Operating System Notes

These are miscellaneous useful notes about how ChibiOS functions.

Stacks Configuration

From ChibiOS crt0.c:

Two stacks available for Cortex-M, main stack or process stack.

• Thread mode: Used to execute application software. The processor enters Thread mode when it comes out of reset.
• Handler mode: Used to handle exceptions. The processor returns to Thread mode when it has finished all exception processing.

ChibiOS configures the Cortex-M in dual-stack mode. (CONTROL[1]=1) When CONTROL[1]=1, PSP is used when the processor is in Thread mode.

MSP is always used when the processor is in Handler mode.

• main_stack_size: Used for exception handlers. Yes, really.
• process_stack_size: Used by main().

After chSysInit(), the current instructions stream (usually main()) becomes the main thread.