From 6fec08e28f4886e71775a1e8bd6202233ef3ff5e Mon Sep 17 00:00:00 2001
From: Yehowshua <Yehowshua@web>
Date: Tue, 5 May 2020 16:44:22 +0100
Subject: [PATCH]

---
 Documentation/SOC/index.mdwn | 65 ++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/Documentation/SOC/index.mdwn b/Documentation/SOC/index.mdwn
index 3c56d8adb..7c8447d8b 100644
--- a/Documentation/SOC/index.mdwn
+++ b/Documentation/SOC/index.mdwn
@@ -1 +1,66 @@
 The SOC is designed to be compliant with POWER 3.0B with somewhere near 300 instructions excluding Vector instructions.
+
+# Decoder
+
+The Decoder currently uses a class called PowerOp which get instantiated for every instruction. PowerOp class instantiation has member objects who's values get set respectively for each instruction.
+
+We use Pythons Enums to help with common decoder values.
+Below is the POWER add insruction.
+
+| opcode       | unit | internal op | in1 | in2 | in3  | out | CR in | CR out | inv A | inv out | cry in | cry out | ldst len | BR | sgn ext | upd | rsrv | 32b | sgn | rc | lk | sgl pipe | comment | form |
+|--------------|------|-------------|-----|-----|------|-----|-------|--------|-------|---------|--------|---------|----------|----|---------|-----|------|-----|-----|----|----|----------|---------|------|
+| 0b0100001010 | ALU  | OP_ADD      | RA  | RB  | NONE | RT  | 0     | 0      | 0     | 0       | ZERO   | 0       | NONE     | 0  | 0       | 0   | 0    | 0   | 0   | RC | 0  | 0        | add     | XO   |
+
+Here is an example of a toy multiplexer that sets various fields in the PowerOP signal class when 1 is set.
+
+    from nmigen import Module, Elaboratable, Signal, Cat, Mux
+    from soc.decoder.power_enums import (Function, Form, InternalOp,
+                             In1Sel, In2Sel, In3Sel, OutSel, RC, LdstLen,
+                             CryIn, get_csv, single_bit_flags,
+                             get_signal_name, default_values)
+    from soc.decoder.power_fields import DecodeFields
+    from soc.decoder.power_fieldsn import SigDecode, SignalBitRange
+    from soc.decoder.power_decoder import PowerOp
+    
+    class Op_Add_Example(Elaboratable):
+        def __init__(self):
+            self.select = Signal()
+            self.op_add = PowerOp()
+        
+        def elaborate(self, platform):
+            m = Module()
+            op_add = self.op_add
+    
+            with m.If(self.select == 1):
+                m.d.comb += op_add.function_unit.eq(Function['ALU'])
+                m.d.comb += op_add.form.eq(Form['XO'])
+                m.d.comb += op_add.internal_op.eq(InternalOp['OP_ADD'])
+                m.d.comb += op_add.in1_sel.eq(In1Sel['RA'])
+                m.d.comb += op_add.in2_sel.eq(In2Sel['RB'])
+                m.d.comb += op_add.in3_sel.eq(In3Sel['NONE'])
+                m.d.comb += op_add.out_sel.eq(OutSel['RT'])
+                m.d.comb += op_add.rc_sel.eq(RC['RC'])
+                m.d.comb += op_add.ldst_len.eq(LdstLen['NONE'])
+                m.d.comb += op_add.cry_in.eq(CryIn['ZERO'])
+            
+            with m.Else():
+                m.d.comb += op_add.function_unit.eq(0)
+                m.d.comb += op_add.form.eq(0)
+                m.d.comb += op_add.internal_op.eq(0)
+                m.d.comb += op_add.in1_sel.eq(0)
+                m.d.comb += op_add.in2_sel.eq(0)
+                m.d.comb += op_add.in3_sel.eq(0)
+                m.d.comb += op_add.out_sel.eq(0)
+                m.d.comb += op_add.rc_sel.eq(0)
+                m.d.comb += op_add.ldst_len.eq(0)
+                m.d.comb += op_add.cry_in.eq(0)
+            
+            return m
+    
+    from nmigen.back import verilog
+    verilog_file = "op_add_example.v"
+    top = Op_Add_Example()
+    f = open(verilog_file, "w")
+    verilog =  verilog.convert(top, name='top', strip_internal_attrs=True, ports= top.op_add.ports())
+    f.write(verilog)
+    print(f"Verilog Written to: {verilog_file}")
-- 
2.30.2