Remove option to hardwire UXL/SXL to 0

1 files changed, 7 insertions, 4 deletions

diff --git a/src/supervisor.tex b/src/supervisor.tex
index 2db7c61..9aa0cdb 100644
--- a/src/supervisor.tex
+++ b/src/supervisor.tex
@@ -191,10 +191,13 @@ sstatus} is equivalent to reading or writing the homonymous field in
 The UXL field controls the value of XLEN for U-mode, termed {\em U-XLEN},
 which may differ from the value of XLEN for S-mode, termed {\em S-XLEN}.  The
 encoding of UXL is the same as that of the MXL field of {\tt misa}, shown in
-Table~\ref{misabase}.  This field only exists for RV64 and RV128; RV32
-machines always use RV32 for U-mode.  UXL is a \warl\ field, and an
-implementation may hard-wire UXL to zero, in which case U-XLEN~=~S-XLEN.  If
-U-XLEN~$\ne$~S-XLEN, instructions executed in the narrower mode must ignore
+Table~\ref{misabase}.
+
+For RV32 systems, the UXL field does not exist, and U-XLEN~=~32.  For RV64 and
+RV128 systems, it is a \warl\ field that encodes the current value of U-XLEN.
+In particular, the implementation may hardwire UXL so that U-XLEN~=~S-XLEN.
+
+If U-XLEN~$\ne$~S-XLEN, instructions executed in the narrower mode must ignore
 source register operand bits above the configured XLEN, and must sign-extend
 results to fill the widest supported XLEN in the destination register.