From 4c178ac04d9c20eae896c6249ee99e08844c50a4 Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sat, 4 May 2019 00:34:35 +0100
Subject: [PATCH] add dependence cell scoreboard from 11.4.7

---
 src/scoreboard/dependence_cell.py | 99 +++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 src/scoreboard/dependence_cell.py

diff --git a/src/scoreboard/dependence_cell.py b/src/scoreboard/dependence_cell.py
new file mode 100644
index 00000000..103cf2d2
--- /dev/null
+++ b/src/scoreboard/dependence_cell.py
@@ -0,0 +1,99 @@
+from nmigen.compat.sim import run_simulation
+from nmigen.cli import verilog, rtlil
+from nmigen import Module, Signal, Elaboratable
+from nmutil.latch import SRLatch
+
+class DepencenceCell(Elaboratable):
+    """ implements 11.4.7 mitch alsup dependence cell, p27
+    """
+    def __init__(self):
+        # inputs
+        self.dest_i = Signal(reset_less=True)     # Dest in (top)
+        self.src1_i = Signal(reset_less=True)     # oper1 in (top)
+        self.src2_i = Signal(reset_less=True)     # oper2 in (top)
+        self.issue_i = Signal(reset_less=True)    # Issue in (top)
+
+        self.go_write_i = Signal(reset_less=True) # Go Write in (left)
+        self.go_read_i = Signal(reset_less=True)  # Go Read in (left)
+
+        # for Register File Select Lines (vertical)
+        self.dest_rsel_o = Signal(reset_less=True)  # dest reg sel (bottom)
+        self.src1_rsel_o = Signal(reset_less=True)  # src1 reg sel (bottom)
+        self.src2_rsel_o = Signal(reset_less=True)  # src2 reg sel (bottom)
+
+        # for Function Unit "forward progress" (horizontal)
+        self.dest_fwd_o = Signal(reset_less=True)   # dest FU fw (right)
+        self.src1_fwd_o = Signal(reset_less=True)   # src1 FU fw (right)
+        self.src2_fwd_o = Signal(reset_less=True)   # src2 FU fw (right)
+
+    def elaborate(self, platform):
+        m = Module()
+        m.submodules.dest_l = dest_l = SRLatch()
+        m.submodules.src1_l = src1_l = SRLatch()
+        m.submodules.src2_l = src2_l = SRLatch()
+
+        # destination latch: reset on go_write HI, set on dest and issue
+        m.d.sync += dest_l.s.eq(self.issue_i & self.dest_i)
+        m.d.sync += dest_l.r.eq(self.go_write_i)
+
+        # src1 latch: reset on go_read HI, set on src1_i and issue
+        m.d.sync += src1_l.s.eq(self.issue_i & self.src1_i)
+        m.d.sync += src1_l.r.eq(self.go_read_i)
+
+        # src2 latch: reset on go_read HI, set on op2_i and issue
+        m.d.sync += src2_l.s.eq(self.issue_i & self.src2_i)
+        m.d.sync += src2_l.r.eq(self.go_read_i)
+
+        # FU "Forward Progress" (read out horizontally)
+        m.d.comb += self.dest_rsel_o.eq(dest_l.q & self.go_write_i)
+        m.d.comb += self.src1_rsel_o.eq(src1_l.q & self.go_read_i)
+        m.d.comb += self.src2_rsel_o.eq(src2_l.q & self.go_read_i)
+
+        # Register File Select (read out vertically)
+        m.d.comb += self.dest_fwd_o.eq(dest_l.q & self.dest_i)
+        m.d.comb += self.src1_fwd_o.eq(src1_l.q & self.src1_i)
+        m.d.comb += self.src2_fwd_o.eq(src2_l.q & self.src2_i)
+
+        return m
+
+    def __iter__(self):
+        yield self.dest_i
+        yield self.src1_i
+        yield self.src2_i
+        yield self.issue_i
+        yield self.go_write_i
+        yield self.go_read_i
+        yield self.dest_rsel_o
+        yield self.src1_rsel_o
+        yield self.src2_rsel_o
+        yield self.dest_fwd_o
+        yield self.src1_fwd_o
+        yield self.src2_fwd_o
+                
+    def ports(self):
+        return list(self)
+
+def dcell_sim(dut):
+    yield dut.s.eq(0)
+    yield dut.r.eq(0)
+    yield
+    yield dut.s.eq(1)
+    yield
+    yield dut.s.eq(0)
+    yield
+    yield dut.r.eq(1)
+    yield
+    yield dut.r.eq(0)
+    yield
+    yield
+
+def test_dcell():
+    dut = DepencenceCell()
+    vl = rtlil.convert(dut, ports=dut.ports())
+    with open("test_dcell.il", "w") as f:
+        f.write(vl)
+
+    run_simulation(dut, dcell_sim(dut), vcd_name='test_dcell.vcd')
+
+if __name__ == '__main__':
+    test_dcell()
-- 
2.30.2