Interrupt Priority Preemption Bit Split Tool

Description

Split priority into preemption and subpriority using implementedBits - preemptionBits low bits for the latter.

A register mask selects bits within a fixed width. Read-clear and write-one-to-clear semantics describe state transitions that differ from ordinary assignment.

Split priority into preemption and subpriority using implementedBits - preemptionBits low bits for the latter.

When to use this tool

Use Interrupt Priority Preemption Bit Split when you need a deterministic fixed-width field or register-state calculation.

How to use the tool and how it works

Enter priority, implementedBits, preemptionBits. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read preemption, subpriority. Use the output convention below.

Split priority into preemption and subpriority using implementedBits - preemptionBits low bits for the latter.^[1]

Input field	Meaning and units	Accepted input
priority	Priority	Required. Safe integer; minimum 0.
implementedBits	Implemented Bits	Required. Safe integer; minimum 1; maximum 8.
preemptionBits	Preemption Bits	Required. Safe integer; minimum 0.

Output field	Interpretation	Returned shape
preemption	Preemption	Required. Safe integer.
subpriority	Subpriority	Required. Safe integer.

json

{
  "input": {
    "priority": 13,
    "implementedBits": 4,
    "preemptionBits": 2
  },
  "output": {
    "preemption": 3,
    "subpriority": 1
  }
}

Limitations and assumptions

Inputs are logical priority bits rather than a left-aligned register byte; the grouping and implemented width are supplied.
Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Use the device's access semantics and account for concurrent hardware changes before applying a register operation.

References

Calculation and input contract: microcontroller/interrupt-priority-preemption-bit-split — tool.io

Similar or alternative tools

NVIC Priority Field Left Shift
Left-align a logical priority with implementedBits in an eight-bit field by multiplying it by 2^(8 - implementedBits).
Interrupt Nesting Depth Margin
A lower numeric candidate preempts the last active priority; increase depth only when it would preempt and subtract from depthLimit for depthMargin.