28 May
2014
28 May
'14
9:32 a.m.
On 05/28/2014 08:16 AM, Guy Sotomayor wrote:
If an instruction did an indirect memory reference and
the referenced
memory location had bit 15 set (which indicated further redirection) the
instruction won't complete until it fetches a word with bit 15 clear. A bug
where a word refers to itself (with bit 15 set) or back further in the chain
would result in an "infinite indirect loop". This was unbreakable since
interrupts are only processed at the completion of an instruction. A reset
was the only way to break out of it.
If memory serves, there were more than one or two old systems where
infinitely looped indirect addressing was possible.
Were there any where looped "Execute" instructions were possible?
--Chuck