split out nmutil library based on ieee754fpu code

[nmutil.git] / src / nmutil / latch.py

diff --git a/src/nmutil/latch.py b/src/nmutil/latch.py
new file mode 100644 (file)
index 0000000..84235ff
--- /dev/null
+++ b/src/nmutil/latch.py
@@ -0,0 +1,100 @@
+from nmigen.compat.sim import run_simulation
+from nmigen.cli import verilog, rtlil
+from nmigen import Signal, Module, Const, Elaboratable
+
+""" jk latch
+
+module jk(q,q1,j,k,c);
+output q,q1;
+input j,k,c;
+reg q,q1;
+initial begin q=1'b0; q1=1'b1; end
+always @ (posedge c)
+  begin
+    case({j,k})
+         {1'b0,1'b0}:begin q=q; q1=q1; end
+         {1'b0,1'b1}: begin q=1'b0; q1=1'b1; end
+         {1'b1,1'b0}:begin q=1'b1; q1=1'b0; end
+         {1'b1,1'b1}: begin q=~q; q1=~q1; end
+    endcase
+   end
+endmodule
+"""
+
+def latchregister(m, incoming, outgoing, settrue):
+    reg = Signal.like(incoming) # make register same as input. reset is OK.
+    with m.If(settrue):
+        m.d.sync += reg.eq(incoming)      # latch input into register
+        m.d.comb += outgoing.eq(incoming) # return input (combinatorial)
+    with m.Else():
+        m.d.comb += outgoing.eq(reg) # return input (combinatorial)
+
+
+class SRLatch(Elaboratable):
+    def __init__(self, sync=True, llen=1):
+        self.sync = sync
+        self.llen = llen
+        self.s = Signal(llen, reset=0)
+        self.r = Signal(llen, reset=(1<<llen)-1) # defaults to off
+        self.q = Signal(llen, reset_less=True)
+        self.qn = Signal(llen, reset_less=True)
+        self.qlq = Signal(llen, reset_less=True)
+
+    def elaborate(self, platform):
+        m = Module()
+        q_int = Signal(self.llen)
+
+        m.d.sync += q_int.eq((q_int & ~self.r) | self.s)
+        if self.sync:
+            m.d.comb += self.q.eq(q_int)
+        else:
+            m.d.comb += self.q.eq((q_int & ~self.r) | self.s)
+        m.d.comb += self.qn.eq(~self.q)
+        m.d.comb += self.qlq.eq(self.q | q_int) # useful output
+
+        return m
+
+    def ports(self):
+        return self.s, self.r, self.q, self.qn
+
+
+def sr_sim(dut):
+    yield dut.s.eq(0)
+    yield dut.r.eq(0)
+    yield
+    yield
+    yield
+    yield dut.s.eq(1)
+    yield
+    yield
+    yield
+    yield dut.s.eq(0)
+    yield
+    yield
+    yield
+    yield dut.r.eq(1)
+    yield
+    yield
+    yield
+    yield dut.r.eq(0)
+    yield
+    yield
+    yield
+
+def test_sr():
+    dut = SRLatch(llen=4)
+    vl = rtlil.convert(dut, ports=dut.ports())
+    with open("test_srlatch.il", "w") as f:
+        f.write(vl)
+
+    run_simulation(dut, sr_sim(dut), vcd_name='test_srlatch.vcd')
+
+    dut = SRLatch(sync=False, llen=4)
+    vl = rtlil.convert(dut, ports=dut.ports())
+    with open("test_srlatch_async.il", "w") as f:
+        f.write(vl)
+
+    run_simulation(dut, sr_sim(dut), vcd_name='test_srlatch_async.vcd')
+
+if __name__ == '__main__':
+    test_sr()