[stella] RIOT Timer questions

Subject: [stella] RIOT Timer questions
From: "C. Bond" <cbond@xxxxxxxxxxxxx>
Date: Mon, 08 Sep 2003 15:19:23 -0700
I've searched the Stella archives for some specific details on the
operation of the timer which are unclear from the data sheet. Maybe
someone could help with these questions:

1) It appears that when the count expires (hits zero) its next value is
$FF and it switches to single-count-per-cycle mode (if it wasn't already
there). Apparently at that time an interrupt flag is set in a register
that appears to be addressable. Question: can this flag be polled to
determine count completion on the 2600? What memory address?

2) When the timer switches to single-count-per-cycle mode after count
completion, it begins decrementing, according to the data sheet, down
to -255. Question: Is -255 the same as 0? Question: does the counter
then stop at 0, or does it rollover and continue counting?

3) Some games appear to fail unless the timer is initialized to some
value prior to reset. Question: What is the default, initial state of
the timer -- or is it random?

Thanks for the help.


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