Hi:
At 07:44 AM 26-04-99 -0600, you wrote:
>On Mon, Apr 26, 1999 at 08:44:25AM -0400, Pierre Cloutier wrote:
>> Then I discovered RTAI with more or less the same stuff built-in the
>> scheduler - and the prospect of implementing the QNX primitives without
having
>> the software look like a burger king sandwich :-)
>
>This points to a design objective difference between RTAI, as I understand
>it, and RTL. To put QNX primitives into RTL you need to either layer on top
>of the standard scheduler objects or rewrite the standard scheduler objects.
>In RTL, we are not willing to make semaphores or semaphore overhead a
>mandatory part of the kernel.
I think you sacrifice much "elegance" for the overhead of a few if's but
I'll comment more on this when I better understand the guts of the Real
Time implementations.
>
>> control objects. I'm also looking at other odds and ends like connectivity
>> with existing QNX arcnet networks (I have a whole bunch of customers who
>> are arcnet wired).
>
>Re your earlier arcnet question. Why is the "dual ported memory" in this
>fixed location? Is that a hardware requirement or is it a dos legacy?
Back in the early 80's an IBM designer figured that a PC with the
capability to address 16 "cores" would have plenty of memory. Further, the
same
designer reasoned that the trouble and pain of dealing with segments would
be soon forgotten. Since INTEL had bothered to put all these address lines
around the chip, the area above the DRAM was assigned to gadgets like CGA
color controlers, the BASIC ROM, and what the heck, the infamous BIOS etc.
Too lazy to write a decent operating system for their newborn, the IBM
folks subcontracted the OS to a small unknown firm :\
The small firm did not pay attention to memory because memory prices where
coming down and INTEL was adding more address lines around the chips.
Soon they busted the 640K limit - despite the segmentation problem and much
pain. They jumped over the 1024K mark and entered the worm hole of expanded
memory. Other folks who by then had evolved to protected mode suffered when
came the time to buy memory boards.
To this date, the area between the 640K and 1024K marks remains prized real
estate for add-on boards...
>
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>
_______________________________________________________
Pierre Cloutier
Tel: (450)-659-9186
Fax: (450)-659-0014
POSEIDON CONTROLS INC
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For more information on Real-Time Linux see:
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