3.4.3. Fast IRQ interrupts

Fast IRQ mode is similar to IRQ mode, except that the highest-level IRQ interrupt handler assumes that no other IRQ interrupt occurs during its operation, and therefore, you do not require LR and SPSR. Table 3.25 lists the worst case cycles for fast IRQ interrupts.

Table 3.25. Fast IRQ interrupt latency

Event

Worst case (cycles)

Interrupt synchronization

3

Worst case interrupt disable period

10

Entry to first instruction

2

Load IRQ vector into PC

5

Total

20

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