RFC: Automatic clock configuration #48
Description
The HAL currently expects the user to manually select a suitable clock configuration. Usually, this is done using, for example, STM32CubeMX.
I would argue that this is not what most users want - they do not want to download a comparably large additional software package and click through its interface whenever their clock requirements change. I would argue that it should be possible to specify the required frequencies somewhere in the project and have some tool automatically generate the required clock configuration.
Other HALs (stm32f4xx-hal, for example) implement a more comfortable interface which calculates the PLL configurations at runtime. This approach is suboptimal as it increases code size and startup time - clock configuration calculation should ideally be done at compile time.
I just hacked a library together (mgottschlag/stm32g4xx-clkcfg) together which basically performs an exhaustive search over all possible clock configurations, selecting the best according to the requirements specified by the user. The library then generates a code fragment that can be included via include!().
What do you think of this approach? Should something like that be integrated into the HAL or at least referenced by the README?
Currently, the library has its own copy of stm32g4xx-hals config structs and will therefore break whenever those are changed, so some refactoring is necessary to make the approach more robust.
Usage Example
use std::io::stdout;
use embedded_time::rate::*;
use stm32g4xx_clkcfg::{ClockRequirements, Frequencies};
fn main() {
println!("Configuration for the highest possible sysclk with a 48MHz USB clock from a 24 MHz crystal:");
let req = ClockRequirements::new()
.hse(24_000_000.Hz())
.sysclk(170_000_000.Hz())
.usb_rng_clk(true);
match req.resolve(false) {
Ok((cfg, freqs)) => {
cfg.write_code(&mut stdout()).unwrap();
// _freqs holds the frequencies generated by the configuration.
}
Err(e) => {
println!("Error: {:?}", e);
}
}
}