On Wed, Jun 21, 2017 at 06:46:08PM +0100, smf wrote: > On 21/06/2017 18:29, firstname.lastname@example.org wrote: > > >... that I never used LP IRQs but thought that it would trigger only > >when the button line is grounded within a specific timing window so > >some kind of synchronisation with raster position would be required > >for the IRQ to happen. But that's a different subject anyway. > > A light pen is a simple sensor that triggers when a brighter than normal > light is detected. The VIC just latches the x & y position & fires an > IRQ when it is triggered, because it assumes that if the light pen can > see the gun then it must be over the current pixel. > > Adding something to VIC to ignore pulses outside the visible portion of > the display would be a waste of space. IIRC the LP stuff can be triggered only once per frame, this makes it a bit inconvenient to use for non-lightpen uses like we are discussing here. It would be nice if we could just read out the current X coor directly, but nope. Segher Message was sent through the cbm-hackers mailing listReceived on 2017-06-21 20:00:02
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