Programming a DSP and a microcontroller on custom embedded hardware, using C and assembler language. Wrote the complete code for a DSP, from power-up and onwards, including framework, algorithms, integration and adaptation of third party libraries, et cetera, alone within less than 6 months.
Developing a test framework in the form of an emulation running in a Linux environment, thus opening the door tools otherwise not available like Valgrind, and repeatable offline tests for verifying correctness.
Was the sole developer the first year, being responsible for everything from specification to documentation and testing, then did knowledge transfer as new developers were recruited.