VGA Only monitor driver
 

Hi,

Just out of interest, what does VGA only actually do? I realise it isn't a monitor driver in it's own right and it seem to make the multisync driver look a lot better on my CRT but I'm now sure how it works or what it does.

I think it cranks up the frequency a little to increase compatibilty with VGA screens

Is it safe to use with all other drivers (eg HighGFX)?

After some more reading and rumors can I ask if using the 'VGA Only' driver increases the speed of the whole chipset or just the Lisa chip? I've been reading that it also increases the speed of AHI, how is that possible?

VGAOnly is not a monitor driver. It is a patch which *slightly* changes the other drivers. It applies only to those drivers which already are VGA compatible (DblPAL, DblNTSC, Multiscan). Those drivers switch DMA into double speed. For audio (not only AHI) this means that samples can be played back at 56 kHz rather than 28kHz as with normal PAL or NTSC modes.

Thanks Thomas.

So if it does switch DMA to double speed which as you say can increase the speed of other samples is it a good idea to always use it? Any side-effects or drawbacks from using it?

Thanks,
Chris

There is no "double speed" mode. DMA is still as fast (or slow) as previously.

Audio supports higher sample rates only because doublescan modes have halved horizontal scanline time (instead of standard 227 DMA slots, there is only about 120 slots or so, depends on mode) and all DMA in Amiga (except copper and blitter) is synced to scanlines, audio for example is 2 8-bit samples per channel per scanline. (same sample pair is repeated if rate is larger than DMA handle)

Hi Toni,

So if your running in a doublescan mode (eg DBLPAL) you get no additional 'benefit' from also sticking the 'VGA Only' monitor driver in your DEVS/Monitors folder?

Which ones are the doublescan modes? What about something like HighGFX?

I had left it in inadvertedly and was having weird screen issues with DpaintIII and Sysinfo on my 1200 equipped with Indivision... Removed it and all was normal again...

The screens in both apps were shifted to the right...