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back.pysim: count delta cycles separately to avoid clock drift.

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This commit is contained in:
whitequark 2018-12-14 20:52:41 +00:00
parent a6a8703a0e
commit 0015713bfb
1 changed files with 9 additions and 4 deletions
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13
nmigen/back/pysim.py
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@ -204,6 +204,7 @@ class Simulator:
self._started = False
self._timestamp = 0.
self._delta = 0.
self._epsilon = 1e-10
self._fastest_clock = self._epsilon
self._state = _State()
@ -401,7 +402,8 @@ class Simulator:
var_value = signal.decoder(new).replace(" ", "_")
else:
var_value = new
self._vcd_writer.change(vcd_signal, self._timestamp / self._epsilon, var_value)
vcd_timestamp = (self._timestamp + self._delta) / self._epsilon
self._vcd_writer.change(vcd_signal, vcd_timestamp, var_value)
def _commit_comb_signals(self, domains):
"""Perform the comb part of IR processes (aka RTLIL always)."""
@ -417,7 +419,7 @@ class Simulator:
while domains:
# Advance the timeline a bit (purely for observational purposes) and commit all of them
# at the same timestamp.
self._timestamp += self._epsilon
self._delta += self._epsilon
curr_domains, domains = domains, set()
while curr_domains:
@ -509,7 +511,8 @@ class Simulator:
if self._state.curr_dirty:
# We might run some delta cycles, and we have simulator processes waiting on
# a deadline. Take care to not exceed the closest deadline.
if self._wait_deadline and self._timestamp >= min(self._wait_deadline.values()):
if self._wait_deadline and \
(self._timestamp + self._delta) >= min(self._wait_deadline.values()):
# Oops, we blew the deadline. We *could* run the processes now, but this is
# virtually certainly a logic loop and a design bug, so bail out instead.d
raise DeadlineError("Delta cycles exceeded process deadline; combinatorial loop?")
@ -537,6 +540,7 @@ class Simulator:
del self._wait_deadline[process]
self._suspended.remove(process)
self._timestamp = deadline
self._delta = 0.
self._run_process(process)
return True
@ -556,7 +560,8 @@ class Simulator:
def __exit__(self, *args):
if self._vcd_writer:
self._vcd_writer.close(self._timestamp / self._epsilon)
vcd_timestamp = (self._timestamp + self._delta) / self._epsilon
self._vcd_writer.close(vcd_timestamp)
if self._vcd_file and self._gtkw_file:
gtkw_save = GTKWSave(self._gtkw_file)