b50cdb56de
Update documentation and comments in code to reflect reality. Ensure that GPIO pin output speed is actually set, to ensure that 48Mhz sysclk output is functional. Actually set AF, instead of relying on reset values. Replace the systick code, the core of this example, with some code that has less traps and surprises. Instead of trying to get a direct interrupt x times per second, and reguarly running into problems with the 24 bit counter limit, use a method that triggers an interrupt every x ms instead. Tested MCO and blink rates with a logic analyser, properly verified working now :)
89 lines
2.5 KiB
C
89 lines
2.5 KiB
C
/*
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* This file is part of the libopencm3 project.
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*
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* Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
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* Copyright (C) 2013 Onno Kortmann <onno@gmx.net>
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* Copyright (C) 2013 Frantisek Burian <BuFran@seznam.cz> (merge)
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*
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* This library is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <libopencm3/stm32/rcc.h>
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#include <libopencm3/stm32/gpio.h>
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#include <libopencm3/cm3/nvic.h>
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#include <libopencm3/cm3/systick.h>
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/* Called when systick fires */
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void sys_tick_handler(void)
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{
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gpio_toggle(GPIOC, GPIO8);
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}
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/*
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* Set up timer to fire every x milliseconds
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* This is a unusual usage of systick, be very careful with the 24bit range
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* of the systick counter! You can range from 1 to 2796ms with this.
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*/
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static void systick_setup(int xms)
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{
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/* div8 per ST, stays compatible with M3/M4 parts, well done ST */
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systick_set_clocksource(STK_CSR_CLKSOURCE_EXT);
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/* clear counter so it starts right away */
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STK_CVR = 0;
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systick_set_reload(rcc_ahb_frequency / 8 / 1000 * xms);
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systick_counter_enable();
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systick_interrupt_enable();
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}
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/* set STM32 to clock by 48MHz from HSI oscillator */
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static void clock_setup(void)
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{
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rcc_clock_setup_in_hsi_out_48mhz();
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/* Enable clocks to the GPIO subsystems */
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rcc_periph_clock_enable(RCC_GPIOC);
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}
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static void gpio_setup(void)
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{
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/* Set blue led (PC8) as output */
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gpio_mode_setup(GPIOC, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO8);
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}
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static void mco_setup(void)
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{
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/* PA8 to AF 0 for MCO */
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rcc_periph_clock_enable(RCC_GPIOA);
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gpio_mode_setup(GPIOA, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO8);
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gpio_set_output_options(GPIOA, GPIO_OTYPE_PP, GPIO_OSPEED_100MHZ, GPIO8);
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gpio_set_af(GPIOA, 0, GPIO8);
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/* clock output on pin PA8 (allows checking with scope) */
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rcc_set_mco(RCC_CFGR_MCO_SYSCLK);
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}
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int main(void)
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{
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clock_setup();
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gpio_setup();
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mco_setup();
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/* 125ms ticks => 250ms period => 4Hz blinks */
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systick_setup(125);
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/* Do nothing in main loop */
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while (1);
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}
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