Re: Kernel Oops

Paolo Mantegazza <[email protected]>
Newsgroups gmane.linux.real-time.rtai
Message-ID <VI1PR06MB14710AEEE4827DF6913FFF0490980@VI1PR06MB1471.eurprd06.prod.outlook.com>
Unfortunately this thread went on privately. Likely because of a wrong answer click of mine, apologies. 

In any case it gives me the chance of remarking a few things related to the support of Linux-3.x.x and now 4.x.x.
- RTAI-4 onward) is based on the oneshot mode timing only. I still use periodic timers on data acquisition card to time specific tasks . whituout charging the scheduler with their pacing.
- from RTAI-5, i.e the actual VULCANO to be released shortly,  there starting/stopping_rt_timer, it is done by rtai_sched onyhow.
- in such a view the setting of the hard timer mode its start/stop, both in periodic and oneshot mode, will do nothing; they are just kept for compatibility, so that there is no need to change any existing code
- HPET is not used by RTAI but 8259/54 is used in UP mode, even if it is strongly suggested to enable the APIC if available
- RTAI does not use the second channel of 8259/54 to emulate a continuously running clock, so  a _TSC_is_needed

In practice what above restricts the newest RTAI versions to true 586s and onward. For fake 586s and 486 earlier version of RTAI should be used.

That said there is no need to disable NO_HZ and high precision/resolution timers if they are available in Linux.

Paolo

________________________________________
From: Rtai [[email protected]] on behalf of Alec Ari [[email protected]]
Sent: Wednesday, March 30, 2016 10:37 PM
To: RTAI Mailing List
Subject: Re: [Rtai] Kernel Oops

RTAI should be able to use the 8259/8254 timers unless that's now broken? It's never _needed_ APIC or HPET in the past. If it's broken or not working (buggy hardware / BIOS) try disabling high precision + high resolution event timers in kernel config and BIOS if applicable. Also, to avoid NULL pointer issues, set CONFIG_LSM_MMAP_MIN_ADDR to value 65536.

Alec Ari
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