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Add the $anyinit cell and the formalff pass

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These can be used to protect undefined flip-flop initialization values
from optimizations that are not sound for formal verification and can
help mapping all solver-provided values in witness traces for flows that
use different backends simultaneously.
This commit is contained in:
Jannis Harder 2022-07-21 14:22:15 +02:00
parent c26b2bf543
commit c0063288d6
16 changed files with 271 additions and 8 deletions
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8
kernel/ff.h
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@ -28,7 +28,10 @@ YOSYS_NAMESPACE_BEGIN
// Describes a flip-flop or a latch.
//
// If has_gclk, this is a formal verification FF with implicit global clock:
// Q is simply previous cycle's D.
// Q is simply previous cycle's D. Additionally if is_anyinit is true, this is
// an $anyinit cell which always has an undefined initialization value. Note
// that $anyinit is not considered to be among the FF celltypes, so a pass has
// to explicitly opt-in to process $anyinit cells with FfData.
//
// Otherwise, the FF/latch can have any number of features selected by has_*
// attributes that determine Q's value (in order of decreasing priority):
@ -126,6 +129,8 @@ struct FfData {
// True if this FF is a fine cell, false if it is a coarse cell.
// If true, width must be 1.
bool is_fine;
// True if this FF is an $anyinit cell. Depends on has_gclk.
bool is_anyinit;
// Polarities, corresponding to sig_*. True means active-high, false
// means active-low.
bool pol_clk;
@ -156,6 +161,7 @@ struct FfData {
has_sr = false;
ce_over_srst = false;
is_fine = false;
is_anyinit = false;
pol_clk = false;
pol_aload = false;
pol_ce = false;