diff --git a/smpc.h b/smpc.h
index 246b6ec..694f8d2 100644
--- a/smpc.h
+++ b/smpc.h
@@ -235,6 +235,22 @@ enum comreg_bit {
   COMREG__RESDISA = 0x1A,
 };
 
+enum oreg_bit {
+  OREG31__MSHON    = 0b0000'0000,
+  OREG31__SSHON    = 0b0000'0010,
+  OREG31__SSHOFF   = 0b0000'0011,
+  OREG31__SNDON    = 0b0000'0110,
+  OREG31__SNDOFF   = 0b0000'0111,
+  OREG31__CDON     = 0b0000'1000,
+  OREG31__CDOFF    = 0b0000'1001,
+  OREG31__SYSRES   = 0b0000'1101,
+  OREG31__CKCHG352 = 0b0000'1110,
+  OREG31__CKCHG320 = 0b0000'1111,
+  OREG31__NMIREQ   = 0b0001'1000,
+  OREG31__RESENAB  = 0b0001'1001,
+  OREG31__RESDISA  = 0b0001'1010,
+};
+
 enum intback_ireg_bit {
   INTBACK__IREG0__CONTINUE = (1 << 7),
   INTBACK__IREG0__BREAK = (1 << 6),