Re: [Xenomai-core] Problem with periodic timer on PPC40x solved

[Wolfgang Grandegger <wg@domain.hid>]

Niklaus Giger wrote:
> Am Montag, 25. September 2006 17:57 schrieb Philippe Gerum:
>> On Sun, 2006-09-24 at 23:07 +0200, Wolfgang Grandegger wrote:
>>> Niklaus Giger wrote:
> <..>
>> Ok, we can go for the lazy fix here, since this code is poised to
>> disappear anyway. I've merged a variant of the above we already use for
>> the ARM port, which scales down the period to microseconds instead of
>> losing precision on the count of timebase ticks per jiffy.
>>
>> - ticks = ns * tb_ticks_per_jiffy / (1000000000 / HZ);
>> + ticks = (ns / 1000) * tb_ticks_per_jiffy / (1000000 / HZ);
> Thanks for finding this solution. I tried to understand mulhwu and 
> mulhwu_scale_factor but couldn't figure out a correct solution in a short 
> time.

I took me also some time to understand the meaning. mulhwu(a,b) returns 
the high 32 bits (32..63) of a*b. A possible quick fix could be:

   if (mulhwu(ns, tb_ticks_per_jiffy) > 0)
	ticks = (ns / 1000) * tb_ticks_per_jiffy / (1000000 / HZ);
   else
	ticks = ns * tb_ticks_per_jiffy / (1000000000 / HZ);

But Philippe already applied a reasonable fix.

> 
> The buildbot cannot presently power on and off my PPC405 target board, as the 
> my power outlet switching device is broken and has been sent back for a 
> remplacement.
> 
> I did however run some tests manually and have the following questions about 
> the output:
> Why do I get negative values for latenciy values?
> Is the output of lines like "Xenomai: Switching display-3238 to secondary mode 
> after exception #1025 from user-space at 0x100033c4 (pid 3240)" harmless or 
> the result of a activated CONFIG_XENO_OPT_DEBUG<..> option?
> 
> Mon Sep 25 20:20:33 UTC 2006
> running: ./run -- -T 5 -t2 # latency
> *
> *
> * Type ^C to stop this application.
> *
> Xenomai: Switching display-3238 to secondary mode after exception #1025 from 
> user-space at 0x100033c4 (pid 3240)
> == Sampling period: 100 us
> == Test mode: in-kernel timer handler
> == All results in microseconds
> warming up...
> RTT|  00:00:01  (in-kernel timer handler, 100 us period, priority 99)
> RTH|-----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat worst
> RTD|      -5.108|      -4.754|      -0.905|       0|      -5.108|      -0.905
> RTD|      -4.963|      -4.871|       1.155|       0|      -5.108|       1.155
> Xenomai: Switching display-3238 to secondary mode after exception #1025 from 
> user-space at 0xfda9638 (pid 3240)
> RTD|      -4.963|      -4.758|      16.020|       0|      -5.108|      16.020
> RTD|      -6.313|      -4.861|      10.980|       0|      -6.313|      16.020
> Xenomai: Switching display-3238 to secondary mode after exception #1025 from 
> user-space at 0xfe7c1c4 (pid 3240)
> ---|------------|------------|------------|--------|-------------------------
> RTS|      -6.313|      -4.811|      16.020|       0|    00:00:05/00:00:05
> Xenomai: stopping RTDM services.
> 
> Best regards