Before this commit, each simulation engine (which is only pysim at
the moment, but also cxxsim soon) was a subclass of SimulatorCore,
and every simulation engine module would essentially duplicate
the complete structure of a simulator, with code partially shared.
This was a really bad idea: it was inconvenient to use, with
downstream code having to branch between e.g. PySettle and CxxSettle;
it had no well-defined external interface; it had multiple virtually
identical entry points; and it had no separation between simulation
algorithms and glue code.
This commit completely rearranges simulation code.
1. sim._base defines internal simulation interfaces. The clarity of
these internal interfaces is important because simulation
engines mix and match components to provide a consistent API
regardless of the chosen engine.
2. sim.core defines the external simulation interface: the commands
and the simulator facade. The facade provides a single entry
point and, when possible, validates or lowers user input.
It also imports built-in simulation engines by their symbolic
name, avoiding eager imports of pyvcd or ctypes.
3. sim.xxxsim (currently, only sim.pysim) defines the simulator
implementation: time and state management, process scheduling,
and waveform dumping.
The new simulator structure has none of the downsides of the old one.
See #324.
Before this commit, there was only occasional quoting of some names
used in any Tcl files. (I'm not sure what I was thinking.)
After this commit, any substs that may include Tcl special characters
are escaped. This does not include build names (which are explicitly
restricted to ASCII to avoid this problem), or attribute names (which
are chosen from a predefined set). Ideally we'd use a more principled
approach but Jinja2 does not support custom escaping mechanisms.
Note that Vivado restricts clock names to a more restrictive set that
forbids using Tcl special characters even when escaped.
Fixes#375.
For most toolchains, these are functionally identical, although ports
tend to work a bit better, being the common case. For Vivado, though,
it is necessary to place them on the port because its timing analyzer
considers input buffer delay.
Fixes#301.
Now environment variable overrides no longer infect the build scripts.
_toolchain.overrides is dropped as probably misguided in the first place.
Fixes#251.
