From 142636173e0bd15aa86c7372c7da2d16b431c6f0 Mon Sep 17 00:00:00 2001
From: David Harris <david_harris@hmc.edu>
Date: Sun, 24 Apr 2022 20:00:02 +0000
Subject: [PATCH] Added MTINST hardwired to 0, and added timeout of U-mode WFI

---
 pipelined/src/privileged/csrm.sv       | 2 ++
 pipelined/src/privileged/privileged.sv | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/pipelined/src/privileged/csrm.sv b/pipelined/src/privileged/csrm.sv
index 86171100c..2d306e4fe 100644
--- a/pipelined/src/privileged/csrm.sv
+++ b/pipelined/src/privileged/csrm.sv
@@ -52,6 +52,7 @@ module csrm #(parameter
     MCAUSE = 12'h342,
     MTVAL = 12'h343,
     MIP = 12'h344,
+    MTINST = 12'h34A,
     PMPCFG0 = 12'h3A0,
     // .. up to 15 more at consecutive addresses
     PMPADDR0 = 12'h3B0,
@@ -196,6 +197,7 @@ module csrm #(parameter
       MEPC:      CSRMReadValM = MEPC_REGW;
       MCAUSE:    CSRMReadValM = MCAUSE_REGW;
       MTVAL:     CSRMReadValM = MTVAL_REGW;
+      MTINST:    CSRMReadValM = 0; // implemented as trivial zero
       MCOUNTEREN:CSRMReadValM = {{(`XLEN-32){1'b0}}, MCOUNTEREN_REGW};
       MCOUNTINHIBIT:CSRMReadValM = {{(`XLEN-32){1'b0}}, MCOUNTINHIBIT_REGW};
 
diff --git a/pipelined/src/privileged/privileged.sv b/pipelined/src/privileged/privileged.sv
index 4aa9bf7c6..f75b21e67 100644
--- a/pipelined/src/privileged/privileged.sv
+++ b/pipelined/src/privileged/privileged.sv
@@ -139,7 +139,7 @@ module privileged (
     logic [`WFI_TIMEOUT_BIT:0] WFICount, WFICountPlus1;
     assign WFICountPlus1 = WFICount + 1;
     floprc #(`WFI_TIMEOUT_BIT+1) wficountreg(clk, reset, ~wfiM, WFICountPlus1, WFICount);  // count while in WFI
-    assign WFITimeoutM = STATUS_TW & PrivilegeModeW != `M_MODE & WFICount[`WFI_TIMEOUT_BIT]; 
+    assign WFITimeoutM = ((STATUS_TW & PrivilegeModeW != `M_MODE) | (`S_SUPPORTED & PrivilegeModeW == `U_MODE)) & WFICount[`WFI_TIMEOUT_BIT]; 
   end else assign WFITimeoutM = 0;
 
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