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Old 15 August 2012, 21:18   #38
mc6809e
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Join Date: Jan 2012
Location: USA
Posts: 293
Quote:
Originally Posted by Thorham View Post
Not saying that, I'm saying that peecee style VBL handling is uncool.


Does it take up so much time you'd use polling? That sucks

Maybe I'm missing the point
Autovectored interrupts on the 68000 have the annoying property that the 68000 must sync with an internally generated E-clock running at CLK/10 during interrupt handling. This can add up to 18 cycles on top of the time needed to push state onto the stack -- up to 44 cycles total.

And then you have to worry about the time it takes for the current instruction to complete before interrupt handling can even begin. A DIVU can delay interrupt handling by 100+cycles. This can be helped by executing a STOP and waiting for an interrupt, but the E-clock still complicates things. There are even situations where an interrupt handler must be padded with a variable number of instructions based on the predicted phase of the E-clock so as to perfectly time 68000 writes to chip registers. This might happen when reprogramming the sprite registers with a MOVEM in the middle of a scanline.

Polling is quick and simple.
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