[net.micro.amiga] Questions about Rumors

aic@pucc-i (Craig Norborg (aka Doc Pierce)) (11/15/85)

  Amiga,

   I have just finished talking to the dealer I bought my Amiga from
and heard some interesting rumors and such from him.  He was talking to
some of your engineers who frequent CompuServe and they were telling
him that if you get the ram that goes over the first 512K boundry, such
as the Tecmar board, that the ram will actually run 2 times faster than
that in the first 512K!  From what I have understood, the machines
first 512K was supposed to hold the fastest ram, which is true?  What
will be the advantages/disadvantages to getting the extra 512K?

    Also, could you confirm/deny the possiblity of substituting the
68000 contained within the machine with a 68010?  Will this hurt or
improve the machines speed, and is it possible?

     Once again, for those of us who have already bought Amiga's, could
you state the company policy for hardware/software updates?

		Thanx in advance,
-- 
					Craig Norborg (aka Doc Pierce)
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hr@uicsl.UUCP (11/17/85)

Someone referred to the Tecmar board and the external memory.
Does anyone know when it will be available? And for how much?

For that matter, has ANY 3rd party option hit the market yet?

						harold ravlin
					{ihnp4,pur-ee}!uiucdcs!uicsl!hr

bobp@amiga.UUCP (Robert S. Pariseau) (11/17/85)

The speed of RAM placed on the expansion bus depends, to some extent,
upon the quality of it's implementation.  The Amiga architecture ALLOWS
expansion bus memory (that is memory over the first 512K) to run at
full bus speeds.  I don't know of anyone implementing expansion bus
memory who expects to provide slower memory -- but you never know.

The first 512K of memory, known as Chip memory to the AllocMem()
function, is the only memory the custom chips can get to.  It is
possible to configure your Amiga such that the bandwidth out of
chip memory is largely consumed for video display.  In this high
data rate mode of operation, the 68000 yields to the higher priority
needs of the system DMA channels such as the video.  This is called
memory "contention".  [For newcomers:  There is NO contention in
the 320x200, 16 color mode normally used for games, or in the
640x200, 4 color mode normally used for Workbench and text functions.]

There can NEVER be contention in the Writeable Control Store (where the
system firmware is kept) or in the expansion bus memory [ignoring, of
course, any contention BUILT-IN to stuff on the expansion bus].  For
this reason, the AllocMem() function identifies expansion bus memory
as Fast memory.  Note that Fast memory can NEVER be faster than Chip
memory in the no-contention modes of operation.

As a programmer, you need to be sure that data structures you make
which are directly referenced by the custom chips are allocated in
Chip memory.  This means, don't statically allocate them, or place them
on the stack, since that may place them in Fast memory depending upon
what else is in the machine --> ergo, your programs stop working
when people add expansion bus memory.

For V1.0, you must dynamically allocate your Chip structures in Chip
memory -- moving data from your static structures as necessary.

For V1.1, the system loader recognizes flags in the program image
which say that certain portions of the program MUST be loaded into
Chip or Fast memory.  If a preference is not specified, then Fast
memory is generally used first -- maximizing system resources.  The
program flags can be set using the new Atom utility which is applied
to your object binary files BEFORE you link them with Alink.  [This
means you can set the flags on routines which are then placed in
libraries so that anyone can use your routines without having to
know special rules about where they can go.]  Note that you STILL
can not safely allocte Chip structures on the stack.

-----------------

Commodore can NOT recommend that you replace the 68000 in your
Amiga with any other processor.  This warning is brought to you
by our good friends at the FCC who insist that we test any hardware
configuration against Class B restrictions before we recommend it
to anyone.

That aside, we HAVE heard from folks who (in STRICT VIOLATION of their
warranty) have opened up their Amigas and replaced the processor.
Their reports say that the system software works fine unless you
have a buggy program that generates one of the 68000 exceptions that
changed for the 68010.  The trap catcher and the stuff that puts up
alerts and gets you into ROMWack is not prepared for the new-fangled
stack frame put out by a 68000.

Note that there is a routine called GetCC() in EXEC which gets you
your processor condition code in a manner that is compatable across
the 68000 family.  This is the only normal-operation incompatability
that needs to be addressed.