116 lines
3.9 KiB
Markdown
116 lines
3.9 KiB
Markdown
---
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title: "STM32F0 with libopencm3 - Part 1: Simple Timer"
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date: 2020-02-12
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lastmod: 2020-02-12
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draft: true
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tags: ["libopencm3", "stm32", "tutorial"]
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categories: ["Tutorial"]
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contentCopyright: false
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hideHeaderAndFooter: false
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---
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After having reviewed [**Part 0**](/post/stm32-part0) of this series, we can now
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explore controlling GPIO with the hardware timers! Other tutorials have used the
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Systick timer as a good introduction to adding a delay for blinking an
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LED. However, it is my belief that this leads to confusion for beginners and
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only opens the door to misunderstandings. That being said, we will be using
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timers and their associated GPIO ports with Alternate Function modes.
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<!--more-->
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# Straight to the Chase
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For those that want to cut to the chase and save time, here is the full source
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code with friendly names to get you started:
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{{< admonition note "Source Code" true >}}
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```C
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#include <libopencm3/stm32/gpio.h>
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#include <libopencm3/stm32/rcc.h>
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#include <libopencm3/stm32/timer.h>
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#define LED_PORT GPIOC
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#define LED_PIN_BLU GPIO8
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#define LED_PIN_GRN GPIO9
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#define TIM_PSC_DIV 48000
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#define SECONDS 1
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volatile unsigned int i;
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int main(void) {
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rcc_clock_setup_in_hsi_out_48mhz();
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rcc_periph_clock_enable(RCC_GPIOC);
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rcc_periph_clock_enable(RCC_TIM3);
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gpio_mode_setup(LED_PORT, GPIO_MODE_AF, GPIO_PUPD_NONE, LED_PIN_BLU | LED_PIN_GRN);
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gpio_set_output_options(LED_PORT, GPIO_OTYPE_PP, GPIO_OSPEED_HIGH, LED_PIN_BLU | LED_PIN_GRN);
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gpio_set_af(LED_PORT, GPIO_AF0, LED_PIN_BLU | LED_PIN_GRN);
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timer_set_mode(TIM3, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_CENTER_1, TIM_CR1_DIR_UP);
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// The math for seconds isn't quite right here
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timer_set_prescaler(TIM3, (rcc_apb1_frequency/TIM_PSC_DIV)/2*SECONDS);
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timer_disable_preload(TIM3);
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timer_continuous_mode(TIM3);
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timer_set_period(TIM3, TIM_PSC_DIV);
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timer_set_oc_mode(TIM3, TIM_OC3, TIM_OCM_PWM1);
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timer_set_oc_mode(TIM3, TIM_OC4, TIM_OCM_PWM2);
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int tim_oc_ids[2] = { TIM_OC3, TIM_OC4 };
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for (i = 0; i < (sizeof(tim_oc_ids)/sizeof(tim_oc_ids[0])); ++i) {
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timer_set_oc_value(TIM3, tim_oc_ids[i], (TIM_PSC_DIV/2));
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}
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timer_enable_oc_output(TIM3, TIM_OC3);
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timer_enable_oc_output(TIM3, TIM_OC4);
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timer_enable_counter(TIM3);
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while (1) {
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;
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}
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return 0;
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}
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```
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{{< /admonition >}}
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# Set up the GPIO
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Assuming the reader is either familiar with GPIO setup for the STM32F0, or has
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reviewed [**Part 0**](/post/stm32-part0) of this series we will set up the GPIO
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pins tied to the LEDs (_port C, pins 8 and 9_) in the Alternate Function mode.
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## Alternate Functions
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The STM32 microcontroller's GPIO has a hardware feature allowing you to tie
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certain port's pins to a different register as part of the output or input
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control:
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{{< img src="/static/img/stm32-examples/part1/stm32-af-diagram.png"
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sub="GPIO Alternate Function Diagram" >}}
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For accomplishing this, a few things need to happen:
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1. The desired GPIO pins need to be set to `GPIO_MODE_AF` in `gpio_mode_setup()`
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1. The alternate function mode number `GPIO_AFx` has to be set for the pins using `gpio_set_af()`
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{{< admonition warning "Note for Different STM32Fx Microcontrollers" >}}
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Review the datasheet for the specific **STM32Fx** microcontroller being
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programmed, as the Alternate Function mappings may be *significantly* different!
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{{< /admonition >}}
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## GPIO Alternate Function Setup
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For the STM32F0 we are using in this series, the Alternate Function selection
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number desired is `GPIO_AF0` for use with `TIM3_CH3` (_timer 3, channel 3_) and
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`TIM3_CH4` (_timer 3, channel 4_):
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{{< img src="/static/img/stm32-examples/part1/stm32-af-gpiomap.png"
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sub="STM32F051 Alternate Function Mapping" >}}
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Ultimately, the code with `libopencm3` becomes the following for our use case:
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```C
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gpio_mode_setup(GPIOC, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO8 | GPIO9);
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gpio_set_output_options(GPIOC, GPIO_OTYPE_PP, GPIO_OSPEED_HIGH, GPIO8 | GPIO9);
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gpio_set_af(GPIOC, GPIO_AF0, GPIO8 | GPIO9);
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```
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