Add internal-clock feature

[maxkofler]

This feature allows to use the 'internal-clock' feature to define a lower clock speed.

[Rahix]

Hi, thanks for the contribution and sorry for the very late response...

This is an interesting idea, but I do wonder why you would need this? The boards have a crystal of the defined frequency, why would you not want to use it?

Is this about supporting the use of a bare microcontroller instead of an Arduino/SparkFun/etc. board? If yes, you should not be using arduino-hal in the first place - you should use atmega-hal directly (see #524).

[maxkofler]

Hi,

Basically, it is indeed about supporting bare microcontrollers, yes. The main reasoning behind this is that there are certainly some people that start out working with a fully integrated Arduino board for development but switch to a custom board or setup.

But as I see, there isn't that much interest in that feature, so I don't know about the importance of merging it.

[Rahix]

start out working with a fully integrated Arduino board for development but switch to a custom board or setup

Hmm, that is an interesting situation. In an ideal world, people would then rebase their application onto atmega-hal. But I know just as much as you do that most people won't...

My problem is that I don't really see what we can do about this:

• On one side, I really don't want to encourage the "wrong" behavior by providing things that make it easier. The right things to do should always be the path of least resistance.
• On the other side, it isn't really possible to make a switch from arduino-hal to atmega-hal simpler to perform. arduino-hal is supposed to hide some things from you by design, to allow quickly getting started with rust-on-arduino projects. These things need to be added manually when working with atmega-hal directly.

I guess the only thing that is left is providing much better documentation on how such a transition could be performed.

[maxkofler]

I totally agree with you in that people should rebase on atmega-hal, which is the obvious thing to do in my opinion, too.

After some thinking, I think, we should assume that once someone is on the level of building a custom board / circuit, he should be able to work with atmega-hal. Using the internal clocks on AVRs requires programming fuses, which requires some knowledge by itself, so one should be able to make the switch.

I do not want to force changes onto this project that make no sense, so I will abandon this PR.

[Rahix]

In any case, I've opened #532 for documenting these things.