A way to specify memory properties like flash size

[bjoernQ]

It's very convenient that we don't need a memory.x or build.rs in binary crates using the HAL

However, we should be able to set things like flash size if it doesn't match our default.

Ideally not by providing custom linker scripts

[MabezDev]

Perhaps a somewhat odd but simple strategy, what about setting the flash size to the addressable per chip and then letting the flashing step detect the failures?

E.g for the esp32 the max external flash supported is 16MB, we'd set that in the linker script. If someone tried to flash a 12MB program on a physical module with only 4MB the flashing step will fail.

[bjoernQ]

Maybe flash size was not the best example. What about things like guaranteed allocated stack-size (which are not manageable in a sane way with cargo features)

[bjoernQ]

I tried https://crates.io/crates/toml-cfg and it seems to work great for this use-case. It works in the library code and in build.rs

I guess we could just use it as is, however there are a few things I don't like that much (for our use-case)

• the sections in the cfg.toml need to match the pkg-name of the library, so users would need to have sections like esp-hal-common and esp32c3-hal etc. - would be better to have something like esp-hal or maybe don't needing a namespace at all
• would be better to have some other name than cfg.toml for the configuration file (e.g. esp-hal.cfg or esp-hal-cfg.toml)

Maybe we could just pick-up the idea of toml-cfg and have our own macro (in esp-hal-procmacros)

[MabezDev]

Another option might be to use cargo's built-in [env] section. This might get a bit long if we have a lot of tunables though.

[MabezDev]

I think this is a duplicate of #1111, so lets continue the discussion there.