Such wires are likely to trigger pathological behavior in Yosys and,
if applicable, other toolchains that consume Verilog converted from
RTLIL.
Fixes#341.
Before this commit, selecting a part that was fully out of bounds of
a value was correctly implemented as a write to a dummy wire, but
selecting a part that was only partially out of bounds resulted in
a crash.
Fixes#351.
This has been originally implemented in commit d3775eed (which fixed
`write_vcd(traces=)` to do something at all), but had a flaw where
undriven traces would not be correctly placed in hierarchy. This
used to produce incorrect results on pyvcd 0.1, but started causing
assertion failures on pyvcd 0.2.
Fixes#345.
Because write_vcd() is a context manager, this is useful if the VCD
file should be sometimes not written, since it avoids awkward
conditionals with duplicated code. It's not very elegant though.
Fixes#319.
Before this commit, there was no way to do so besides creating and
assigning an intermediate signal, which could not be extracted into
a helper function due to Module statefulness.
Fixes#292.
Before this commit, only signals driven from fragments (in practice,
everything except toplevel inputs) would get written to a VCD file.
Not having toplevel inputs in the dump made debugging ~impossible.
After this commit, all signals the fragment refers to get written to
a VCD file. (More specifically, all signals the compiler assigns
an index to, i.e. signals the generated code reads or writes.)
Fixes#280.
These are not desirable in a HDL, and currently elaborate to broken
RTLIL (after YosysHQ/yosys#1551); prohibit them completely, like
we already do for division and modulo.
Fixes#302.
The redesign introduces no fundamental incompatibilities, but it does
involve minor breaking changes:
* The simulator commands were moved from hdl.ast to back.pysim
(instead of only being reexported from back.pysim).
* back.pysim.DeadlineError was removed.
Summary of changes:
* The new simulator compiles HDL to Python code and is >6x faster.
(The old one compiled HDL to lots of Python lambdas.)
* The new simulator is a straightforward, rigorous implementation
of the Synchronous Reactive Programming paradigm, instead of
a pile of ad-hoc code with no particular design driving it.
* The new simulator never raises DeadlineError, and there is no
limit on the amount of delta cycles.
* The new simulator robustly handles multiclock designs.
* The new simulator can be reset, such that the compiled design
can be reused, which can save significant runtime with large
designs.
* Generators can no longer be added as processes, since that would
break reset(); only generator functions may be. If necessary,
they may be added by wrapping them into a generator function;
a deprecated fallback does just that. This workaround will raise
an exception if the simulator is reset and restarted.
* The new simulator does not depend on Python extensions.
(The old one required bitarray, which did not provide wheels.)
Fixes#28.
Fixes#34.
Fixes#160.
Fixes#161.
Fixes#215.
Fixes#242.
Fixes#262.
$verilog_initial_trigger was introduced to work around Verilog
simulation semantics issues with `always @*` statements that only
have constants on RHS and in conditions. Unfortunately, it breaks
Verilator. Since the combination of proc_prune and proc_clean passes
eliminates all such statements, it can be simply removed when both
of these passes are available, currently on Yosys master. After
Yosys 0.10 is released, we can get rid of $verilog_initial_trigger
entirely.
This can cause confusion:
* If the erroneous object is None, it is printed as 'None', which
appears as a string (and could be the result of converting None
to a string.)
* If the erroneous object is a string, it is printed as ''<val>'',
which is a rather strange combination of quotes.
Although useful for debugging, most external tools often complain
about such attributes (with notable exception of Vivado). As such,
it is better to emit Verilog with these attributes into a separate
file such as `design.debug.v` and only emit the attributes that were
explicitly placed by the user to `design.v`.
This still leaves the (*init*) attribute. See #220 for details.
Also, replace `bits, sign = x.shape()` with more idiomatic
`width, signed = x.shape()`.
This unifies all properties corresponding to `len(x)` to `x.width`.
(Not all values have a `width` property.)
Fixes#210.
