[Coco] CPU speed in MIPS
jcewy at swbell.net
Fri Apr 20 00:44:17 EDT 2007
William Astle wrote:
>> Diego Barizo wrote:
>>> Surprisingly, the high speed poke turns a sluggish CoCo into a PC
>>> killer (The T.1100 laptop)
>>> The poor rating on the Print test for the CoCo 3 is because I used one
>>> of the hi-res text modes.
>>> But anyway, the CoCo3 seems slower than a 2. Might be because the 3 is
>>> always in "all RAM"?
> That's actually easily explained. Between every statement, there is a
> poll for the BREAK key. On the original color basic, that meant doing a
> full poll of the keyboard between every statement. In newer versions,
> POLCAT was patched to check if any key was down and if none were down at
> all, it didn't bother polling the keyboard. The upshot of this is that
> BASIC runs faster as long as no keys or joystick buttons are pressed.
> Unfortunately, a patch in the CoCo3 removed the check in POLCAT so that
> the keyboard is scanned completely between every statement again. That
> means that the system runs a bit slower than an equivalent CoCo2.
> IIRC, there's also a replacement to the command interpretation loop in
> DECB 1.1 which does the same thing so you would think that DECB 1.1
> would solve the problem on the CoCo3. Unfortunately, the patching
> routine in the CoCo3 recognizes DECB 1.1 and patches that routine out
> too. Useful, eh?
> So, basically, the CoCo3 is running slower than the CoCo2 on plain basic
> statements because of the BREAK check process is scanning the keyboard
> whether a key is down or not.
I think I've seen a POKE (or series of POKES?) that purports to fix
this. I don't recall now where I found that.
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