add start on power decoder2

diff --git a/src/decoder/power_decoder2.py b/src/decoder/power_decoder2.py
new file mode 100644 (file)
index 0000000..0a19d30
--- /dev/null
+++ b/src/decoder/power_decoder2.py
@@ -0,0 +1,56 @@
+"""Power ISA Decoder second stage
+
+based on Anton Blanchard microwatt decode2.vhdl
+
+"""
+from nmigen import Module, Elaboratable, Signal
+from power_enums import InternalOp, CryIn
+
+
+class XerBits:
+    def __init__(self):
+        self.ca = Signal(reset_less=True)
+        self.ca32 = Signal(reset_less=True)
+        self.ov = Signal(reset_less=True)
+        self.ov32 = Signal(reset_less=True)
+        self.so = Signal(reset_less=True)
+
+
+class PowerDecodeToExecute(Elaboratable):
+
+    def __init__(self, width):
+
+        self.valid = Signal(reset_less=True)
+        self.insn_type = Signal(InternalOp, reset_less=True)
+        self.nia = Signal(64, reset_less=True)
+        self.write_reg = Signal(5, reset_less=True)
+        self.read_reg1 = Signal(5, reset_less=True)
+        self.read_reg2 = Signal(5, reset_less=True)
+        self.read_data1 = Signal(64, reset_less=True)
+        self.read_data2 = Signal(64, reset_less=True)
+        self.read_data3 = Signal(64, reset_less=True)
+        self.cr = Signal(32, reset_less=True)
+        self.xerc = XerBits()
+        self.lr = Signal(reset_less=True)
+        self.rc = Signal(reset_less=True)
+        self.oe = Signal(reset_less=True)
+        self.invert_a = Signal(reset_less=True)
+        self.invert_out = Signal(reset_less=True)
+        self.input_carry: Signal(CryIn, reset_less=True)
+        self.output_carry = Signal(reset_less=True)
+        self.input_cr = Signal(reset_less=True)
+        self.output_cr = Signal(reset_less=True)
+        self.is_32bit = Signal(reset_less=True)
+        self.is_signed = Signal(reset_less=True)
+        self.insn = Signal(32, reset_less=True)
+        self.data_len = Signal(4, reset_less=True) # bytes
+        self.byte_reverse  = Signal(reset_less=True)
+        self.sign_extend  = Signal(reset_less=True)# do we need this?
+        self.update  = Signal(reset_less=True) # is this an update instruction?
+
+    def elaborate(self, platform):
+        m = Module()
+        comb = m.d.comb
+
+        return m
+