I've found that it can depend on the assembler.  The assembler usually
     sets $ to the PC value of the current instruction, not to the value
     that would exist after the goto is executed; therefore goto $ would be
     the proper notation for an infinite loop.  goto $-1 would go to the
     previous instruction.  The assembler will take care of the fact that
     PC has changed by the time the goto executes.

     If fact, your examples are inconsistent on this matter.
     If " goto $-1" returns you to the current instruction, then goto $+1
     would send you two words downstream instead of to the next
     instruction.


______________________________ Reply Separator _________________________________
Subject: Re: Code error
Author:  Andy Kunz <montana@FAST.NET> at Internet
Date:    2/20/97 4:18 PM


>Isn't an infinite loop done with:   goto   $

No, because PC has been incremented to point to the next instruction.
Standard notation is to do it     goto $-1 for a 1-word wide instruction.
If you were using a Z-80, you could   JP $-3, since JP is a three-byte
instruction (0xC3, LSB, MSB).

Funny, but that's the way it is.

>In your example, if the statement previous was some other goto, it might not be
>infinite.  ie:    goto  $+2
>                  goto  $-1

Here's a hint.  If you have to a waste time, and you would normally write it as
        NOP
        NOP
        NOP
        NOP

try using the following instead.

        goto    $+1
        goto    $+1

Both take 4 instruction cycles, but you only need half as many instructions
to do it.

Warning - if you're using interrupts and need very close catching of the
interrupt, go with the NOPs instead.  The interrupt won't be serviced until
the current instruction is finished, which takes 2 times rather than 1 in
this case.

Andy
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