Fix an off-by-one error in defining coarse-grained PMPs for NAPOT

1 files changed, 7 insertions, 6 deletions

diff --git a/src/machine.tex b/src/machine.tex
index ca9abbc..7bebe67 100644
--- a/src/machine.tex
+++ b/src/machine.tex
@@ -2897,12 +2897,13 @@ PMP entry 0's A field is set to TOR, zero is used for the lower bound, and so
 it matches any address $y < {\tt pmpaddr}_0$.
 
 Although the PMP mechanism supports regions as small as four bytes, platforms
-may specify coarser PMP regions. In general, the PMP grain is
-$2^{G+2}$ bytes and must be the same across all PMP regions.  When $G>0$, the
-NA4 mode may not be selected.  Furthermore, bits ${\tt pmpaddr}_i$[G-1:0] all
-read as equal to ${\tt pmpcfg}_i$.A[1], i.e., all ones when the mode is NAPOT,
-or all zeros when the mode is TOR or OFF.  Bits ${\tt pmpaddr}_i$[G-1:0] do
-not affect the address-matching logic.
+may specify coarser PMP regions. In general, the PMP grain is $2^{G+2}$ bytes
+and must be the same across all PMP regions.  When $G \geq 1$, the NA4 mode
+may not be selected.  When $G \geq 2$ and ${\tt pmpcfg}_i$.A[1] is set, i.e.
+the mode is NAPOT, then bits ${\tt pmpaddr}_i$[G-2:0] read as all ones.  When
+$G \geq 1$ and ${\tt pmpcfg}_i$.A[1] is clear, i.e. the mode is OFF or TOR,
+then bits ${\tt pmpaddr}_i$[G-1:0] read as all zeros.  Bits ${\tt
+pmpaddr}_i$[G-1:0] do not affect the TOR address-matching logic.
 
 \begin{commentary}
 Software may determine the PMP granularity by writing zero to {\tt pmp0cfg},