1. Scheduler Hardening and Task Discovery

Spent part of this session making the RTOS scheduler itself more robust. I added a findTaskByName() function so interrupt-driven task lookups happen dynamically instead of relying on hardcoded task indices, which was a fragile setup just waiting to break the moment task registration order changed. Alongside that, I wrapped every one of those lookups with lambdas that throw a proper warning if a task can’t be found, so a missing task fails loudly instead of silently dereferencing a null pointer somewhere downstream.

2. Blocking vs Non-Blocking Scheduled Tasks

After a lot of painful debugging, I traced a string of issues (including interrupt tasks silently failing to fire and scheduled tasks stepping on each other) back to non-blocking statements I’d introduced inside scheduled tasks in the previous devlog. I ended up taking those out and reverting scheduled tasks fully back to blocking, which is genuinely what the scheduled zone was designed for in the first place: tasks that don’t need to run in polynomial time and can safely block without putting the drone at risk of crashing. Once that was sorted, I converted the raw USART byte-pushing into a blocking DMA system instead, so streaming is handled by DMA hardware rather than manually pushed byte-by-byte over USART.

3. Flight Loop Refactor and VTX Communication

On the flight logic side, I refactored flightLoop() to use lambdas and a state machine so I would never have to yield in the middle of my tasks (which was used previousely for zeroing motor outputs). I also converted the error handling into a proper state machine, so different types of warnings can be caught and handled distinctly instead of lumping every issue into one path, and turned on full debug printing whenever the system is running. Last but not least, I built out a dedicated injector for respondToVTX so I can properly test and simulate VTX communication going forward.

4. Real Hardware Testing

Since, I am almost 100% done with the RTOS I bought two NUCLEO-F756ZG’s which will serve as testing the 100% production code rather than the simulation version. I bought two so that one of the boards will be running the real RTOS code, testing DMA reading from USART, SPI, and emitting real motor signals, while the second will be emulating all of my peripherals. When the boards come, if the code does work, it will also mean that the real PCB’s will also work when my friend finishes with them.

5. Next Steps

As of now there are a few issues with the double preempt system (for the interrupt tasks) I designed a while back, so I will need to debug that before they arrive. Right now before the boards arrive, I will be finishing up the RTOS blocking DMA pipelines (stripping out IRQ, removing NVIC etc. for scheduled tasks), and performing a bunch of baseline testing in order to prove that the RTOS is capable of flying an actual drone!