Fw: Re: Real time?

[shackle <shackle-at-cme.nist.gov>]

--- Forwarded Message ---
 From: shackle <shackle-at-cme.nist.gov>
 To: shackle <shackle-at-cme.nist.gov>
 Sent: 25 Sep 2000 10:09:07 EDT
 Subject: Re: Real time?


On Mon, 25 Sep 2000 10:02:47 -0400, emc-at-nist.gov said:

> 
>  
>  
>  My 2 cents worth on QNX.
>  
>  There is another factor that might prevent porting of EMC to  QNX, or another
>  RTOS for embedded applications. That parameter is the schuduling resolution. 
>  Under Linux, another unix-like commercial real-time operating system, a couple

I meant   Lynx not Linux. 




>  of years ago the best scheduling resolution we could get was 5 milliseconds.
>  Under VxWorks, a not very unix-like commercial RTOS, the best I could get was
>  500 microseconds.  I haven't seen anything that compares with the 15
>  microseconds that RTlinux can deliver.
>  
>  The main reason is that RTLinux allows a lot less flexibility and provides
>  fewer functions to real-time application programmers  than those commercial
>  systems. In those RTOS's "real-time" programs can read/write files,
>  send/recieve data over a network and  dynamically allocate/deallocate  memory.
>  (Although programmers need to be extremely careful when doing these things or
>  the program will no longer be deterministic.) In RTLinux, you can't do any of
>  these at all. This might be a good thing, just to prevent errors. But it has
>  also allowed RTLinux to get much better scheduling resolution.
>  
>  Does anybody happen to know what kind of scheduling resolution is possible
>  under QNX? I couldn't find the info on their web page.
>  
>  -- Will
>  
>  
>  
>  
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>  

-- 
-------------------------------------------------
William Penn Shackleford III			shackle-at-nist.gov
National Institute of Standards & Technology	Tel:	(301) 975-4286
100 Bureau Drive Stop 8230			FAX:	(301) 990-9688
Gaithersburg MD  20899	USA
http://www.isd.mel.nist.gov/personnel/shackleford/
Office Location: Bldg. 220 Rm A253 




-- 
-------------------------------------------------
William Penn Shackleford III			shackle-at-nist.gov
National Institute of Standards & Technology	Tel:	(301) 975-4286
100 Bureau Drive Stop 8230			FAX:	(301) 990-9688
Gaithersburg MD  20899	USA
http://www.isd.mel.nist.gov/personnel/shackleford/
Office Location: Bldg. 220 Rm A253