comp.arch.embedded Google Group

Re: choosing an scheduling algorithm for a RTOS

j...@infinitefactors.org (Jon Kirwan) — Sun, 11 Nov 2009 20:16:42 UT

On Sun, 08 Nov 2009 10:58:09 +0000, FreeRTOS info <noem...@given.com>
wrote:
I'm pretty sure this is a student question.
I've taught these classes before -- Operating Systems and Concurrent
Programming, for example. And at my university, these are typically
2nd year classes for CS students. This framing of the question is

Re: Time

zwsdot...@gmail.com (larwe) — Sun, 11 Nov 2009 20:03:18 UT

Not at all. MET is not TOD. And you have not, in your little
discourse, defined absolute rules about what "now" or "an hour from
now" means. I might be sitting at my desk in NY at 0700 local TOD,
making an appointment to meet you in CA at 1700 local TOD; I certainly
don't mean "ten hours from NOW", I mean 13 hours from my current NOW,

Re: Time

not.going.to...@seen.com (D Yuniskis) — Sun, 11 Nov 2009 20:06:06 UT

The executable may not be available, etc. Yes, there
are ways around this. E.g., create wrappers for those
things that aren't available, ensure the wrappers are
*always* available and have *them* keep getting
"reawakened" periodically *or* in response to an
event that satisfies their prerequisites (e.g., "SD

Re: Time

not.going.to...@seen.com (D Yuniskis) — Sun, 11 Nov 2009 19:45:00 UT

Exactly.
Of course! If I am flashing a lamp a 1Hz, I don't keep
setting alarms for "now+1sec".
Yes. The problem lies in how you communicate this to
the user (i.e., how you ascertain the *user's* idea
of whether he is thinking in relative or absolute terms).
Generally, I don't ask users questions. Instead, I try to

Re: What coding standard are you using for C?

not.going.to...@seen.com (D Yuniskis) — Sun, 11 Nov 2009 19:26:32 UT

<grin> *I* used to think that way! I kept backups on
external SCSI drives that were neither "on-line" (mounted)
nor *spinning* (powered up).
On one occasion, I needed to restore a file from one of these
"offline archives". I spun-up the drive, mounted the filesystem
and the drive *crashed*!
OK, bad luck.

Re: What coding standard are you using for C?

david.br...@hesbynett.removethisbit.no (David Brown) — Sun, 11 Nov 2009 18:53:58 UT

You /can/ lose data on hard disks fairly quickly, but typically you have
to be very unlucky (assuming you make your backups write-protected for
normal use). It's a good idea to have two independent copies on
different computers, in different locations - you are not going to have
hard disk fails, fires, or human error on both systems at once.

Re: Time

mborger...@comcast.net (Mark Borgerson) — Sun, 11 Nov 2009 18:36:23 UT

In article <hd6o16$fg...@aioe.org>, not.going.to...@seen.com says...
IMHO, people think about time in two ways: As intervals
and as absolute date/time occurences. Absolute times can
be both near and far in temporal distance---as near as the
starting time for a televised football game that will begin

Re: Time

not.going.to...@seen.com (D Yuniskis) — Sun, 11 Nov 2009 17:16:50 UT

POSIX *used* to allow for *double* leap seconds. I think
that capability has been removed.
Note that leap seconds can also *subtract* a second (though
this has never? happened)
*All* "human formatted" time schemes are PITAs for machines.
The only realistic way to track time is just to count seconds.

Re: mmap returning MAP_FAILED

pfeif...@cs.nmsu.edu (Joe Pfeiffer) — Sun, 11 Nov 2009 17:09:56 UT

That would do terrible things to the utility of shared memory -- no,
MAP_SHARED and PROT_WRITE are compatible. Maybe you're thinking of
MAP_SHARED and MAP_ANONYMOUS (which didn't used to be compatible, but is
since 2.4).

Need help from programming masters (USB hub)

joseph...@yahoo.com (dzone007) — Sun, 11 Nov 2009 17:07:46 UT

Hi guys!
I am just wondering if you could give some codes regarding the operation of
the USB hub. Since a USB host is capable of communicating to a single
device, I was thinking of using the USB hub as the device. The
communication is from HOST to HUB. However, I need a piece of code to
communicate to the hub to enumerate it and learn about physical bus events

Re: Use of MAX232 as power supply for operational amplifier in 5V powered system?

andr...@sdf.lonestar.org (Andrew Smallshaw) — Sun, 11 Nov 2009 16:59:46 UT

I like it because it is dirt cheap. Last time I needed fairly
small quantities of an RS232 driver the ST232 was 70-odd pence a
peice. The MAX232 was around four or five times that as I remember.
That's a big premium simply for the brand name genuine part.

Re: Time

not.going.to...@seen.com (D Yuniskis) — Sun, 11 Nov 2009 17:05:28 UT

My point is that by *defining* system time to be a monotonically
increasing, unresetable function, you *can* make this assumption
for "system times". I.e., if you look at the system time
at any arbitrary time, T1, and then look at it at *any*
arbitrary time thereafter, T2, you *know* that T2 > T1.
By definition. :>

Re: Time

andr...@sdf.lonestar.org (Andrew Smallshaw) — Sun, 11 Nov 2009 16:39:05 UT

Many, many bugs have been caused by this kind of assumption.
Perhaps the most notable example is the lbolt variable inside
traditionally structured Unix kernels. I'm most familiar with it
from dealing with SCO Unix in the past but ISTR it affected other
systems too, mostly with third party drivers where the develpers

Re: Time

keina...@sci.fi (Paul Keinanen) — Sun, 11 Nov 2009 16:35:04 UT

On Sun, 08 Nov 2009 08:27:02 +0000, Paul E Bennett
The UTC is not a linear time scale due to the leap seconds that are
added at random intervals (3, 6, 9, 12, 15 .. month) due to the
slowing down of the rotation of the Earth. When the leap second is
added, the clock should count 23:59:59, 23:59:60, 00:00:00 ....

Re: Software real time clock using timer unit

bbew...@mapson.nozirev.ten (Rich Webb) — Sun, 11 Nov 2009 16:25:38 UT

On Sun, 08 Nov 2009 09:35:23 -0600, "alex99" <alex.xande...@gmail.com>
wrote:
Decide on a useful interval. For a human-space display, a 1 Hz update is
plenty. Then, given your device's clock, PLL setting, and peripheral
clock divider, select a prescaler and match register pair that results
in a 1 Hz event. Set the timer's control registers appropriately and,