Re: A89: Re: 89 timer


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Re: A89: Re: 89 timer




> 
> > What does a maskable on interrupt have to do with anything?
> > All that means is that the on interrupt will be called even if
> > interrupts are disabled.  To have a clock running all the time,
> > the processor would be turned on and off ~200 times a
> > second.  That's going to seriously effect battery life, and the
> > lithium battery alone can't run the processor.
> 
> No, you have it backwards.  I said MASKABLE interrupt, not
> non-maskable (sheesh, how could one get those confused :-).
> Anyway, the point I made with that is that the processor is
> ALREADY turned on and off 200 times a second whether the
> calculator is on or not.  Otherwise, it could not check for the
> ON key.
> 

Hmm... The ON key actually triggers an interrupt, as we all seem 
to agree on.  This means that the processor doesn't need to 
actively check for it.  After getting a HALT command, the processor 
goes into hibernation until it gets an interrupt. (the display has 
nothing to do with that process, but for long term HALTs, the 
screen is shut down by the preceding code... another totally 
unrelated matter, sorry...)  The approximately 200Hz interrupt that 
is normally running gets masked out (or maybe just plain turned 
off, I can't remember... its been a while) when the calculator is 
"turned off" so that the only thing to wake the processor back up is 
the ON key interrupt.  There is no 200 times a second scan for the 
ON key or anything.  The processor is effectively off, drawing very 
little current until that ON key is pressed.  A realtime clock, on the 
other hand, would require that the ~200 Hz interrupt be left on or 
unmasked, in which case the processor _would_ be powered up 
and down 200 times a second.  Of course, that interrupt is so 
dependent on battery voltage that a clock isn't really practical 
anyway, so its not a problem. :-)

Disclaimer: I don't know anything about the TI-89's hardware, nor 
much about the TI-92/92 Plus's hardware, so parts of this rant may 
not be accurate.  But I do know that TI is not stupid enough to have 
their calculator's prcessor activating itself continually when it is 
supposed to be off.

--
IMHO,
Ben Shakal
ben@sixg.com
neb@uclink4.berkeley.edu

"Linux: Because reboots are for upgrades."


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