WIRI/WPRI fields should be hardwired to 0 (#121)

1 files changed, 8 insertions, 4 deletions

diff --git a/src/priv-csrs.tex b/src/priv-csrs.tex
index e13e96a..003f5df 100644
--- a/src/priv-csrs.tex
+++ b/src/priv-csrs.tex
@@ -374,16 +374,20 @@ Some read-only and read/write registers have read-only fields reserved
 for future use.  These reserved read-only fields should be ignored on
 a read.  Writes to these fields have no effect, unless the whole CSR
 is read-only, in which case writes might raise an illegal instruction
-exception. These fields are labeled \wiri\ in the register
-descriptions.
+exception.
+For forward compatibility, implementations that do not furnish these fields
+must hardwire them to zero.
+These fields are labeled \wiri\ in the register descriptions.
 
 \subsection*{Reserved Writes Preserve Values, Reads Ignore Values (WPRI)}
 
 Some whole read/write fields are reserved for future use.  Software
 should ignore the values read from these fields, and should preserve
 the values held in these fields when writing values to other fields of
-the same register.  These fields are labeled \wpri\ in the register
-descriptions.
+the same register.
+For forward compatibility, implementations that do not furnish these fields
+must hardwire them to zero.
+These fields are labeled \wpri\ in the register descriptions.
 
 \begin{commentary}
 To simplify the software model, any backward-compatible future