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stm32: timer: further clarify example commentary

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The "timer" example is actually "the same" for both f1 and f4.  Do a
sanity sweep over the commentary, remove all vestiges that this was
cloned from a motor control example, and synchronize both examples.

Future work should extract the common portions "somewhere" but at least
make them consistent for now.
This commit is contained in:
Karl Palsson
2016-12-16 21:55:55 +00:00
parent da04ccdf71
commit d2abd471a5
1 changed files with 20 additions and 49 deletions
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65
examples/stm32/f4/stm32f4-discovery/timer/timer.c
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@@ -18,14 +18,18 @@
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
#include <libopencm3/cm3/nvic.h>
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/timer.h>
#include <libopencm3/cm3/nvic.h>
#include <libopencm3/stm32/exti.h>
#include <libopencmsis/core_cm3.h>
#ifndef ARRAY_LEN
#define ARRAY_LEN(array) (sizeof((array))/sizeof((array)[0]))
#endif
uint16_t frequency_sequence[18] = {
1000,
500,
@@ -80,75 +84,41 @@ static void tim_setup(void)
/* Enable TIM2 interrupt. */
nvic_enable_irq(NVIC_TIM2_IRQ);
/* Reset TIM2 peripheral. */
/* Reset TIM2 peripheral to defaults. */
rcc_periph_reset_pulse(RST_TIM2);
/* Timer global mode:
* - No divider
* - Alignment edge
* - Direction up
* (These are actually default values after reset above, so this call
* is strictly unnecessary, but demos the api for alternative settings)
*/
timer_set_mode(TIM2, TIM_CR1_CKD_CK_INT,
TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
/* Reset prescaler value.
* Running the clock at 10kHz.
*/
/*
* On STM32F4 the timers are not running directly from pure APB1 or
* APB2 clock busses. The APB1 and APB2 clocks used for timers might
* be the double of the APB1 and APB2 clocks. This depends on the
* setting in DCKCFGR register. By default the behaviour is the
* following: If the Prescaler APBx is greater than 1 the derived timer
* APBx clocks will be double of the original APBx frequencies. Only if
* the APBx prescaler is set to 1 the derived timer APBx will equal the
* original APBx frequencies.
*
* In our case here the APB1 is system frequency divided by 4 and APB2
* is system frequency divided by 2. This means APB1 timer will be 2 x
* APB1 and APB2 will be 2 x APB2. So when we try to calculate the
* prescaler value we have to use rcc_apb1_freqency * 2!!!
*
* For additional information see reference manual for the stm32f4
* familiy of chips. Page 204 and 213
* Please take note that the clock source for STM32F4 timers
* might not be the raw APB1/APB2 clocks. In various conditions they
* are doubled. See the Reference Manual for full details!
* In our case, TIM2 on APB1 is running at double frequency, so this
* sets the prescaler to have the timer run at 10kHz
*/
timer_set_prescaler(TIM2, ((rcc_apb1_frequency * 2) / 10000));
/* Disable preload. */
timer_disable_preload(TIM2);
/* Continous mode. */
timer_continuous_mode(TIM2);
/* Period (36kHz). */
/* count full range, as we'll update compare value continuously */
timer_set_period(TIM2, 65535);
/* Disable outputs. */
timer_disable_oc_output(TIM2, TIM_OC1);
timer_disable_oc_output(TIM2, TIM_OC2);
timer_disable_oc_output(TIM2, TIM_OC3);
timer_disable_oc_output(TIM2, TIM_OC4);
/* -- OC1 configuration -- */
/* Configure global mode of line 1. */
timer_disable_oc_clear(TIM2, TIM_OC1);
timer_disable_oc_preload(TIM2, TIM_OC1);
timer_set_oc_slow_mode(TIM2, TIM_OC1);
timer_set_oc_mode(TIM2, TIM_OC1, TIM_OCM_FROZEN);
/* Set the capture compare value for OC1. */
/* Set the initual output compare value for OC1. */
timer_set_oc_value(TIM2, TIM_OC1, 1000);
/* ---- */
/* ARR reload enable. */
timer_disable_preload(TIM2);
/* Counter enable. */
timer_enable_counter(TIM2);
/* Enable commutation interrupt. */
/* Enable Channel 1 compare interrupt to recalculate compare values */
timer_enable_irq(TIM2, TIM_DIER_CC1IE);
}
@@ -170,8 +140,9 @@ void tim2_isr(void)
new_time = compare_time + frequency;
timer_set_oc_value(TIM2, TIM_OC1, new_time);
if (frequency_sel == 18)
if (frequency_sel == ARRAY_LEN(frequency_sequence)) {
frequency_sel = 0;
}
/* Toggle LED to indicate compare event. */
gpio_toggle(GPIOD, GPIO12);