Add possibility to setup Dma and max_transfer_size

[pyaillet]

Following the previous PRs, here is a proposition to enable configuration of max_transfer_size and Dma activation.

However, I am not satisfied with the content, because as said before if we use transfer_size > 64 without Dma it panics :\

Do you think max_transfer_size should be silently lowered when Dma is not used ?
Any idea of another to notify the user he's doing something wrong ?
Would some documentation on the method be enough ?

[ivmarkov]

Following the previous PRs, here is a proposition to enable configuration of max_transfer_size and Dma activation.

However, I am not satisfied with the content, because as said before if we use transfer_size > 64 without Dma it panics :\

Do you think max_transfer_size should be silently lowered when Dma is not used ? Any idea of another to notify the user he's doing something wrong ? Would some documentation on the method be enough ?

I would move max_transfer_size as a parameter of the Dma enum. I.e. all values except Disabled should have it. I would also implement a max_transfer_size() const fn method on the enum that returns 64 (or however the current value for non-dma transfer is calculated) for Dma::Disabled and min(max_transfer_size, 1440(?)) for all dma-enabled transfers in the enum. I would also do some checks in this method for when dma is enabled, like whether the number is divisible by 4, > 0 etc. and either round it down, or panic with a good message.

[pyaillet]

Thank you for the suggestions!

I applied most of them, though:

• I set the upper limit to 4096 (according to this) and confirmed it worked for me
• It seems min can't be called from a const fn