On 12/17/2012 09:14 AM, Tim Niemeyer wrote:
Am Samstag, den 15.12.2012, 13:04 +0100 schrieb Gilles Chanteperdrix:
The latest Adeos is the core-3.4 branch from the git.denx.de/ipipe.git
repository, not the 'for-core-3.4' branch from the
git.xenomai.org/ipipe-gch.git.
Ah, thanks for clearing up.
Anyway, you can not use Xenomai 2.6.1 with linux 3.4, you also have to
use xenomai from its git repository git.xenomai.og/xenomai-2.6.git
It's working here fine. Why do you expect, that Xenomai 2.6.1 and linux
3.4 won't work together?
You could run into subtle bugs, but the only things which were fixed
probably only mattered if you enable the posix select syscall, and on
ARM multi-processor machines. So, if it compiles, it should run...
However, with the current xenomai git, you can build both kernel and
user-space in thumb mode and get lower latencies.
I'm using 'for-core-3.4' branch from git.xenomai.org/ipipe-gch.git with
Linux 3.4.14. I just build a big diff from 'for-core-3.4' against 3.4.6
and applied this on my 3.4.14. Then i took all the kernel-src files and
Kconfig changes from xenomai-2.6.1.tar.bz2 and build again a patch.
I use simple patches as they are easier for me to maintain in ptxdist.
While hunting a gpio-irq latency i tried to understand the adeos chained
How high a latency are we talking about?
The latency was about ~11µs. I then found out, that the cpu clock wasn't
the full 600MHz. I changed this and now the gpio-irq latency is about
~7µs. In contrast, the timer-irq latency is less than 3µs.
But when i use IPIPE_IRQF_NOSYNC the gpio-irq latency rises to ~14µs.
But on the other hand the switch between gpio-irq and timer-irq is
faster with IRQF_NOSYNC. It takes ~3µs and without IRQF_NOSYNC is takes
~7µs.
Yes IRQF_NOSYNC adds a bit to the latency, but the "immediate
dispatching" may leave the parent irq line masked for a whole
multiplexed gpio bank, and induce latencies in the millisecond range.
After several iteration, the current solutions seems the simplest which
actually work. Demultiplexed GPIO already have a high latency anyway
(and I doubt you really get a 3us, 7us or 11us latency on an omap, under
load, you probably get something more like 20 or 30us).
--
Gilles.
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