APU x $4015 reads?

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APU x $4015 reads?
by Zepper on 2016-07-18 (#175630)

Let's take square wave 1 active-time-left (atl) set at $4003. It's decremented twice per frame.
On a lda $4015 and the atl goes 1->0 right before the effective $4015 read, does $4015 return 1 or 0?

Re: APU x $4015 reads?
by Disch on 2016-07-20 (#175831)

I'm not aware of any delay. So if the decrement happens before the read, you would read 0.

Re: APU x $4015 reads?
by Zepper on 2016-07-21 (#175902)

Disch wrote:

I'm not aware of any delay. So if the decrement happens before the read, you would read 0.

It bugs my mind. Actually, the order for running the units is PPU->APU->CPU. If I change it to CPU->PPU->APU, on $4015 reads, the atl=1, not zero as I'm doing. Got it?