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, 47 insertions, 0 deletions

diff --git a/include/util.h b/include/util.h
index ed30ed4e46..0408940b35 100644
--- a/include/util.h
+++ b/include/util.h
@@ -101,4 +101,51 @@ int tolower(int c);
  */
 int uint64divmod(uint64_t *v, int by);
 
+
+/****************************************************************************/
+/* Conditional stuff.
+ *
+ * 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:
+ *
+ *     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);
+ *     }
+ *
+ */
+typedef uint8_t cond_t;
+
+/* Initialize a conditional to a specific state. Do this first. */
+void cond_init(cond_t *c, int boolean);
+static inline void cond_init_false(cond_t *c) { cond_init(c, 0); }
+static inline void cond_init_true(cond_t *c) { cond_init(c, 1); }
+
+/* Set the current state. Do this as often as you like. */
+void cond_set(cond_t *c, int boolean);
+static inline void cond_set_false(cond_t *c) { cond_set(c, 0); }
+static inline void cond_set_true(cond_t *c) { cond_set(c, 1); }
+
+/* Get the current state. Do this as often as you like. */
+int cond_is(cond_t *c, int boolean);
+static inline int cond_is_false(cond_t *c) { return cond_is(c, 0); }
+static inline int cond_is_true(cond_t *c) { return cond_is(c, 1); }
+
+/* See if the state has transitioned. If it has, the corresponding function
+ * will return true ONCE only, until it's changed back.
+ */
+int cond_went(cond_t *c, int boolean);
+static inline int cond_went_false(cond_t *c) { return cond_went(c, 0); }
+static inline int cond_went_true(cond_t *c) { return cond_went(c, 1); }
+
 #endif  /* __CROS_EC_UTIL_H */