Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 509 of 547
NXP Semiconductors
UM10398
Chapter 28: LPC111x/LPC11Cxx Appendix: ARM Cortex-M0 reference
See Section 28–28.6.2.1 for more information about the access to the interrupt priority
array, which provides the software view of the interrupt priorities.
Find the IPR number and byte offset for interrupt M as follows:
• the corresponding IPR number, N, is given by N = N DIV 4
• the byte offset of the required Priority field in this register is M MOD 4, where:
– byte offset 0 refers to register bits[7:0]
– byte offset 1 refers to register bits[15:8]
– byte offset 2 refers to register bits[23:16]
– byte offset 3 refers to register bits[31:24].
28.6.2.7 Level-sensitive and pulse interrupts
The processor supports both level-sensitive and pulse interrupts. Pulse interrupts are also
described as edge-triggered interrupts.
A level-sensitive interrupt is held asserted until the peripheral deasserts the interrupt
signal. Typically this happens because the ISR accesses the peripheral, causing it to clear
the interrupt request. A pulse interrupt is an interrupt signal sampled synchronously on the
rising edge of the processor clock. To ensure the NVIC detects the interrupt, the
peripheral must assert the interrupt signal for at least one clock cycle, during which the
NVIC detects the pulse and latches the interrupt.
When the processor enters the ISR, it automatically removes the pending state from the
interrupt, see Section 28.6.2.7.1
. For a level-sensitive interrupt, if the signal is not
deasserted before the processor returns from the ISR, the interrupt becomes pending
again, and the processor must execute its ISR again. This means that the peripheral can
hold the interrupt signal asserted until it no longer needs servicing.
28.6.2.7.1 Hardware and software control of interrupts
The Cortex-M0 latches all interrupts. A peripheral interrupt becomes pending for one of
the following reasons:
• the NVIC detects that the interrupt signal is active and the corresponding interrupt is
not active
• the NVIC detects a rising edge on the interrupt signal
• software writes to the corresponding interrupt set-pending register bit, see
Section 28–28.6.2.4
.
A pending interrupt remains pending until one of the following:
• The processor enters the ISR for the interrupt. This changes the state of the interrupt
from pending to active. Then:
– For a level-sensitive interrupt, when the processor returns from the ISR, the NVIC
samples the interrupt signal. If the signal is asserted, the state of the interrupt
changes to pending, which might cause the processor to immediately re-enter the
ISR. Otherwise, the state of the interrupt changes to inactive.