Re: ADA task

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

Samuel T. Harris <u61783@gsde.hso.link.com> wrote in article
<323B1F23.2781@gsde.hso.link.com>...

> Every compiler will have a fidelity of delay it can support.
> On our SGI systems, both VADS and GNAT support a 0.01 second delay
> fidelity. Delays command to be less than 0.01 seconds are actually
> 0.01 seconds. This is not acceptable to high fidelity harmonic
> simulations involving a least common multiple rate of greater
> than 100 hertz. If no compiler supports the required fidelity,
> then replacing the compiler is not really a viable option.
> 
You're right about VADS on SGI "out of the box".  However, we (Hughes
Aircraft -- Huntsville, AL) run our process which needs higher-fidelity
delays at non-degrading priority 39 (IRIX 5 & 6), with the fast_Hz clock
set to 2 KHz.  You may also need to change v_usr_conf_b.a (I don't remember
off the top of my head) to reduce that 10 ms. fudge factor to 0.  We have
found worst-case infidelity of 2-3 ms. on a heavily-loaded (development)
machine, but typically under 500 micro-sec., as would be expected.  The Ada
run time gets to check for expired delays usually every 500 micro-sec.
Normally to get priority 39, you have to run with super-user privileges,
but we reconfigured the kernel to allow just the one priority level (the
lowest level using the Fast_Hz clock instead of the 10 ms. sginap) to be
run by users.  Since most don't care enough to find out how to run at that
priority, generally only the "official" executables needing RT priority run
this way.
-- 
David C. Hoos, Sr.,
http://www.dbhwww.com
http://www.ada95.com