From ab97e79926e865df8fd7b86cdf96d756012542fe Mon Sep 17 00:00:00 2001
From: tmeissner <programming@goodcleanfun.de>
Date: Tue, 16 Jun 2020 16:13:53 +0200
Subject: [PATCH] Add example for log iff (<->) operator, was fixed in
 ghdl/ghdl#1371

---
 README.md                       |  1 +
 formal/psl_logical_iff.sby      | 18 +++++++++++
 formal/tests.mk                 |  3 +-
 src/psl_logical_iff.vhd         | 54 +++++++++++++++++++++++++++++++++
 src/psl_logical_implication.vhd |  1 -
 5 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 formal/psl_logical_iff.sby
 create mode 100644 src/psl_logical_iff.vhd

diff --git a/README.md b/README.md
index 379de7e..853eb68 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,7 @@ The next lists will grow during further development
 * `always` operator
 * `never` operator
 * logical implication operator (`->`)
+* logical iff operator (`<->`)
 * `next` operator
 * `next[n]` operator
 * `next_a[i to j]` operator
diff --git a/formal/psl_logical_iff.sby b/formal/psl_logical_iff.sby
new file mode 100644
index 0000000..78e91f5
--- /dev/null
+++ b/formal/psl_logical_iff.sby
@@ -0,0 +1,18 @@
+[tasks]
+bmc
+
+[options]
+depth 25
+bmc: mode bmc
+
+[engines]
+bmc: smtbmc z3
+
+[script]
+bmc: ghdl --std=08 pkg.vhd sequencer.vhd psl_logical_iff.vhd -e psl_logical_iff
+prep -top psl_logical_iff
+
+[files]
+../src/pkg.vhd
+../src/sequencer.vhd
+../src/psl_logical_iff.vhd
diff --git a/formal/tests.mk b/formal/tests.mk
index 6d1217c..98e27cf 100644
--- a/formal/tests.mk
+++ b/formal/tests.mk
@@ -29,4 +29,5 @@ psl_sere_fusion \
 psl_prev \
 psl_stable \
 psl_rose \
-psl_fell
+psl_fell \
+psl_logical_iff
diff --git a/src/psl_logical_iff.vhd b/src/psl_logical_iff.vhd
new file mode 100644
index 0000000..ea6c4dc
--- /dev/null
+++ b/src/psl_logical_iff.vhd
@@ -0,0 +1,54 @@
+library ieee;
+  use ieee.std_logic_1164.all;
+
+use work.pkg.all;
+
+
+entity psl_logical_iff is
+  port (
+    clk : in std_logic
+  );
+end entity psl_logical_iff;
+
+
+architecture psl of psl_logical_iff is
+
+  signal a, b, c : std_logic;
+
+begin
+
+
+  --                              01234567890
+  SEQ_A : sequencer generic map ("_-__-___-__") port map (clk, a);
+  SEQ_B : sequencer generic map ("_-______-__") port map (clk, b);
+  SEQ_C : sequencer generic map ("_-__-______") port map (clk, c);
+
+
+  -- All is sensitive to rising edge of clk
+  default clock is rising_edge(clk);
+
+  -- This assertion holds
+  IFF_0_a : assert always (a <-> b or c);
+
+  -- Equivalent but with logical implication operator
+  -- This assertion holds
+  IFF_1_a : assert always (a -> b or c) and (b or c -> a);
+
+  -- This assertion doesn't hold at cycle 4
+  IFF_2_a : assert always (a <-> b and c);
+
+  -- This assertion doesn't hold at cycle 0
+  IFF_3_a : assert always (a <-> true);
+
+  -- This assertion doesn't hold at cycle 1
+  IFF_4_a : assert always (a -> false);
+
+
+  -- Stop simulation after longest running sequencer is finished
+  -- Simulation only code by using pragmas
+  -- synthesis translate_off
+  stop_sim(clk, 11);
+  -- synthesis translate_on
+
+
+end architecture psl;
diff --git a/src/psl_logical_implication.vhd b/src/psl_logical_implication.vhd
index 690ced2..64d884b 100644
--- a/src/psl_logical_implication.vhd
+++ b/src/psl_logical_implication.vhd
@@ -25,7 +25,6 @@ begin
   SEQ_D : sequencer generic map ("___________") port map (clk, d);
 
 
-
   -- All is sensitive to rising edge of clk
   default clock is rising_edge(clk);