Define hardware error exception cause code (#1105)

* Define hardware error and software check exception cause codes

* Add description of hardware error exception

src/hypervisor.adoc

@@ -339,6 +339,8 @@ causes (codes 16 and above).
 12 +
 13 +
 15 +
+18 +
+19 +
 20 +
 21 +
 22 +
@@ -358,6 +360,8 @@ Read-only 0 +
 Writable +
 Writable +
 Writable +
+Writable +
+Writable +
 Read-only 0 +
 Read-only 0 +
 Read-only 0 +
@@ -377,6 +381,8 @@ Environment call from M-mode +
 Instruction page fault +
 Load page fault +
 Store/AMO page fault +
+Software check +
+Hardware error +
 Instruction guest-page fault +
 Load guest-page fault +
 Virtual instruction +

src/machine.adoc

@@ -1711,7 +1711,10 @@ _Designated for platform use_
 13 +
 14 +
 15 +
-16-23 +
+16-17 +
+18 +
+19 +
+20-23 +
 24-31 +
 32-47 +
 48-63 +
@@ -1733,6 +1736,9 @@ Load page fault +
 _Reserved_ +
 Store/AMO page fault +
 _Reserved_ +
+Software check +
+Hardware error +
+_Reserved_ +
 _Designated for custom use_ +
 _Reserved_ +
 _Designated for custom use_ +
@@ -1807,6 +1813,17 @@ an instruction. Therefore, these exceptions have lower priority than
 other instruction address exceptions.
 ====
 
+[NOTE]
+====
+A Hardware Error is a synchronous exception triggered when corrupted or
+uncorrectable data is accessed explicitly or implicitly by an instruction.  In
+this context, "data" encompasses all types of information used within a RISC-V
+hart. The __x__epc CSR on delivery of the hardware error exception holds the
+address of the instruction that attempted to access corrupted data, while the
+__x__tval CSR is either set to 0 or holds the virtual address of an
+instruction fetch, load, or store that attempted to access corrupted data.
+====
+
 ==== Machine Trap Value Register (`mtval`)
 
 The `mtval` register is an MXLEN-bit read-write register formatted as

src/priv-preface.adoc

@@ -41,6 +41,7 @@ implemented.
 SXLEN≥UXLEN.
 * Clarified that WFI is not a HINT instruction.
 * Clarified ordering rules when PBMT=IO is used on main-memory regions.
+* Defined hardware error and software check exception codes.
 
 [.big]*_Preface to Version 20211203_*
 

src/supervisor.adoc

@@ -478,7 +478,10 @@ _Designated for platform use_
 13 +
 14 +
 15 +
-16-23 +
+16-17 +
+18 +
+19 +
+20-23 +
 24-31 +
 32-47 +
 48-63 +
@@ -499,6 +502,9 @@ Load page fault +
 _Reserved_ +
 Store/AMO page fault +
 _Reserved_ +
+Software check +
+Hardware error +
+_Reserved_ +
 _Designated for custom use_ +
 _Reserved_ +
 _Designated for custom use_ +