From 7555d7411c88d332803bfe341f4fa9dd5b6df957 Mon Sep 17 00:00:00 2001
From: Rohit Grover <rohit.grover@arm.com>
Date: Fri, 15 Aug 2014 13:17:00 +0100
Subject: [PATCH] add a cachedInterruptTimestamp to us_ticker_set_interrupt()
 to short-circuit duplicate calls.

---
 .../hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c     | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c b/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c
index f7b1b28b9b..ed763eb652 100644
--- a/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c
+++ b/libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c
@@ -58,6 +58,8 @@ static void us_ticker_app_timer_callback(void *context)
 
 void us_ticker_set_interrupt(unsigned int timestamp)
 {
+    static unsigned cachedInterruptTimestamp;
+
     if (!us_ticker_inited) {
         us_ticker_init();
     }
@@ -67,7 +69,13 @@ void us_ticker_set_interrupt(unsigned int timestamp)
             /* placeholder to do something to recover from error */
             return;
         }
+    } else {
+        /* we want to avoid taking action on duplicate requests */
+        if (timestamp == cachedInterruptTimestamp) {
+            return;
+        }
     }
+    cachedInterruptTimestamp = timestamp;
 
     uint32_t currentCounter;
     app_timer_cnt_get(&currentCounter);