Re: [Xenomai-help] [Ethercatmaster-users] EML conflict with RTCAN? low_level_input framebuilding failed.

[Wolfgang Grandegger <wg@domain.hid>]

Roland Tollenaar wrote:
> Hi,
> 
> Some more interesting findings (no i-pipe trace yet though).
> 
>> Hmm, this doesn't convince me yet. Such skews during startup may as well
>> be triggered by unusual load during runtime (non-RT activity or new RT
>> components). Did you put your system under adequate non-RT load as well
>> while measuring the outputs?
> Running latencytest with my application shows an average latency of 
> about 40 and a max of 200ns. This was rather shocking so I turned off 
> rtcan in my application. Now the max latecy is 60ns. Turn off EML and 
> turn on rtcan, max latecy is 230ns. How is that for strange? But since I 
> can see the scope output bobbing with 200ns during the latency test, I 
> can also see that if I run my application without the latency test the 
> huge max latency disappears entirely. Maybe it is time for the trace but 
> then again I am still using CAN over the parallel port so will see what 
> it does on a machine with a PCI CAN adaptor first. Because I think I 
> know what happens: Due to the external loading the CAN recv interrupt 
> triggers the Rx ISR briefly before the 1ms task period ends. Due to the 
> priority of the ISR (huge debate over this) and its atomicness (if I 
> remember correctly) the reading out of the slow hardware delays the 
> start of the new task period.
> 
> Just thought it was interesting to mention. Btw when the latency appears 
> there are no overflow messages or anything like that which support the 
> theory I have about the cause.
> 
> Btw2 the 200ns latency spikes do not cause the scope to loose lock on 
> the saw-tooth so whatever causes that problem is of a different nature 
> still.

s/ns/us/ ?

Wolfgang.