Platforms

One Bazel target platform per STM32 family (:stm32f0, :stm32f4, :stm32g4, :stm32h7). Each is arm + os:none plus an :mcu_core constraint (cortex_m0 / cortex_m4f / cortex_m7f) that selects the matching //toolchains variant, where the family's -mcpu/-mfpu/-mfloat-abi live.

mcu_core is a custom constraint setting because @platforms//cpu is too coarse: cortex-m4f and cortex-m7f are both armv7e-m with hard float, yet need different -mcpu/-mfpu flags.

Nobody passes --platforms by hand: firmware_project transitions each board to its family's platform automatically (see tools/firmware).

Adding a family

1. If it's a new CPU core, add the constraint_value here and a toolchain variant in //toolchains.
2. Add the platform here with that core constraint.
3. Map the family in FAMILY_PLATFORMS (//tools/firmware:firmware_project.bzl) and package its HAL in //drivers/stm32.