Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!apple!oliveb!amdahl!kevin
From: kevin@uts.amdahl.com (Kevin Clague)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Introduction to comp.sys.amiga.tech
Message-ID: <08BrO8cS3A1010LJrFA@amdahl.uts.amdahl.com>
Date: 8 Mar 89 15:39:16 GMT
References: <1739@psu-cs.UUCP>
Reply-To: kevin@amdahl.uts.amdahl.com (Kevin Clague)
Organization: Amdahl Corporation,  Sunnyvale, CA 94086
Lines: 59

In article <1739@psu-cs.UUCP> bartonr@psu-cs.UUCP (Robert Barton) writes:
>> # 4 : The Amiga's custom graphics and sound chips can only access the
>> first 512K of memory (slow or chip memory). Therefore, anything that
>> these chips use must be in the first 512K of memory. This includes
>> Window, Gadget and BitMap structures that Intuition uses. To make sure
>> that you get chip memory do add the MEMF_CHIP constant to your call to
>> malloc:
>>
>>       foobar *milkchocolate;
>>       milkchocolate = ( foobar * ) AllocMem (sizeof(foobar), MEMF_CHIP);
>>
>> Then copy your data to the memory pointed to by "milkchocolate". 
>>
>> Edwin Hoogerbeets
>> uunet!utai!utcsri!hcr!edwin
>
>  This is a new one to me.  When the OpenWindow() routine allocates the
>memory for the Window structure it asks for MEMF_CLEAR | MEMF_PUBLIC.  Same
>with OpenScreen() when allocating a Screen or RasInfo structure.  Since a
>Screen contains a ViewPort, a RastPort, a BitMap, and a LayerInfo this
>implies that none of these structures need to be in chip memory either.

It is true that things the custom chips need to access need to be in CHIP
RAM.  The "art" or hard part is knowing which things the custom chips
actually access.  Example:

 Bit planes need to be in CHIP RAM, but RastPort and Window structures
do not.  The 680X0 access these higher level structures, and eventually
calls the custom chips to actually manipulate data in your viewport or
screen's bitmaps.

 Here is a list of the places where some of the resources should be
placed (I wish I had RKM's here at work):

  CHIP RAM        NOT CHIP RAM
  ________        ___________
  BitPlanes       BitMap structure
                  RastPort structure
                  LayerInfo structure
                  Window structure
                  NewWindow structure
                  Screen structure
                  NewScreen structure
                  ViewPort structure
  BitPlanes       Image structure
                  Border structure

So you see that really very few things actually need to be in chip RAM.
I hope this helps.

Kevin
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[  Any thoughts or opinions which may or may not have been expressed  ]
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