[GitHub] [incubator-nuttx] patacongo commented on a change in pull request #1380: [DRAFT] arch/stm32f7: Fixes bug in tickless driver where the compare register…

[GitBox <gi...@apache.org>]

patacongo commented on a change in pull request #1380:
URL: https://github.com/apache/incubator-nuttx/pull/1380#discussion_r451161696



##########
File path: arch/arm/src/stm32f7/stm32_tickless.c
##########
@@ -988,22 +988,31 @@ int up_timer_start(FAR const struct timespec *ts)
 }
 #endif
 
+#ifdef CONFIG_SCHED_TICKLESS_ALARM
 int up_alarm_start(FAR const struct timespec *ts)
 {
   uint64_t tm = ((uint64_t)ts->tv_sec * NSEC_PER_SEC + ts->tv_nsec) /
                 NSEC_PER_TICK;
-  uint64_t counter = ((uint64_t)g_tickless.overflow << 32) |
-                     STM32_TIM_GETCOUNTER(g_tickless.tch);
-
-  g_tickless.last_alrm = tm;
+  irqstate_t flags;
 
-  int32_t diff = tm / NSEC_PER_TICK + counter;
+  flags = enter_critical_section();
 
   STM32_TIM_SETCOMPARE(g_tickless.tch, CONFIG_STM32F7_TICKLESS_CHANNEL, tm);
 
   stm32_tickless_ackint(g_tickless.channel);
   stm32_tickless_enableint(CONFIG_STM32F7_TICKLESS_CHANNEL);
 
+  g_tickless.pending = true;
+
+  uint64_t counter = ((uint64_t)g_tickless.overflow << 32) |
+                     STM32_TIM_GETCOUNTER(g_tickless.tch);

Review comment:
       If an overflow from the LS to MS occurs, the fetched value will be wrong.  I usually do this (which does not require disabling interrupts):
   
       uint64_t counter;
       uint32_t ms1;
       uint32_t ms2;
       uint32_t ls;
       
       do
         {
           ms1 = get_ms()
           ls  = get_ls();
           ms2 = get_ms()
         }
       while (ms1 != ms2);
       
       counter = (ms1 << 32) | ls;
   
   Note aslo that declarations with code is not c89, but that is not so important in MCU-specific code.




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org