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Added new clocks approach #159
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It seems like the current system fails silently, and gives the user too many degrees of freedom. Eg the illusion you can set whatever speeds you want. I think the STM32Cube IDE visual clock config is a good guide for what configs are valid.
Suggestion: Instead of setting speeds, set the various scalers. This alone reduces the degrees of freedom. Have a helper method to show what speeds these output. Calculate the speeds, and validate before setting. This deals with errors in 2 ways: Prevents requesting speed combinations that can't be set using the scalers and 2: Fails explicitly if the resulting speeds are out of range.
Example use:
See
examples/clocks.rs
for more sytnax.Stated another way: With this new approach, you only need to validate that the resulting speeds are within defined ranges. With the existing approach, you're solving a system of equations that may have 0, 1, or multiple solutions. The current API doesn't seem robust enough to handle the 0 and multiple cases, and I think it might be easier to change approaches, than create a robust solver.
We can mitigate the more abstract nature of setting scalers by including sensible defaults. I've added a
default::Default
impl, but we could add several alternatives.In summary, this is a big departure from the existing approach. Here's why I think it's worth it:
Challenge: Can you successfully set a 72Mhz sysclk using the existing module? I've been unable, but can using the example above.