diff --git a/chapter7.adoc b/chapter7.adoc
index 952e49a..179599f 100644
--- a/chapter7.adoc
+++ b/chapter7.adoc
@@ -160,6 +160,9 @@ domains. To emulate an IMSIC, the RDSM may use the illegal instruction trap on
 access to the associated CSRs for emulation purposes.
 ====
 
+If `Smsdia` extension is implemented, then `msdcfg.SDICN` is non-zero at reset
+and holds the number of an implemented supervisor domain interrupt controller.
+
 === Machine supervisor domain external interrupt pending (`msdeip/msdeiph`)
 
 The `msdeip` is a MXLEN-bit read-only register, formatted for MXLEN=64 as