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Date: Sun, 06 Jul 2014 14:50:43 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai] issue with cobalt/timer: avoid periodic timer drift
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To: Matthias Schneider <ma30002000@yahoo.de>, "xenomai@xenomai.org" <xenomai@xenomai.org>

On 07/06/2014 11:48 AM, Matthias Schneider wrote:
> Hi all,
>
> commit
>
> 2014-06-02 c20fceb147e337e2379b29ecd81b943318c7fbc7
> (patch) cobalt/timer: avoid periodic timer drift
>
> seems to cause an endless kernel loop in one of my
> freertos demos. The issue does not occur when
> reverting this commit.
>
> Investigating the issue, can see the following:
>
> #0  0xc00ba45c in mach_arm_nodiv_llimd (rhs_integ=<optimized out>, frac=<optimized out>, op=<optimized out>)
>      at arch/arm/xenomai/include/asm/xenomai/uapi/arith.h:120
> #1  xnclock_core_ns_to_ticks (ns=0) at kernel/xenomai/clock.c:52
> #2  0xc00baf34 in xnclock_ns_to_ticks (clock=<optimized out>, ns=<optimized out>)
>      at include/xenomai/cobalt/kernel/clock.h:204
> #3  xntimer_update_date (timer=0xde706518) at include/xenomai/cobalt/kernel/timer.h:268
> #4  xnclock_tick (clock=0xc06b1138 <nkclock>) at kernel/xenomai/clock.c:644
> #5  0xc00bcbcc in xnintr_core_clock_handler () at kernel/xenomai/intr.c:121
> #6  0xc0095a98 in dispatch_irq_head (irq=<optimized out>) at kernel/ipipe/core.c:1179
>
> This seems to be the endless loop:
> 642                     do {
> 643      timer->periodic_ticks += interval_ticks;
> 644      xntimer_update_date(timer);
> 645                     } while (xntimerh_date(&timer->aplink) < now + clock->gravity);
>
> gdb) info locals
> timerq = 0xdebdae98
> now = 4257712977
> interval_ticks = 0
> timer = 0xde706518
> delta = <optimized out>
> h = 0xde706518
>
> (gdb) print *timer
> $1 = {
>    aplink = {
>      link = {
>        next = 0x100100,
>        prev = 0x200200
>      },
>      key = 0,
>      prio = 999999999
>    },
>    adjlink = {
>      next = 0x0 <__vectors_start>,
>      prev = 0x0 <__vectors_start>
>    },
>    status = 1,
>    interval = 0,
>    interval_ns = 0,
>    periodic_ticks = 0,
>    start_date = 0,
>    pexpect_ticks = 0,
>    sched = 0xc06b1610 <nksched>,
>    handler = 0xc00c7dc4 <timeout_handler>,
>    name = "CREATOR", '\000' <repeats 24 times>,
>    handler_name = 0xc05ad429 "timeout_handler",
>    next_stat = {
>      next = 0xde706624,
>      prev = 0xde705c24
>    },
>    scheduled = {
>      counter = 3
>    },
>    fired = {
>      counter = 1
>    }
> }
> (gdb) print *clock
> $2 = {
>    wallclock_offset = 200209,
>    resolution = 1,
>    gravity = 140,
>    name = 0xc05ac815 "coreclk",
>    timerdata = 0xdebdae98,
>    id = -1,
>    vfile = {
>      entry = {
>        pde = 0xde1b8700,
>        file = 0x0 <__vectors_start>,
>        lockops = 0xc06b2c20 <xnvfile_nucleus_lock>,
>        refcnt = 0,
>        private = 0xc06b1138 <nkclock>
>      },
>      privsz = 4,
>      datasz = 104,
>      tag = 0xc06b117c <nkclock+68>,
>      ops = 0xc06b1120 <vfile_clock_ops>
>    },
>    revtag = {
>      rev = 36
>    },
>    statq = {
>      next = 0xc06b18d4 <nksched+708>,
>      prev = 0xde706e24
>    },
>    nrtimers = 24
> }
>
> Does anyone see right away what is going on wrong
> or shall I continue investigating the issue?
>

Assuming timer->interval_ns can't be null as the timer is deemed 
periodic, there must be something wrong with how the elapsed count of 
periodic ticks is tracked. Gilles will likely have a look at this when 
time allows.

-- 
Philippe.