Adding the Permission Validator. Needs Tests!

diff --git a/TLB/PermissionValidator.py b/TLB/PermissionValidator.py
new file mode 100644 (file)
index 0000000..86050d2
--- /dev/null
+++ b/TLB/PermissionValidator.py
@@ -0,0 +1,53 @@
+from nmigen import *
+from nmigen.cli import main
+
+# The purpose of this Module is to check the Permissions of a given PTE 
+# against the requested access permissions. 
+# This module will either validate (by setting the valid bit HIGH) the request
+# or find a permission fault and invalidate (by setting the valid bit LOW) 
+# the request
+class PermissionValidator():
+    def __init__(self, data_size):
+        # Input
+        self.data = Signal(data_size);
+        self.xwr = Signal(3) # Execute, Write, Read
+        self.super = Signal(1) # Supervisor Mode
+        self.super_access = Signal(1) # Supervisor Access
+        self.asid = Signal(15) # Address Space IDentifier (ASID)
+        
+        # Output
+        self.valid = Signal(1) # Denotes if the permissions are correct
+        
+    def elaborate(self, platform):
+        m = Module()
+        m.d.comb += [
+            # Check if ASID matches OR entry is global
+            If(data[98:113] == self.asid or data[5] == 1,
+               # Check Execute, Write, Read (XWR) Permissions
+               If(data[3] == self.xwr[2] and data[2] == self.xwr[1] and data[1] == self.xwr[0],
+                  # Check if supervisor
+                  If(self.super == 1,
+                     # Check if entry is in user mode
+                     # Check if supervisor has access
+                     If(data[4] == 0,
+                        self.valid.eq(1)
+                     ).Elif(self.super_access == 1,
+                        self.valid.eq(1)
+                     ).Else(
+                        self.valid.eq(0)
+                     )
+                  ).Else(
+                      # Check if entry is in user mode
+                      If(data[4] == 1,
+                         self.valid.eq(1)
+                      ).Else(
+                         self.valid.eq(0) 
+                      )
+                  )
+               ).Else(
+                   self.valid.eq(0)                   
+               )
+            ).Else(
+                self.valid.eq(0)
+            )
+        ]
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