🚀 go-pugleaf

In article <6493@tekig5.PEN.TEK.COM> brianr@tekig5.PEN.TEK.COM (Brian E
Rhodefer) writes:
>
> My copy of the Exec volume of the RKM, in the chapter on Interrupts
> (Ch 7, I believe), says that Interrupt Server routines can't count
> on the contents of A6, and that only regs D0-D1/A1/A5 are scratch.

To be precise, what the RKM says is that the registers d0,d1,a0,a1 are
scratch registers that are automatically saved by the kernel, and so are
registers a5 and a6, because they are often used by servers.

> a) if everyone indeed preserves A6, as the RKMs appear to mandate, then
>    they should be able to depend on the Kernel's loading of A6 with SysBase

The kernel pre-saves a6 for you so that *you* may load it with whatever you
want. The a6 register is indeterminate at the beginning.

> b) if nobody depends on A6, as the RKMs suggest, and the kernel
>    saves&restores it, then A6 can be regarded as scratch

Correct.

> Is the RKM inaccurate/incomplete here?  I don't have to push&pop A6
> in my Server routine, do I?

You don't have to, the kernel does it for you. Just don't make any assumptions
as to the contents of the a6 register when your interrupt server gets
started. (interrupt handlers have ExecBase in a6 though)

The new RKM are accurate and complete, but I suggest you also buy the "Guru's
Guide, Meditation #1 - Interrupts" by Carl Sassenrath, the creator of the
Exec.

>Brian Rhodefer

Valentin
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