Export FmcSdramConfiguration and FmcSdramTiming structs

[glindstedt]

This allows implementing SdramChip outside of this crate.

This is useful when implementing a new device. Projects depending on this crate would not have to depend on a fork while waiting for a PR to be merged with the new device.

It would also make it much easier implementing a new device when depending on a HAL crate. In my case I was depending on stm32h7xx-hal (which depends on stm32-fmc) as well as depending on a local version of stm32-fmc with a new device implementation. This caused the issue described here: rust-lang/rust#22750. Not being able to implement SdramChip outside of the crate would force me to maintain forks of both stm32-fmc as well as stm32h7xx-hal until 1) stm32-fmc merges a PR, and 2) stm32h7xx-hal would adopt the new release.

I'm not sure if the structs were ever meant to be exposed, but I think having some way to implement the SdramChip trait outside of this crate would be really helpful.

[glindstedt]

Found a small workaround for my issue, which is to use a [patch] section as described here https://doc.rust-lang.org/cargo/reference/overriding-dependencies.html#the-patch-section.

However, I still think it would be useful to be able to implement the trait outside the crate.

[richardeoin]

Thanks! Agreed that exporting these is correct. Actually the naming is a bit confusing also, perhaps this is a good time to rename them to SdramConfiguration and SdramTiming? The Fmc prefix makes me think they come from fmc.rs (where they would have been exported).

It would also be useful to add a new test for implementing SdramChip outside the crate, so this doesn't get forgotten again.

Once this PR is merged I can make a patch release (0.2.1) which will be automatically used by stm32h7xx-hal after running cargo clean/rm Cargo.lock (the hal has a caret requirement). Whilst developing the [patch] section is the correct solution, a note about that could be added to README.md / DEVELOPING.md to help others who don't know about it.

[glindstedt]

I've implemented what you suggested. For the test I just copied the existing sdram_pins_12a_4b test but used the DummyChip device (which has the configuration from is42s32800g_6). I believe just using it in the Sdram::new() method is enough to ensure that the trait is properly implemented.

[richardeoin]

Awesome, looks good to me

[richardeoin]

v0.2.1 released https://crates.io/crates/stm32-fmc

[glindstedt]

Thanks! 👍