Add abstract "cond_t" type to detect state transitions.

We often need to watch for transitions between one state and another, so
that we can issue warnings or take action ONCE. This abstracts that "have I
already reacted to this" stuff into a single set of functions.

For example, this code reads a GPIO every time through the loop, but it only
generates an event when the GPIO value changes from 0 to 1:

    cond_t c;

    cond_init_false(&c);

    while(1) {
        int val = read_some_gpio();
        cond_set(&c, val);

        if (cond_went_true(&c))
            host_event(SOMETHING_HAPPENED);

        sleep(1);
    }

BUG=none
BRANCH=falco,peppy
TEST=manual

make BOARD=falco runtests

Change-Id: I42393fcf3c4eb71b9551118a0f442d55c0691315
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/65071

1 files changed, 57 insertions, 1 deletions

diff --git a/common/util.c b/common/util.c
index 5ccebeb063..0d7bff2710 100644
--- a/common/util.c
+++ b/common/util.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -272,3 +272,59 @@ int uint64divmod(uint64_t *n, int d)
 	*n = q;
 	return r;
 }
+
+
+/****************************************************************************/
+/* stateful conditional stuff */
+
+enum cond_internal_bits {
+	COND_CURR_MASK = (1 << 0),		/* current value */
+	COND_RISE_MASK = (1 << 1),		/* set if 0->1 */
+	COND_FALL_MASK = (1 << 2),		/* set if 1->0 */
+};
+
+void cond_init(cond_t *c, int val)
+{
+	if (val)
+		*c = COND_CURR_MASK;
+	else
+		*c = 0;
+}
+
+int cond_is(cond_t *c, int val)
+{
+	if (val)
+		return *c & COND_CURR_MASK;
+	else
+		return !(*c & COND_CURR_MASK);
+}
+
+
+void cond_set(cond_t *c, int val)
+{
+	if (val && cond_is(c, 0))
+		*c |= COND_RISE_MASK;
+	else if (!val && cond_is(c, 1))
+		*c |= COND_FALL_MASK;
+	if (val)
+		*c |= COND_CURR_MASK;
+	else
+		*c &= ~COND_CURR_MASK;
+}
+
+
+int cond_went(cond_t *c, int val)
+{
+	int ret;
+
+	if (val) {
+		ret = *c & COND_RISE_MASK;
+		*c &= ~COND_RISE_MASK;
+	}
+	else {
+		ret = *c & COND_FALL_MASK;
+		*c &= ~COND_FALL_MASK;
+	}
+
+	return ret;
+}