Porting Firmware to a Domestic Cortex-M MCU: A Practical Migration Checklist

Second-sourcing the MCU is the single highest-leverage supply chain move an embedded team can make - and the one engineers resist most, usually because the last migration attempt turned into a three-month adventure. It does not have to be. On Cortex-M, the core is identical by contract; what differs is everything wrapped around it, and the differences follow a predictable checklist.

Before writing any code

• Pin and package mapping: parts like the Artery (雅特力) AT32F4xx series were designed with incumbent pinout compatibility in mind, but verify the full alternate-function table for your actual pins, not just the pin numbers. One remapped timer channel costs a board respin.
• Electrical margins: compare absolute maximum ratings, and the flash wait-state versus VDD table. A part that runs 0-wait at 3.3 V may need wait states at 2.7 V - sometimes a performance difference shows up only at the battery-end of the supply range.
• Memory sizing: match flash and SRAM with the linker map in hand, including the region reserved for the bootloader. Puya (普冉) PY32 M0+ class parts often pair smaller flash with better endurance; the swap is an opportunity to fix partition layout, not just a constraint.

The clock tree translation

This is where most migrations actually break. PLL multipliers, USB-critical 48 MHz paths, and the maximum-peripheral-clock rule differ between families even when the core speed matches. Walk the tree from crystal to every peripheral clock and re-derive the dividers; do not copy the incumbent values and hope. Then verify UART baud error at both ends of the temperature range, because an internally-generated clock source with slightly different tolerance shows up as framing errors on exactly one cold morning.

Peripheral differences that bite

• ADC: sampling time granularity, injected-channel trigger sources, and calibration routines differ. Budget a re-tune of the sampling time constants rather than copying them.
• Timers: complementary PWM and dead-time registers are conceptually identical across vendors, but the dead-time counter resolution may not be. Recalculate for the new timer clock.
• Boot behavior and option bytes: read protection, watchdog enable-on-reset, and boot pin latching are option-byte configured everywhere but written differently everywhere. This is also the moment to fix any unfortunate incumbent factory settings.
• Errata sheets: read the new part errata before the first board spins, not after the field returns. Domestic vendors publish these in English; the information density is comparable to incumbent documentation.

Toolchain and supply-side steps

Modern parts from AT32, PY32, and the Sinomcu (赛元) SC32F series are supported by GCC-based toolchains with vendor CMSIS packs, so the compiler move is usually the easy part. The two steps teams skip: first, re-run the timing-critical unit tests (motor control loops, communication state machines) on the new silicon at temperature, not just at desk conditions; second, agree the programming and debug tooling plan with production before the pilot run, because gang programmers and fixture pinouts are where schedule delays actually hide.

Done this way, a migration to a second MCU source is a two-to-four-week engineering task with a defined end: firmware builds, unit tests pass at temperature, production programming is verified, and the second supplier is real instead of theoretical. The checklist is not short, but every line on it is checkable - which is precisely what makes it short.