From 10700d0766501c9a4ce16c7cab53c908c44d5158 Mon Sep 17 00:00:00 2001 From: Andrew Waterman Date: Tue, 20 Feb 2024 18:07:55 -0800 Subject: Update Smrnmi to account for Smdbltrp extension This is a backwards compatible change to support resumable double traps within M-mode when both extensions are implemented. Although the resumability feature is not terribly interesting, the reuse of the Smrnmi state for M-mode double traps aids debugging (and fault diagnosis for the hardware-error exception case). --- src/rnmi.adoc | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) (limited to 'src/rnmi.adoc') diff --git a/src/rnmi.adoc b/src/rnmi.adoc index 9938917..cbd19da 100644 --- a/src/rnmi.adoc +++ b/src/rnmi.adoc @@ -71,9 +71,15 @@ of holding. .Resumable NMI cause `mncause`. include::images/bytefield/mncause.edn[] -The `mncause` CSR holds the reason for the NMI, with bit MXLEN-1 set to -1, and the NMI cause encoded in the least-significant bits or zero if -NMI causes are not supported. +The `mncause` CSR holds the reason for the NMI. +If the reason is an interrupt, bit MXLEN-1 is set to 1, and the NMI +cause is encoded in the least-significant bits. +If the reason is an interrupt and NMI causes are not supported, bit MXLEN-1 is +set to 1, and zero is written to the least-significant bits. +If the reason is an exception within M-mode that results in a double trap as +specified in the Smdbltrp extension, bit MXLEN-1 is set to 0 and the +least-significant bits are set to the cause code corresponding to the +exception that precipitated the double trap. .Resumable NMI status register `mnstatus`. include::images/bytefield/mnstatus.edn[] -- cgit v1.1