High-resolution timers on AT91SAM9G45

[jan.weil at web.de]

Hi,

I am currently trying to achieve latency < 1 ms (~ 10 us would be great) on
this board

<http://www.ic-board.de/product_info.php?info=p105_ICnova-SAM9G45-OEM.html>

running Linux 2.6.33.2 with a couple of patches provided by the company to
support their evaluation board.

I reconfigured CONFIG_AT91_TIMER_HZ=1024, which results in a jiffy of ~ 1
ms, which is a good start, but I am not quite there yet.

These patches

<http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-03/msg01396.html>

along with the post by maddis from 03. April 2009 in this thread

<http://www.at91.com/forum/viewtopic.php/f,12/t,4194/>

made me believe that it might be possible to activate high-resolution
timers and make the kernel preemptible on this controller, so I
reconfigured:

CONFIG_PREEMPT=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_ATMEL_TCLIB=y
CONFIG_ATMEL_TCB_CLKSRC=y
CONFIG_ATMEL_TCB_CLKSRC_BLOCK=0

However, booting up the new kernel I noticed the following line:

atmel_tcb: probe of atmel_tcb.0 failed with error -22

and /proc/timer_list looks like this:

Timer List Version: v0.5
HRTIMER_MAX_CLOCK_BASES: 2
now at 54883789537 nsecs

cpu: 0
 clock 0:
  .base:       c03e6014
  .index:      0
  .resolution: 976559 nsecs
  .get_time:   ktime_get_real
  .offset:     0 nsecs
active timers:
 clock 1:
  .base:       c03e6040
  .index:      1
  .resolution: 976559 nsecs
  .get_time:   ktime_get
  .offset:     0 nsecs
active timers:
 #0: <c7a95f30>, hrtimer_wakeup, S:01
 # expires at 55787857570-55787907570 nsecs [in 904068033 to 904118033
nsecs]
  .expires_next   : 2147483646999999999 nsecs
  .hres_active    : 0
  .nr_events      : 0
  .nr_retries     : 0
  .nr_hangs       : 0
  .max_hang_time  : 0 nsecs
  .nohz_mode      : 0
  .idle_tick      : 0 nsecs
  .tick_stopped   : 0
  .idle_jiffies   : 0
  .idle_calls     : 0
  .idle_sleeps    : 0
  .idle_entrytime : 54880519167 nsecs
  .idle_waketime  : 0 nsecs
  .idle_exittime  : 0 nsecs
  .idle_sleeptime : 52111282391 nsecs
  .last_jiffies   : 0
  .next_jiffies   : 0
  .idle_expires   : 0 nsecs
jiffies: 4294716297


Tick Device: mode:     0
Per CPU device: 0
Clock Event Device: pit
 max_delta_ns:   0
 min_delta_ns:   0
 mult:           35791392
 shift:          32
 mode:           2
 next_event:     2147483646999999999 nsecs
 set_next_event: <(null)>
 set_mode:       pit_clkevt_mode
 event_handler:  tick_handle_periodic

And running cyclictest <https://rt.wiki.kernel.org/index.php/Cyclictest>
confirms that high-resolution timers are still not available.

Does anyone happen to have a clue what might be the reason for the
atmel_tcb error mentioned above and what I could try next?

Thanks for your attention.

Best,

Jan