diff --git a/content/post/stm32-part0.md b/content/post/stm32-part0.md index 58b838a..17035c9 100644 --- a/content/post/stm32-part0.md +++ b/content/post/stm32-part0.md @@ -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) -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_) | +
Refer to the device datasheet for the frequency specifications and the power supply and load conditions for each speed
-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 +**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