With the dense codebase that you have and the lack of knowledge regarding the IDE or compiler it was built with, I truly understand the pressing need for an STM32 expert who can hit the ground running. Luckily, dissecting complex firmware issues is a forte of mine and the STM32 microcontroller is my playground. I'm Luis Enrique with E-Lance Tec and my team and I are adept at running and testing STM32 code, as well as migrating it to different setups like STM32CubeIDE for optimal performance.
I have had extensive experience in working with registers directly for handling real-time tasks, such as your project requires. I am experienced enough to avoid using HAL Library that, as you mentioned, may sometimes delay code execution. My proficiency goes beyond just dealing with STM32s - encompassing knowledge and skills in various other dialects such as C/C++, Java, Python, Micropython, Circuitpython, ARM Cortex-M, Atmel, and PIC. This profound flexibility helps me bring innovative solutions that are not limited to just one framework.