On Thu, 24 Feb 2005, William Chops Westfield wrote:

>> Depends. On bit fiddeling (for instance decoding a data stream in
>> software) the 8/16/32-bitness of a processor hardly matters. If this
>> were the case I the SX at 75 MHz would have been a good choice.
>> 
> Heh.  I recently discovered that accessing the IO space from one of those 
> nifty new 3+ GHz Intel processors is ENORMOUSLY expensive.  Close to a 
> microsecond (3000 instructions worth!), with possible additional overhead, 
> since it can't be executed out of order and does weird things to the pipeline 
> in attempts to keep the stuff internal and external properly synchronized... 
> You can sort of see that it HAS to be that
> way, but sheesh - the 8086 could access io ports in about a microsecond, too, 
> and something like a scenix...

I have uses x86 (pentium 2 and 3) machines to drive hardware directly, 
200nsec port read/write is achievable on the parallel port (pci mapped) 
and isa (16 bits).

Another option are PCI io cards which can be made to do raw io with a 
suitable driver. There is a general purpose PCI io chip that offers 64 
digital io lines and a few serial. I have not used it (yet).

Peter
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist