From 571cf9364a4e640c956b5a110876c453dd698062 Mon Sep 17 00:00:00 2001
From: George Oikonomou <george@contiki-os.org>
Date: Mon, 9 Nov 2015 13:36:11 +0000
Subject: [PATCH] Improve CC13xx/CC26xx LPM logic

This commit applies a number of improvements to the logic used when trying to drop to a CC13xx/CC26xx low-power mode:

* We identify whether there are any pending etimers by using `etimer_pending()` instead of `etimer_next_expiration_time()`. This subsequently allows us to also identify whether an etimer is set to fire at time 0.
* We run a larger portion of the code with the global interrupt disabled. This prevents a number of messy conditions that can occur if an interrupt fires after we have started the low-power sequence.
* We check whether there are pending events earlier in the sequence.
* We make sure to schedule a next wakeup event even when an LPM module prohibits deep sleep and forces sleep instead.

This fixes some of the issues discussed in #1236
---
 cpu/cc26xx-cc13xx/lpm.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/cpu/cc26xx-cc13xx/lpm.c b/cpu/cc26xx-cc13xx/lpm.c
index c9e874824..6af58e899 100644
--- a/cpu/cc26xx-cc13xx/lpm.c
+++ b/cpu/cc26xx-cc13xx/lpm.c
@@ -244,8 +244,18 @@ lpm_drop()
 
   uint32_t domains = LOCKABLE_DOMAINS;
 
+  /* Critical. Don't get interrupted! */
+  ti_lib_int_master_disable();
+
+  /* Check if any events fired before we turned interrupts off. If so, abort */
+  if(process_nevents()) {
+    ti_lib_int_master_enable();
+    return;
+  }
+
   if(RTIMER_CLOCK_LT(soc_rtc_get_next_trigger(),
                      RTIMER_NOW() + STANDBY_MIN_DURATION)) {
+    ti_lib_int_master_enable();
     lpm_sleep();
     return;
   }
@@ -261,30 +271,20 @@ lpm_drop()
     }
   }
 
-  /* Check if any events fired during this process. Last chance to abort */
-  if(process_nevents()) {
-    return;
+  /* Reschedule AON RTC CH1 to fire just in time for the next etimer event */
+  next_event = etimer_next_expiration_time();
+
+  if(etimer_pending()) {
+    next_event = next_event - clock_time();
+    soc_rtc_schedule_one_shot(AON_RTC_CH1, soc_rtc_last_isr_time() +
+                              (next_event * (RTIMER_SECOND / CLOCK_SECOND)));
   }
 
   /* Drop */
   if(max_pm == LPM_MODE_SLEEP) {
+    ti_lib_int_master_enable();
     lpm_sleep();
   } else {
-    /* Critical. Don't get interrupted! */
-    ti_lib_int_master_disable();
-
-    /*
-     * Reschedule AON RTC CH1 to fire an event N ticks before the next etimer
-     * event
-     */
-    next_event = etimer_next_expiration_time();
-
-    if(next_event) {
-      next_event = next_event - clock_time();
-      soc_rtc_schedule_one_shot(AON_RTC_CH1, soc_rtc_last_isr_time() +
-          (next_event * (RTIMER_SECOND / CLOCK_SECOND)));
-    }
-
     /*
      * Notify all registered modules that we are dropping to mode X. We do not
      * need to do this for simple sleep.