On Thu, May 10, 2012 at 11:46:26AM +0200, Remy Bohmer wrote: > 2012/5/10 Grant Edwards <grant.b.edwards@xxxxxxxxx>: > >> 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). > > Given my experience with these cores and the RT patch: This 20usec is > too close. That's pretty much what I've decided. > 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. Does the normal AT91 kernel not use FIQs at all? If so, I might be able to dedicate the FIQ to this function and have it happen without the Linux kernel knowing about it (or affecting it). Any communication between it and a normal user-task would have to be handled carefully... -- Grant -- 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
