renamed NoReg to Null in common

common/src/instructions.rs

@@ -69,7 +69,7 @@ pub enum Register {
     Idr,
     Mmr,
     Zero,
-    NoReg,
+    Null, // Invalid - Triggers a fault if accessed
 
     // system registers - can't be written to by instructions.
     Mar,
@@ -106,7 +106,7 @@ impl Register {
 
 impl Default for Register {
     fn default() -> Self {
-        Self::NoReg
+        Self::Null
     }
 }
 
@@ -144,7 +144,7 @@ impl TryFrom<u8> for Register {
             0x14 => Self::Idr,
             0x15 => Self::Mmr,
             0x16 => Self::Zero,
-            0x17 => Self::NoReg,
+            0x17 => Self::Null,
             0x18 => Self::Mar,
             0x19 => Self::Mdr,
             0x1A => Self::Sts,
@@ -183,7 +183,7 @@ impl TryFrom<&str> for Register {
             "idr" => Ok(Self::Idr),
             "mmr" => Ok(Self::Mmr),
             "zero" => Ok(Self::Zero),
-            "null" => Ok(Self::NoReg),
+            "null" => Ok(Self::Null),
             "pcx" => Ok(Self::Pcx),
             _ => Err(RegisterParseError::InvalidName(value.to_string())),
         }
@@ -216,7 +216,7 @@ impl std::fmt::Display for Register {
             Self::Idr => write!(f, "idr"),
             Self::Mmr => write!(f, "mmr"),
             Self::Zero => write!(f, "zero"),
-            Self::NoReg => write!(f, "noreg"),
+            Self::Null => write!(f, "null"),
             Self::Mar => write!(f, "mar"),
             Self::Mdr => write!(f, "mdr"),
             Self::Sts => write!(f, "sts"),