comment on why clocks are in FSM

[c4m-jtag.git] / c4m / nmigen / jtag / tap.py

diff --git a/c4m/nmigen/jtag/tap.py b/c4m/nmigen/jtag/tap.py
index a6b702fd7786c751355eac1f2a0ab92a8307c53a..2753063b0c391249297785a21c9e065867a3bfd9 100755 (executable)
--- a/c4m/nmigen/jtag/tap.py
+++ b/c4m/nmigen/jtag/tap.py
@@ -26,6 +26,7 @@ class _FSM(Elaboratable):
         self.shift = Signal()
         self.update = Signal()
 
+        # JTAG uses both edges of the incoming clock (TCK). set them up here
         self.posjtag = ClockDomain("posjtag", local=True)
         self.negjtag = ClockDomain("negjtag", local=True, clk_edge="neg")