Unisys - 1989 -> 1991
Convergent Technologies hired me out of college. What I didn't know was that they were just purchased by Unisys Corporation. Happily, the Convergent spirit remained during my employ.
Initially, I ported several Unix utilities to the CTOS platform. The difficulty in porting these utilities was the lack of any IDE for testing and debugging. The Unix utilities were written in C but I had to de-bug in 8088 assembly.
As a learning excercise, I created a system-service which enhanced the CTOS operating system by adding environment variables (which previously weren't available.) This work directly led to the porting of Microsoft's C compiler to CTOS.
I then ported the XVT cross-platform development environment to CTOS. This task involved writing several sub-system drivers (mouse, keyboard, video, printer, file-system, etc.) with which XVT could communicate. Once again, XVT code and the drivers were written in C but all debugging was done at the assembly language level.