Re: A89: timings and osc


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Re: A89: timings and osc




On Sat, May 27, 2000 at 20:04:24 -0400, Scott Noveck wrote:
> 
> So if I go into TEX and set it for 200 seconds, I should get approximately
> 5 minutes?

Yes.

> So the screen refresh is a bit slower and the APD is at a different rate.
> Does this make any other difference?  Does it affect the auto-int 5 timing?

It affects everything that is based on this oscillator:

	autoint 1:	osc/2048
	autoint 3:	osc/524288  (when enabled)
	autoint 5:	osc/(X*Y)  (X=512 and Y=79 (HW1) by default)

	LCD refresh:	osc/X per line  (X=64 by default)
			i.e. osc/(X*Y) per frame  (X=64 and Y=128 by default)

Autoint 1 is responsible for scanning the keyboard, key debouncing and key
autorepeat. However, the speed of this interrupt cannot be changed and will
always run at the speed that the OS expects.

Autoint 3 does nothing useful. It's even disabled in hardware by default.

Autoint 5 is responsible for updating the software timers. This affects the
APD, cursor flash, link timeout, battery level checker and the waitstates-
according-to-battery-level update. The ROM initializes the hardware to
generate autoint 5 at 20 Hz. Programming a HW2 calc with HW1 values sets it
to 13 Hz, effectively resulting in longer APD and a terrible slow cursor
flash rate.

It also affects games that use the timer to generate proper delays. These
games will run 50% slower on HW2 calcs.


/Johan



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