Hi all, I am currently working on a tock-registers redesign which: 1. Resolves the soundness issue <https://github.com/tock/tock-registers/issues/4> with register_structs. 2. Makes it relatively easy to unit-test driver implementations. Meeting these requirements without using procedural macros is not really feasible (the complexity of the required macro vastly exceeds the amount of complexity manageable in a macro_rules! macro). As a result, I plan to use procedural macros in tock-registers, and furthermore, those procedural macros will need to depend on the syn, quote, and proc-macro2 crates. I've opened PR 4814 <https://github.com/tock/tock/pull/4814> to extend Tock's external dependencies policy to allow for these macros. Please take a look at it and provide your input. Feedback has already resulted in one change: my tock-registers prototype now supports a build mode where macro expansion is performed up-front, allowing the procedural macros to be omitted from the final build. For reference, my current prototype for the new tock-registers is at tock-registers PR 11 <https://github.com/tock/tock-registers/pull/11>. Feel free to take a look at that and provide feedback on it as well! Thank you, Johnathan Van Why