RP series

RP chip such as RP2040 and RP2350 is used by microcontroller such as ProMicro RP2040.

RP2040 and CAS

When compiling rktk for RP2040, you may see errors related to Atomic. This is because RP2040 has old architecture (thumbv6) and this architecture does not support feature called atomic CAS.

Fortunately, polyfill for such old architecture is provided by portable-atomic. But to use this, you have to manually add portable-atomic as dependency with unsafe-assume-single-core or critical-section feature.

Usually, unsafe-assume-single-core should be OK as rktk does not use multiple core. Although, if you have other dependencies that utilize multiple core, you have to use critical-section feature instead.