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The Interrupt Sources Window

To open the Interrupt Sources window, select the menu item Window > Show Interrupt Sources or press the key combination ⌘ + 4.

In a hierarchically structured table, the window indicates the list of all hardware units that send interrupt requests to the processor. For each source that sends interrupt signals, an abbreviated name and an internal identification number in hexadecimal representation are provided.

Abbreviations and numbers are defined by Apple and depend on the respective hardware model. We cannot provide a list of the abbreviations used by Apple at this point. In many cases, the names are self-explanatory, e.g. “wlan”, or they correspond to internal hardware units of the computer.

The window Interrupt Sources shows the list of hardware units that send interrupt requests to the processor.
The window Interrupt Sources shows the list of hardware units that send interrupt requests to the processor.

By clicking the disclosure triangle next to the name of each interrupt source, you can show or hide the readings if necessary. The column Counter indicates the type of measured value. Next to it, the concrete value is noted and the relative ratio compared to other counters of the same type is shown in the table via a bar graph.

Each incoming interrupt request is handled by a subroutine of the operating system kernel or another process. These subroutines are called interrupt handlers. For better processing, the handling is often divided into two subroutines of different hierarchical levels. Immediate processing takes place at level 1. If further post-processing is necessary to handle the signal, additional computations at level 2 will be carried out if necessary. This is shown in the column Counter by a corresponding indication Level x interrupt handler.

Depending on the type of interrupt processing, different details can be retrieved:

The durations per measurement time are given in the unit MATUs (Mach Absolute Time Units). This is a traditional time unit of the inner Mach system kernel of macOS. This time is measured by a counter that is increased by one in each nanosecond (billionth of a second). Under all conceivable operating conditions, it cannot always be guaranteed that the status of this counter corresponds to the actual status of wall-clock time. In practice, however, you can assume that 1 MATU = 1 ns = 0.000000001 s.

The indication “1,234 MATUs/s” thus corresponds to 0.000001234 seconds per second measurement time.