Allocating memory within a 64K boundary

deimos · 30 October 2019, 10:50

I need to allocate a chunk of memory that doesn't cross a 64K boundary, so that I can access it all with the same half of the address, so that I can update pointers within a copper list without worrying about them being half read when I do it.

Is there a smarter way to do this than by allocating 128K of memory and then just using part of it?

Can I return the bits that I don't want to use?

Samurai_Crow · 30 October 2019, 10:53

AROS has a way in its version but AmigaOS' Kickstart doesn't.

DanScott · 30 October 2019, 10:56

http://eab.abime.net/showthread.php?...t=64k+boundary

deimos · 30 October 2019, 11:13

Quote:

Originally Posted by DanScott

http://eab.abime.net/showthread.php?...t=64k+boundary

Thank you, that gives me exactly what I need.

ross · 30 October 2019, 11:57

In my examples, in fact, as you may have noticed, I have always taken for granted an allocation of the kind

Which one to choose between the two methods?

If you are not concerned about memory restraints, allocate x+65536.
If yes, the Alloc(x+65536), Forbid(), Free(), AllocAbs(), Permit() work well, but it fragment slightly the memory pool.

meynaf · 30 October 2019, 12:14

Doing FreeMem on partial block isn't recommended but in practice it works.

30 October 2019, 10:50	#1
deimos It's coming back! Join Date: Jul 2018 Location: comp.sys.amiga Posts: 762	Allocating memory within a 64K boundary I need to allocate a chunk of memory that doesn't cross a 64K boundary, so that I can access it all with the same half of the address, so that I can update pointers within a copper list without worrying about them being half read when I do it. Is there a smarter way to do this than by allocating 128K of memory and then just using part of it? Can I return the bits that I don't want to use?

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30 October 2019, 10:53	#2
Samurai_Crow Total Chaos forever! Join Date: Aug 2007 Location: Waterville, MN, USA Age: 49 Posts: 2,187	AROS has a way in its version but AmigaOS' Kickstart doesn't.

30 October 2019, 10:56	#3
DanScott Lemon. / Core Design Join Date: Mar 2016 Location: Tier 5 Posts: 1,212	http://eab.abime.net/showthread.php?...t=64k+boundary

30 October 2019, 11:57	#5
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,476	In my examples, in fact, as you may have noticed, I have always taken for granted an allocation of the kind Which one to choose between the two methods? If you are not concerned about memory restraints, allocate x+65536. If yes, the Alloc(x+65536), Forbid(), Free(), AllocAbs(), Permit() work well, but it fragment slightly the memory pool.

30 October 2019, 12:14	#6
meynaf son of 68k Join Date: Nov 2007 Location: Lyon / France Age: 51 Posts: 5,323	Doing FreeMem on partial block isn't recommended but in practice it works.

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