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Interrupt Latency Calculator

Work out interrupt latency instantly with clear inputs, formula shown and shareable results.

About Interrupt Latency Calculator

Worst-case interrupt latency is hardware entry time plus the longest uninterruptible instruction plus the longest section where interrupts are disabled. That last term is usually the dominant one and is entirely under the programmer's control, which is why critical sections must be kept short.

Formula

Interrupt latency

latency = (entry cycles + longest instruction + longest disabled section) / clock frequency

Worked example

With the default values below, Interrupt Latency Calculator returns Worst-case latency of 0.83. Change any input above and every figure here is recalculated in your browser.

Inputs used

Clock frequency
72 MHz
Interrupt entry cycles
12 cycles
Longest uninterruptible instruction
8 cycles
Longest interrupts-disabled section
40 cycles

Results

Worst-case latency
0.83 µs
Hardware entry time
0.17 µs
Blocking from critical sections
0.67 µs
Maximum sustainable interrupt rate
120.00 kHz

Step by step

  1. 1Values used
  2. 2Interrupt latency
  3. 3Worst-case latency= 0.83 µs
  4. 4Hardware entry time= 0.17 µs
  5. 5Blocking from critical sections= 0.67 µs
  6. 6Maximum sustainable interrupt rate= 120.00 kHz

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is the critical section usually worst?

Hardware entry is a dozen cycles, but a poorly written disabled section — a loop, a division, a long copy — can be thousands, and it delays every interrupt in the system.

What is priority inversion in this context?

A low-priority handler that runs long or disables interrupts delays a high-priority event, defeating the priority scheme entirely.

Related Calculators

Interrupt Latency Calculator – Calculate Worst-case latency