tb: fix timer reset; cosmetic fixes.

power_fv/tb.py

@@ -5,47 +5,46 @@ from amaranth.asserts import *
 __all__ = ["Testbench"]
 
 
+def _check_triggers(t_start, t_pre, t_post):
+    if not isinstance(t_start, int) or t_start <= 0:
+        raise ValueError("t_start must be a positive integer, not {!r}"
+                         .format(t_start))
+    if not isinstance(t_post, int) or t_post < t_start:
+        raise ValueError("t_post must be an integer greater than or equal to t_start ({}), not {!r}"
+                         .format(t_start, t_post))
+    if not isinstance(t_pre, int) or t_pre > t_post or t_pre < t_start:
+        raise ValueError("t_pre must be an integer between t_start and t_post (i.e. [{},{}]), "
+                         "not {!r}".format(t_pre, t_start, t_post))
+
+
 class Testbench(Elaboratable):
-    def __init__(self, check, dut, *, t_post, t_pre=None, t_start=0):
-        if not isinstance(t_post, int) or t_post < 0:
-            raise ValueError("t_post must be a non-negative integer, not {!r}"
-                             .format(t_post))
-        if t_pre is None:
+    def __init__(self, check, dut, *, t_start=1, t_pre=None, t_post=20):
+        if t_pre is None and t_post is not None:
             t_pre = t_post
-        if not isinstance(t_pre, int) or t_pre < 0:
-            raise ValueError("t_pre must be a non-negative integer, not {!r}"
-                             .format(t_pre))
-        if t_pre > t_post:
-            raise ValueError("t_pre ({}) must be lesser than or equal to t_post ({})"
-                             .format(t_pre, t_post))
-        if not isinstance(t_start, int) or t_start < 0:
-            raise ValueError("t_start must be a non-negative integer, not {!r}"
-                             .format(t_start))
-        if t_start > t_pre:
-            raise ValueError("t_start ({}) must be lesser than or equal to t_pre ({})"
-                             .format(t_start, t_pre))
 
-        self.t_post  = t_post
-        self.t_pre   = t_pre
-        self.t_start = t_start
+        _check_triggers(t_start, t_pre, t_post)
 
         self.check   = check
         self.dut     = dut
+        self.t_start = t_start
+        self.t_pre   = t_pre
+        self.t_post  = t_post
 
     def elaborate(self, platform):
         m = Module()
 
-        timer = Signal(range(self.t_post + 1))
-        with m.If(timer != self.t_post):
+        timer = Signal(range(self.t_post + 2), reset=1)
+
+        with m.If(timer <= self.t_post):
             m.d.sync += timer.eq(timer + 1)
 
         m.submodules.check = ResetInserter(timer < self.t_start)(self.check)
         m.submodules.dut   = self.dut
 
         m.d.comb += [
-            self.check.dut .eq(self.dut.pfv),
             self.check.pre .eq(timer == self.t_pre),
             self.check.post.eq(timer == self.t_post),
+            self.check.pfv .eq(self.dut.pfv),
         ]
 
         m.d.comb += Assume(ResetSignal() == Initial())