IRIS status

Bas Wijnen wijnen at debian.org
Mon Feb 15 10:09:27 EST 2010


On Sat, Feb 13, 2010 at 09:12:21AM -0500, Carlos Camargo wrote:
> Hi I'm thinking in use Iris or eCos on SAKC, Iris have Real Time support?
> How many peripherals support Iris? Iris is ready  for commercial
> applications?

Hi,

I've been hesitating to suggest this, but considered Iris to be not
finished enough.  Plus I am likely to not spend much time on the
real-time support myself, so someone else would have to do that (if more
is required than what I'm describing below; it may well be sufficient).

Note however that there is currently no port of libc/libstdc++ for Iris.
That shouldn't be a big problem.  I find it quite easy to work without
it.

For the implementation of proper real-time support, I think all that is
required is a priority scheduler.  Currently the scheduler is pretty
random about which task to schedule.  I want to implement priority
levels.  A thread at a higher priority will always run, as much as it
wants to, before a thread of a lower priority.  This is not like nice
levels, which determine the ratio of time slices.

In practice, you will want to set interrupt handlers to a high priority,
meaning that they will always be scheduled immediately when an interrupt
is received.

This approach does not support reserving a certain amount of processor
time for a certain thread (for example, 30% for the gpio handler, 30%
for the usb device handler and 40% for all others; if no gpio or usb
device thread wants to run, the cpu time is thrown away).  I don't think
this should be a problem, but if you think it is, I think it may be
tricky to solve (and I'm not really interested in putting much time into
it).

Summarizing: it all depends on what you want to do.  There currently is
no priority scheduling, but that should be implemented anyway.  With
that available, it is possible to always immediately handle interrupts,
and have priority threads be running immediately when an alarm they set
goes off.  If this is what you mean with "real-time support", I think it
should be able to do that.

If you can give some details about what you want to do, I can see if
there are things that Iris is not capable of.

Thanks,
Bas
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