nmi_exception.c File Reference

RA8D2 NMI handler – record the ICU cause instead of a bare trap. More...

#include <stdint.h>
#include "ra8_attributes.h"
#include "ra8_exception.h"
#include "ra8_icu_regs.h"

Include dependency graph for nmi_exception.c:

Go to the source code of this file.

Functions
static void	internal_nmi_report (const ra8_exception_frame_t *frame)
	Read the ICU NMI cause and hand off to the common fault record.
void	NMI_Handler (void)
	Cortex-M85 NMI handler (vector table slot 2).

Detailed Description

RA8D2 NMI handler – record the ICU cause instead of a bare trap.

Tag

[Ring 1 / Boot] {World: S}

The RA8D2 funnels its non-maskable interrupt sources through the ICU: IWDT/WDT underflow or refresh error, the PVD1/PVD2 voltage monitors, main/sub oscillation-stop detection, the NMI pin, bus errors, common/local memory (SRAM ECC) errors, CPU lockup, FPU exception, MRAM MRC/MRE read errors, and the inter-processor NMI. Which sources reach the core is chosen in NMIER; the latched cause lives in NMISR.

Historically every per-app vector_table.c weak-aliased NMI_Handler to Default_Handler – a bare bkpt + wfi trap – so the single most safety-relevant interrupt on the chip (the watchdog biting, an ECC error, a brown-out) produced zero diagnostics. The strong handler in this file overrides that weak alias tree-wide, exactly the way the shared SecureFault_Handler does:

1. A naked trampoline picks the stack pointer the NMI interrupted (MSP if EXC_RETURN[2] = 0, PSP otherwise) and tail-calls internal_nmi_report().
2. That reads the ICU NMISR cause register and forwards frame + cause into ra8_exception_report_nmi(), which snapshots both – plus the SCB diagnostics – into the fixed-SRAM g_ra8_exception_last record, best-effort logs them, and parks the CPU at a named halt symbol.

NMISR is deliberately NOT acknowledged (no NMICLR write): the handler never returns, and leaving the status latched preserves the evidence for a post-mortem debugger attach.

Copyright

Copyright (c) 2026 Brighton Sikarskie SPDX-License-Identifier: MIT

Definition in file nmi_exception.c.

Function Documentation

internal_nmi_report()

void internal_nmi_report ( const ra8_exception_frame_t * frame )

static

Read the ICU NMI cause and hand off to the common fault record.

Runs as the C half of the NMI trampoline below (external linkage is required for the asm tail-branch to name it). Reads NMISR exactly once and forwards it, with the interrupted context's stacked frame, into ra8_exception_report_nmi(). The register is read here – not in libs/ra8_core – because NMISR is an RA8D2 ICU register, outside the ARM-architectural scope of the core exception module.

Parameters

[in]

frame

Stacked exception frame the NMI entry pushed (selected MSP/PSP resident); forwarded verbatim.

Returns

Never returns.

Precondition

The Cortex-M85 has taken the NMI exception (IPSR == 2).

The ICU register block at 0x40006000 is accessible (always on).

Postcondition

g_ra8_exception_last carries exc_number 2 plus the NMISR cause.

Control never returns; the CPU halts at a named symbol.

Note

Not thread-safe (single NMI context by construction).

See also

ra8_exception_report_nmi() The recording + halt path.

Since

0.1.0

Definition at line 78 of file nmi_exception.c.

References ra8_exception_report_nmi(), and ra8_icu_nmisr().

NMI_Handler()

void NMI_Handler

(

void

)

Cortex-M85 NMI handler (vector table slot 2).

Strong definition overriding the weak NMI_Handler alias in every per-app vector_table.c. Naked trampoline in the exact shape of the HardFault/MemManage/BusFault/UsageFault/SecureFault trampolines: tst lr, #4 selects the interrupted stack (MSP when EXC_RETURN[2] = 0, else PSP) into r0 and control tail-branches into internal_nmi_report(), which appends the ICU cause. Naked asm is required: only assembly can read EXC_RETURN and the banked stack pointers before the compiler touches any register.

Precondition

The Cortex-M85 has taken the NMI exception.

The C runtime stack selected by EXC_RETURN[2] holds the frame.

Postcondition

Control transfers to internal_nmi_report() and never returns.

The interrupted context's frame pointer is in r0.

Note

Runs only in NMI context and is not thread-callable.

Since

0.1.0

Definition at line 109 of file nmi_exception.c.