Porting Legacy Firmware to a Modern Microcontroller
Porting a legacy assembly firmware to C on a modern microcontroller, creating a maintainable and future-proof platform.
Our client had a long-established product built around a Microchip PIC microcontroller and a firmware written entirely in assembly language. While the system was proven and reliable, it had reached a point where further development was impractical. The limited resources of the MCU and the complexity of the legacy codebase made it difficult to add new features or adapt the product to future needs.
We were asked to modernise the platform by porting the firmware into a maintainable C codebase and introducing support for a more capable, pin-compatible microcontroller.
Challenge
Our client wanted to extend their product with new software features. However, this was not feasible on the ageing PIC MCU, which had limited memory and processing resources, nor on the existing assembly-language codebase, which made ongoing development difficult.
The challenge was twofold: to reimplement the codebase in a more maintainable language, and to identify a suitable replacement MCU with the capacity to support future enhancements.
Project Overview
This work was delivered as a continuation of an earlier project, where we reverse-engineered a legacy firmware written in assembly language, and produced clear design documentation while updating the software to work with modern development tools.
That initial phase created the technical understanding and documentation needed to safely reimplement the firmware in C and migrate to a more capable microcontroller.
Read Part 1 of this project: Updating the software for upcoming improvements.
Action
We reimplemented the full functionality in C, carefully abstracting processor-specific elements from the system behaviour. The rewrite was first completed on the original hardware, enabling structured side-by-side testing against the original assembly firmware. This ensured functional equivalence while avoiding the new hardware variables during the verification stage.
Once the C implementation was validated, we selected a pin-compatible MCU with increased FLASH, RAM, and improved peripherals. Thanks to the abstracted design, porting to the new device was straightforward. Rigorous testing was then carried out using the updated hardware platform.
OUTCOME
The client now benefits from a maintainable C codebase running on a modern MCU platform, providing immediate performance improvements and a solid foundation for adding new software features that will enhance the product’s value in future.
This approach also reduced project risk by validating the new code on the original hardware first, ensuring continuity before moving to the new device. The abstraction we introduced makes the firmware easier to maintain and extend, lowering long-term development costs. Most importantly, the client now has a future-proof platform that gives them the flexibility to evolve their product in line with customer needs.
TECHNOLOGIES & SERVICES INVOLVED
- Microchip PIC
- Embedded firmware (Assembly & C Language)
Software, Consumer
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