[sdiy] STM32MP1

[MTG]

Yikes. I think anyone in this business (making musical instruments or 
accessories) using a micro of any kind should have a pretty decent 
understanding of Real-Time Embedded Systems Programming.  A goldmine of 
information, examples, philosophies on this kind of thing can be found 
in the first decade of the print magazine, Embedded Systems Programming. 
I have a CD somewhere but heck if I can find it. Their series, "Inside a 
Real-Time Kernel" really changed *everything* for me.  I have a feeling 
the publisher has crushed the magazine content online because it's very 
hard to find.

Probably FreeRTOS has some great info too, but as I've never used it I 
can't say for sure. A quick glance shows this. And yes a lot of hardware 
choices, in and outside the CPU affect whether a system can be (hard-) 
real time.

"The scheduler in a Real Time Operating System (RTOS) is designed to 
provide a predictable (normally described as deterministic) execution 
pattern. This is particularly of interest to embedded systems as 
embedded systems often have real time requirements. A real time 
requirements is one that specifies that the embedded system must respond 
to a certain event within a strictly defined time (the deadline). A 
guarantee to meet real time requirements can only be made if the 
behaviour of the operating system's scheduler can be predicted (and is 
therefore deterministic).

Traditional real time schedulers, such as the scheduler used in 
FreeRTOS, achieve determinism by allowing the user to assign a priority 
to each thread of execution. The scheduler then uses the priority to 
know which thread of execution to run next. In FreeRTOS, a thread of 
execution is called a task."

https://www.freertos.org/about-RTOS.html