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back.pysim: raise an exception if delta cycles blow a process deadline.

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whitequark 2018-12-14 08:10:21 +00:00
parent a10791e160
commit 6aefd0c04c
1 changed files with 15 additions and 1 deletions
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16
nmigen/back/pysim.py
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@ -7,7 +7,11 @@ from ..fhdl.ast import *
from ..fhdl.xfrm import ValueTransformer, StatementTransformer from ..fhdl.xfrm import ValueTransformer, StatementTransformer
__all__ = ["Simulator", "Delay", "Passive"] __all__ = ["Simulator", "Delay", "Tick", "Passive", "DeadlineError"]
class DeadlineError(Exception):
pass
class _State: class _State:
@ -426,9 +430,19 @@ class Simulator:
.format(stmt, proc)) .format(stmt, proc))
def step(self, run_passive=False): def step(self, run_passive=False):
deadline = None
if self._wait_deadline:
# We might run some delta cycles, and we have simulator processes waiting on
# a deadline. Take care to not exceed the closest deadline.
deadline = min(self._wait_deadline.values())
# Are there any delta cycles we should run? # Are there any delta cycles we should run?
while self._state.curr_dirty: while self._state.curr_dirty:
self._timestamp += self._epsilon self._timestamp += self._epsilon
if deadline is not None and self._timestamp >= deadline:
# 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?")
domains = set() domains = set()
self._update_dirty_signals() self._update_dirty_signals()