Technical mental model
SysTick is often the timing backbone of scheduler and timeout logic. Correct tick configuration requires explicit math and awareness of ISR overhead.
Key low-level points:
- Tick period is determined by clock source and reload value.
- Short tick periods improve resolution but increase CPU overhead.
- Tick handlers should do minimal work and signal deferred processing paths.
Equations and constraints that drive decisions
Reload register setup:
Where:
- : SysTick clock frequency
- : desired tick frequency
Tick period:
Implementation walkthrough
Pick tick frequency from latency target and CPU budget, not arbitrary defaults.
Validate reload values against clock configuration after PLL/source changes.
Keep ISR constant-time and move variable-cost work outside handler.
Test drift and jitter with real hardware measurements.
Validation and debugging checklist
Off-by-one reload mistakes create persistent timing drift.
High-frequency ticks with heavy handlers waste significant CPU.
Runtime clock changes can silently invalidate tick assumptions.
Timeout arithmetic must handle wraparound correctly.
Good SysTick design combines correct math with disciplined ISR scope and runtime timing verification.
