This makes clk2fflogic add an attr to $ff cells that carry the state of
the emulated async FF. The $ff output doesn't have any async updates
that happened in the current cycle, but the $ff input does, so the $ff
input corresponds to the async FF's output in the original design.
Hence this patch also makes the following changes to passes besides
clk2fflogic (but only for FFs with the clk2fflogic attr set):
* opt_clean treats the input as a register name (instead of the
output)
* rename -witness ensures that the input has a public name
* the formal backends (smt2, btor, aiger) will use the input's
name for the initial state of the FF in witness files
* when sim reads a yw witness that assigns an initial value to the
input signal, the state update is redirected to the output
This ensures that yosys witness files for clk2fflogic designs have
useful and stable public signal names. It also makes it possible to
simulate a clk2fflogic witness on the original design (with some
limitations when the original design is already using $ff cells).
It might seem like setting the output of a clk2fflogic FF to update the
input's initial value might not work in general, but it works fine for
these reasons:
* Witnesses for FFs are only present in the initial cycle, so we do
not care about any later cycles.
* The logic that clk2fflogic generates loops the output of the
genreated FF back to the input, with muxes in between to apply any
edge or level sensitive updates. So when there are no active updates
in the current gclk cycle, there is a combinational path from the
output back to the input.
* The logic clk2fflogic generates makes sure that an edge sensitive
update cannot be active in the first cycle (i.e. the past initial
value is assumed to be whatever it needs to be to avoid an edge).
* When a level sensitive update is active in the first gclk cycle, it
is actively driving the output for the whole gclk cycle, so ignoring
any witness initialization is the correct behavior.
This was renaming cells while iterating over them which would always
cause an assertion failure. Apparently having to rename cells to make
all witness signals public is rarely required, so this slipped through.
In two places, we are joining label pieces by a '|' separator. We go
about it by putting the separator behind each entry, then removing the
trailing separator in a final fixup pass on the built string. For easier
reading, replace those occurrences by a new factored-out
'join_label_pieces' function.
Signed-off-by: Martin Povišer <povik@cutebit.org>
When the 'show' pass generates portboxes to detail the connection of
cell ports to wires, it has special handling of signal chunk
repetitions, but those repetitions are not accounted for in the
displayed bit range in case of cell outputs. Fix that, and so bring it
into consistence with the behavior on cell inputs.
So, taking for example the following Verilog snippet,
module DRIVER (Q);
output [7:0] Q;
assign Q = 8'b10101010;
endmodule
module main;
wire w;
DRIVER driver(.Q({8{w}}));
endmodule
make the show pass display '7:0 - 8x 0:0' in the driver-to-w portbox
instead of '7:7 - 8x 0:0' which it displayed formerly.
Signed-off-by: Martin Povišer <povik@cutebit.org>
This adds the xprop_decoder attribute to bwmuxes that drive the original
unencoded signals. Setundef is changed to ignore the x inputs of these
bwmuxes, so that they survive the prep script of SBY's formal flow. This
is required to make simulation (via sim) using the prep model show the
decoded x signals instead of 0/1 values made up by the solver.
Jannis Harder
N. Engelhardt
Miodrag Milanović
Aki Van Ness
gatecat
Claire Xenia Wolf
Martin Povišer
Peter Gadfort