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641 interrupt priority values discrepancy between major and external interrupts #668

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641 interrupt priority values discrepancy between major and external interrupts #668

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fd02f09
Smnip: Fixing typo
christian-herber-nxp Dec 9, 2025
05f501f
ACLIC: Fixing typos in description of interrupt delivery
christian-herber-nxp Dec 9, 2025
9283293
Smnip: Clarifying operation of global threshold
christian-herber-nxp Dec 9, 2025
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16 changes: 12 additions & 4 deletions src/aclic.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -284,8 +284,8 @@ External interrupt signals are supplied to the hart from the respective domain.
The interrupts from the root domain appear as MEIP (Machine External Interrupt-Pending),
and interrupts from the child domain appear as SEIP (Supervisor External Interrupt-Pending).

In addition to signalling a pending interrupt,
a hart-local APLIC domain singals the priority and identity of the highest priority pending-enabled interrupt to the hart.
In addition to signaling a pending interrupt,
a hart-local APLIC domain signals the priority and identity of the highest priority pending-enabled interrupt to the hart.
This information is accessible at the hart through the {xtopei} CSR.

=== Interrupt domain control interface (Smidctrl, Ssidctrl)
Expand Down Expand Up @@ -738,13 +738,21 @@ The reset behavior of other fields is platform-specific.
=== Operation

When {xithreshold} is a nonzero value,
an interrupt sources _i_ at with priority number `iprio[i]`
an interrupt source _i_ with priority number `iprio[i]`
is considered disabled irrespective of its interrupt-enable bit,
when the following condition holds:

[source]
----
iprio[i] >= xithreshold & NIPPRIO_MASK
IPRIO >= xithreshold & NIPPRIO_MASK

where IPRIO is equivalent to the value reported in xtopi CSR, i.e.

1 < iprio[i] <= 255: IPRIO = iprio[i]
255 < iprio[i]: IPRIO = 255
iprio[i] = 0:
default priority higher than a machine external interrupt: IPRIO = 0
default priority lower than a machine external interrupt: IPRIO = 255
----

When {xithreshold} is zero,
Expand Down