AOS scratch register question.

Thorham · 23 November 2012, 17:54

Hi,

I've read that when calling AOS functions, regs d0, d1, a0 and a1 are used as scratch registers by the AOS functions, and can therefore not be relied on. Is this correct?

Thorham · 23 November 2012, 19:13

Damn! I remeber now where I read it: IN THE FUCKING OS CODING MANUAL

How the hell did I forget this

mark_k · 25 November 2012, 20:17

Also note that there are some exceptions to the scratch registers, which are usually mentioned in the individual function autodocs. For example WaitBlit() in graphics.library is guaranteed not to modify any registers.

dalton · 19 December 2012, 08:10

The scratch registers are a Motorola standard, so it applies not only to amiga, but to almost any code compiled for 68k. Fp0 and fp1 are also scratch.

phx · 19 December 2012, 15:51

Except on Atari, where most TOS functions will also trash d2 and a2.

Mrs Beanbag · 19 December 2012, 19:34

so let me get this straight... all other registers are guaranteed to be preserved?
I did not know this.

Toni Wilen · 19 December 2012, 20:46

Every Amiga programming manual mentions it, it should have been impossible to miss it

Mrs Beanbag · 19 December 2012, 22:09

Amiga Machine Language by Stefan Dittrich (Abacus 1988) doesn't seem to... in fact in the examples everything seems wrapped in movem.l D0-D7/A0-A6,-(SP), oh well

Can't find it in Amiga System Programmer's Guide, either.

23 November 2012, 17:54	#1
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 47 Posts: 3,796	AOS scratch register question. Hi, I've read that when calling AOS functions, regs d0, d1, a0 and a1 are used as scratch registers by the AOS functions, and can therefore not be relied on. Is this correct?

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23 November 2012, 19:13	#2
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 47 Posts: 3,796	Damn! I remeber now where I read it: IN THE FUCKING OS CODING MANUAL How the hell did I forget this

25 November 2012, 20:17	#3
mark_k Registered User Join Date: Aug 2004 Location: Posts: 3,344	Also note that there are some exceptions to the scratch registers, which are usually mentioned in the individual function autodocs. For example WaitBlit() in graphics.library is guaranteed not to modify any registers.

19 December 2012, 08:10	#4
dalton tulou Join Date: Jun 2006 Location: Gothenburg / Sweden Posts: 88	The scratch registers are a Motorola standard, so it applies not only to amiga, but to almost any code compiled for 68k. Fp0 and fp1 are also scratch.

19 December 2012, 15:51	#5
phx Natteravn Join Date: Nov 2009 Location: Herford / Germany Posts: 2,510	Except on Atari, where most TOS functions will also trash d2 and a2.

19 December 2012, 19:34	#6
Mrs Beanbag Glastonbridge Software Join Date: Jan 2012 Location: Edinburgh/Scotland Posts: 2,243	so let me get this straight... all other registers are guaranteed to be preserved? I did not know this.

19 December 2012, 20:46	#7
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,534	Every Amiga programming manual mentions it, it should have been impossible to miss it

19 December 2012, 22:09	#8
Mrs Beanbag Glastonbridge Software Join Date: Jan 2012 Location: Edinburgh/Scotland Posts: 2,243	Amiga Machine Language by Stefan Dittrich (Abacus 1988) doesn't seem to... in fact in the examples everything seems wrapped in movem.l D0-D7/A0-A6,-(SP), oh well Can't find it in Amiga System Programmer's Guide, either.

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