2.6. Operating modes

In all states there are seven modes of operation:

Modes other than User mode are collectively known as privileged modes. Privileged modes are used to service interrupts or exceptions, or to access protected resources.

Each register has an operating mode as shown in Table 2.1.

Table 2.1. Register mode identifiers

Mode

Mode identifier

User

usr[1]

Fast interrupt

fiq

Interrupt

irq

Supervisor

svc

Abort

abt

System

usra

Undefined

und

[1] The usr identifier is usually omitted from register names. It is only used in descriptions where the User or System mode register is specifically accessed from another operating mode.

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