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fixed typos, added new loader section for stm32part0

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Bastian de Byl
2019-12-12 10:34:34 -05:00
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content/post/stm32-part0.md
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@@ -1,8 +1,8 @@
---
title: "STM32F0 with libopencm3 Part 0: Simple GPIO"
title: "STM32F0 with libopencm3 - Part 0: Simple GPIO"
date: 2019-12-11
lastmod: 2019-12-11
tags: ["libopencm3", "stm32", "stm32f0", "tutorial"]
tags: ["libopencm3", "stm32", "tutorial"]
categories: ["Tutorial"]
contentCopyright: false
hideHeaderAndFooter: false
@@ -46,14 +46,14 @@ int main(void) {
# Getting Started with libopencm3
[libopencm3](https://github.com/libopencm3/libopencm3) is a very powerful,
useful, and open-source firmware library for the use in writing programs for
various different ARM Cortex-M microcontrollers. It's read me contains plenty of
useful, open-source firmware library for use in writing programs for various
different ARM Cortex-M microcontrollers. It's read me contains plenty of
information on the basics of getting started (typically done via `git
submodule`).
Additionally, there is a
[libopencm3-examples](https://github.com/libopencm3/libopencm3-examples)
repository to help get you started.
repository to help in getting started.
## Dependencies
@@ -89,6 +89,26 @@ my GitLab[^3].
To flash, it's as simple as `make flash` (_will also build the binary for your
convenience_).
## Loader
The loader (`.ld`) file is specific to the _flavor_ of ARM Cortex-M
microcontroller being used. Luckily, the authors of `libopencm3` provide example
loader files that can be used without any modification for your project
(_e.g. located in `libopencm3/lib/stm32/f0/` of the repo_).
## Project Structure
The Makefile, as of writing this, assumes your project directory structure has
`libopencm3` either cloned, copied, or initialized as a git submodule within the
same directory of your `main.c`. It is advised that you look through the
Makefile's variables of things you may want to change:
```
.
├── libopencm3
├── main.c
├── Makefile
└── stm32f0.ld
```
# Explanation
{{% admonition info "Naming Convention" %}}
@@ -110,7 +130,7 @@ The Discovery board comes with two LEDs for use by the user, tied to Port C pins
8 (blue LED), and 9 (green LED).
## Reset and Clock Control (RCC)
The **RCC**, and it's registers, are an important part _using_ the STM32
The **RCC**, and it's registers, are an important part in _using_ the STM32
microcontroller's peripherals. Luckily, utilizing `libopencm3` we can forego
bit-banging our way through each register's bits found in the reference
manual[^5] and simply utilize the GPIO port that we need -- in this case
@@ -141,8 +161,8 @@ authors, along with the function definition can be found
[**here**](https://libopencm3.org/docs/latest/stm32f0/html/group__rcc__defines.html#ga90aa2b7801b2b42debc0536d38c5b07c)</i></sub></center>
Having clarified that, wanting to drive the LEDs we will want to configure the
pins as outputs with no internal pull-up or pull-down resistor:
Having clarified that, as we want to **drive** the LEDs, we will need to
configure the pins as outputs with no internal pull-up or pull-down resistor:
```C
gpio_mode_setup(GPIOC, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO8);
gpio_mode_setup(GPIOC, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO9);
@@ -154,31 +174,32 @@ gpio_mode_setup(GPIOC, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO8 | GPIO9);
```
## GPIO Output Options Setup
Now that the GPIO mode has been set up, the output options need to be defined as
well. This will encompass the output type, and output speed:
Now that the GPIO mode has been set up, the GPIO output options need to be
defined as well. This will encompass the output type, and output speed:
| Output Type | Description |
|------------------|---------------------------------------------|
| `GPIO_OTYPER_PP` | (**default**) Push-pull "totem pole" output |
| `GPIO_OTYPER_OD` | Open-drain output |
| Output Speed | Description |
|----------------------|--------------------------------|
| `GPIO_OSPEED_HIGH` | High output speed |
| `GPIO_OSPEED_MED` | Medium output speed |
| `GPIO_OSPEED_LOW` | (**default**) Low output speed |
| `GPIO_OSPEED_100MHZ` | Up to 100MHz output speed |
| `GPIO_OSPEED_50MHZ` | Up to 50MHz output speed |
| `GPIO_OSPEED_25MHZ` | Up to 25MHz output speed |
| `GPIO_OSPEED_2MHZ` | Up to 2MHz output speed |
| Output Speed | Description |
|----------------------|---------------------------------------------------|
| `GPIO_OSPEED_HIGH` | High output speed |
| `GPIO_OSPEED_MED` | Medium output speed |
| `GPIO_OSPEED_LOW` | (**default**) Low output speed |
| `GPIO_OSPEED_100MHZ` | Up to 100MHz output speed (_equivalent to high_) |
| `GPIO_OSPEED_50MHZ` | Up to 50MHz output speed |
| `GPIO_OSPEED_25MHZ` | Up to 25MHz output speed (_equivalent to medium_) |
| `GPIO_OSPEED_2MHZ` | Up to 2MHz output speed (_equivalent to low_) |
<center><sub><i>Refer to the device datasheet for the frequency specifications
and the power supply and load conditions for each speed</i></sub></center>
As we'll be driving an output LED as opposed to sinking it (_typical
open-drain/open-collector sink configuration_), `GPIO_OTYPE_PP` will be
We'll be driving an output LED, as opposed to sinking it (_typical
open-drain/open-collector sink configuration_), push-pull output mode will be
required. Since there isn't any switching to be done aside from the initial
"on", we don't require _any_ speed -- though not being an option
`GPIO_OSPEED_LOW` should suffice:
"on", we don't require _any_ "speed" -- "no speed" not being an option
`GPIO_OSPEED_LOW` will suffice:
```C
gpio_set_output_options(GPIOC, GPIO_OTYPE_PP, GPIO_OSPEED_LOW, GPIO8);
@@ -192,7 +213,7 @@ gpio_set_output_options(GPIOC, GPIO_OTYPE_PP, GPIO_OSPEED_LOW, GPIO8 | GPIO9);
## Turn it on!
There are no additional options required for the user to be able to now set, or
clear, the desired GPIO pins so we simple set it _and forget it_:
clear, the desired GPIO pins. Thus, we set it _and forget it_:
```C
gpio_set(GPIOC, GPIO8);
@@ -204,8 +225,6 @@ _Simplified[^6]:_
gpio_set(GPIOC, GPIO8 | GPIO9);
```
**Voila!**
Lastly, we need to make sure our program never **exits** and does something
_undesirable_ by keeping it inside a loop:
```C
@@ -224,6 +243,8 @@ while(1) {
C -
Explained](http://www.learningaboutelectronics.com/Articles/While-(1)-embedded-C.php) article</i></sub></center>
**Voila!**
[^1]: [GNU Arm Embedded Toolchain](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm)
[^2]: [Makefile](https://gitlab.com/bdebyl/stm32f0-example-project/blob/b858d5e38026bcce3b8aad4085ffb665ddf63eef/Makefile) as of writing this post
[^3]: https://gitlab.com/bdebyl