Re: Re: [stella] the B. Watson's problem...

Subject: Re: Re: [stella] the B. Watson's problem...
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Wed, 22 Aug 2001 21:32:56 +0200
> Uhm... so when using TIM1024T or TIM8T once per frame, I'd get a
> reliable frame counter for free?

No, that's not how it works. First of all the timer overflow should
be active for all timers, it's just a matter of the lowest bit in
the address to read it. Address $284 is INTIM and address $285 should
be the timer overflow. But since some of the address bits are ignored
when reading from the RIOT, reading from $294 (TIM1T) should be the
same as reading from $284 (INTIM) for example.

When a timer has reached $00 it stays at that for as long as the
timer is selected (64 cycles on TIM64T) and then wraps to $FF. The
timer then goes into TIM1T mode and keeps counting back. Everytime
the timer wraps from $00 to $FF the interrupt flag is set (if
timer interrups are enabled) and I think the timer overflow is
increased or decreased.

> Is the SEI at the beginning of most games unnecessary then?

Not really. The 6507 has no interrupt connections on the outside,
but the interrupt lines on the inside are still there. So theoretically
it might be possible that an interrupt signal could accidentally be
generated in the processor.

Ciao, Eckhard Stolberg

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