document decode functions

diff --git a/cpu_decoder.py b/cpu_decoder.py
index 995a04c1a4d9db41cb7d58912b142d38f9519d64..3cb0701ef06370d3e101f930da13b4329226e7ec 100644 (file)
--- a/cpu_decoder.py
+++ b/cpu_decoder.py
@@ -154,7 +154,7 @@ class CPUDecoder(Module):
         return self._decode_funct3(DA.jalr, [F3.jalr, ])
 
     def calculate_op_action(self):
-        """ decode op action
+        """ decode op action: the arith ops, and, or, add, xor, sr/sl etc.
         """
         c = {}
         immz = Constant(0, 12)
@@ -178,7 +178,7 @@ class CPUDecoder(Module):
         return Case(self.funct3, c)
 
     def calculate_misc_action(self):
-        """ decode misc mem action
+        """ decode misc mem action: fence and fence_i
         """
         c = {}
         immz = Constant(0, 12)
@@ -203,7 +203,7 @@ class CPUDecoder(Module):
         return Case(self.funct3, c)
 
     def calculate_system_action(self):
-        """ decode system action
+        """ decode opcode system: ebreak and csrs
         """
         c = {}
         b1 = Constant(1, 32)