From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 6 Jul 2020 18:49:49 +0000 (+0100)
Subject: investigating mul pipeline
X-Git-Tag: div_pipeline~162^2~29
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8ec43aad2185d0e14b4fc35fb43a828b93b53ce0;p=soc.git

investigating mul pipeline
---

diff --git a/src/soc/fu/mul/pipe_data.py b/src/soc/fu/mul/pipe_data.py
index 1d047bb8..1b37b484 100644
--- a/src/soc/fu/mul/pipe_data.py
+++ b/src/soc/fu/mul/pipe_data.py
@@ -19,7 +19,7 @@ class MulOutputData(IntegerData):
                ('XER', 'xer_so', '32'), # XER bit 32: SO
                ('XER', 'xer_ca', '34,45')] # XER bit 34/45: CA/CA32
     def __init__(self, pspec):
-        super().__init__(pspec, False)
+        super().__init__(pspec, False) # still input style
 
         self.neg_res = Signal(reset_less=True)
         self.neg_res32 = Signal(reset_less=True)
diff --git a/src/soc/fu/mul/post_stage.py b/src/soc/fu/mul/post_stage.py
index f2464085..e8e099bb 100644
--- a/src/soc/fu/mul/post_stage.py
+++ b/src/soc/fu/mul/post_stage.py
@@ -32,10 +32,8 @@ class MulMainStage3(PipeModBase):
         comb += is_32bit.eq(op.is_32bit)
 
         # check negate: select signed/unsigned
-        o_s = Signal(signed(o.data.width * 2), reset_less=True)
-        mul_o = Signal(o.data.width * 2, reset_less=True)
-        comb += o_s.eq(-o_i)
-        comb += mul_o.eq(Mux(self.i.neg_res, o_s, o_i))
+        mul_o = Signal(o_i.width, reset_less=True)
+        comb += mul_o.eq(Mux(self.i.neg_res, -o_i, o_i))
         comb += o.ok.eq(1)
 
         with m.Switch(op.insn_type):
@@ -67,8 +65,8 @@ class MulMainStage3(PipeModBase):
 
         # https://bugs.libre-soc.org/show_bug.cgi?id=319#c5
         ca = Signal(2, reset_less=True)
-        comb += ca[0].eq(mul_o[-1])                      # XER.CA
-        comb += ca[1].eq(mul_o[33] ^ (self.i.neg_res32)) # XER.CA32
+        comb += ca[0].eq(mul_o[-1])                      # XER.CA - XXX more?
+        comb += ca[1].eq(mul_o[32] ^ (self.i.neg_res32)) # XER.CA32
         comb += cry_o.data.eq(ca)
         comb += cry_o.ok.eq(1)
 
diff --git a/src/soc/fu/mul/pre_stage.py b/src/soc/fu/mul/pre_stage.py
index 3ce2f933..84363090 100644
--- a/src/soc/fu/mul/pre_stage.py
+++ b/src/soc/fu/mul/pre_stage.py
@@ -1,4 +1,5 @@
-# This stage is intended to do most of the work of executing multiply
+# This stage is intended to prepare the multiplication operands
+
 from nmigen import (Module, Signal, Mux)
 from nmutil.pipemodbase import PipeModBase
 from soc.fu.alu.pipe_data import ALUInputData
diff --git a/src/soc/fu/mul/test/test_pipe_caller.py b/src/soc/fu/mul/test/test_pipe_caller.py
index 5fa0779d..38e29a6a 100644
--- a/src/soc/fu/mul/test/test_pipe_caller.py
+++ b/src/soc/fu/mul/test/test_pipe_caller.py
@@ -77,7 +77,16 @@ class MulTestCase(FHDLTestCase):
         tc = TestCase(prog, self.test_name, initial_regs, initial_sprs)
         self.test_data.append(tc)
 
-    def test_rand_mullw(self):
+    def test_mullw(self):
+        lst = [f"mullw 3, 1, 2"]
+        initial_regs = [0] * 32
+        #initial_regs[1] = 0xffffffffffffffff
+        #initial_regs[2] = 0xffffffffffffffff
+        initial_regs[1] = 0x2ffffffff
+        initial_regs[2] = 0x2
+        self.run_tst_program(Program(lst), initial_regs)
+
+    def tst_rand_mullw(self):
         insns = ["mullw", "mullw.", "mullwo", "mullwo."]
         for i in range(40):
             choice = random.choice(insns)