Hi, 2012/5/10 Grant Edwards <grant.b.edwards@xxxxxxxxx>: > On 2012-05-09, Joachim Achtzehnter <joachima@xxxxxxxxxxxxxx> wrote: >> Grant Edwards wrote: > Unfortunately, the requirements are a bit fuzzy -- I've got an ISR > deadline of about 20us that I'm trying to meet [I wouldn't mind a > little chat with the person who designed _that_ requirement into the > hardware]. What I don't know is how hard that deadline is. With the > RT patch (and without IRQF_NODELAY), I miss the deadline most of the > time (I'd guess about 80% of the time). > > Without RT or with RT and IRQF_NODELAY, it looks like I meet the > deadline maybe 98% of the time (under test conditions). What I don't > know is if once the deadline is missed it matters weather it's missed > by 50us or by 250us [or if 98% is going to be anywhere close to > acceptible, for that matter]. Given my experience with these cores and the RT patch: This 20usec is too close. There are some places in the code that have interrupt disable section of about 30usec (also process ctx-switch cache flush have high impact) So, I expect you will not get this very robust. If the 20usec requirement is hard, you can also look at using an FIQ. Kind regards, Remy -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
