the system clock to wait a certain
number of milleseconds before it returns. Its a bit more accurate
than a for loop, although it really shines when your running multiple
threads.
This commit is contained in:
Chuck McManis
2013-07-12 19:24:39 -07:00
committed by Piotr Esden-Tempski
parent 314ad2d877
commit 3673e4059b
3 changed files with 124 additions and 0 deletions
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25
examples/stm32/f4/stm32f4-discovery/tick_blink/Makefile Normal file
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##
## This file is part of the libopencm3 project.
##
## Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
##
## This library is free software: you can redistribute it and/or modify
## it under the terms of the GNU Lesser General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## This library 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 Lesser General Public License for more details.
##
## You should have received a copy of the GNU Lesser General Public License
## along with this library. If not, see <http://www.gnu.org/licenses/>.
##
BINARY = tick_blink
LDSCRIPT = ../stm32f4-discovery.ld
include ../../Makefile.include

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examples/stm32/f4/stm32f4-discovery/tick_blink/README Normal file
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README
------
This example is the same as fancy_blink except that it uses the
systick timer to generate time accurate delays. Shows how to set
up the systick timer to create an interrupt every millisecond and
how to write a delay routine (msleep) that can then delay for a
specific number of milliseconds.

91
examples/stm32/f4/stm32f4-discovery/tick_blink/tick_blink.c Normal file
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/*
* This file is part of the libopencm3 project.
*
* Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
* Copyright (C) 2011 Damjan Marion <damjan.marion@gmail.com>
* Copyright (C) 2011 Mark Panajotovic <marko@electrontube.org>
* Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
*
* This library is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
/* This version derived from fancy blink */
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/cm3/nvic.h>
#include <libopencm3/cm3/systick.h>
void msleep(uint32_t);
/* monotonically increasing number of milliseconds from reset
* overflows every 49 days if you're wondering
*/
volatile uint32_t system_millis;
/* Called when systick fires */
void sys_tick_handler(void) {
system_millis++;
}
/* sleep for delay milliseconds */
void msleep(uint32_t delay) {
uint32_t wake = system_millis + delay;
while (wake > system_millis) ;
}
/* Set up a timer to create 1mS ticks. */
static void systick_setup(void)
{
/* clock rate / 1000 to get 1mS interrupt rate */
systick_set_reload(168000);
systick_set_clocksource(STK_CTRL_CLKSOURCE_AHB);
systick_counter_enable();
/* this done last */
systick_interrupt_enable();
}
/* Set STM32 to 168 MHz. */
static void clock_setup(void)
{
rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
/* Enable GPIOD clock. */
rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
}
static void gpio_setup(void)
{
/* Set GPIO11-15 (in GPIO port D) to 'output push-pull'. */
gpio_mode_setup(GPIOD, GPIO_MODE_OUTPUT,
GPIO_PUPD_NONE, GPIO11 | GPIO12 | GPIO13 | GPIO14 | GPIO15);
}
int main(void)
{
clock_setup();
gpio_setup();
systick_setup();
/* Set two LEDs for wigwag effect when toggling. */
gpio_set(GPIOD, GPIO12 | GPIO14);
/* Blink the LEDs (PD12, PD13, PD14 and PD15) on the board. */
while (1) {
gpio_toggle(GPIOD, GPIO12 | GPIO13 | GPIO14 | GPIO15);
msleep(100);
}
return 0;
}