ECS Denise.. is it worth it ?

[AmigaHope]

Actually DblPAL and DblNTSC *DO* work in ECS.

ECS had two major changes, one of which was the improved blitter (could blit more in one instruction, although the time to blit wasn't much improved since it was still memory bandwidth limited).

The other big change was programmable scanrates. Vertical refresh and horizontal refresh could now be set to arbitrary values within the supported ranges. To support this, higher pixel clock settings were made available, with the limitation that the faster pixel clock modes could only have 2 bitplanes.

Every AGA graphics mode works fine on ECS, as ECS supports exactly the same scanrates as AGA. It's just to do DBLPal/DBLNTSC/etc. you have to set the pixel clock to its highest speed, which limites you to 2 bitplanes/4 colors.

Note that it's actually possible to use a lower pixel clock on a high scanrate screen! For instance you could do DBLPal scanrates, but halve the pixel clock, and have a 320x512 screen in 16 colors on ECS.

[AmigaHope]

OCS Denise had half-brite mode, except for the revisions in the earliest shipments of A1000s (I forget the rev # that added EHB). I believe that you can still open EHB modes on the  original Denise, but you won't actually get the half-brite effect.

The high pixel clock (35ns) modes on ECS Denise weren't any slower than 16-color hires modes on OCS/ECS, because they limited you to 2 bitplanes instead of 4, thus keeping the bandwidth the same. ECS didn't actually add any faster fetch modes to OCS, so the bandwidth limitation remained.

AGA added faster fetch modes, which is why you can have 8 bitplanes at all pixel clocks.

[AmigaHope]

@Aminicle

ECS Denise is 100% compatible with software and screenmodes designed for OCS, you wouldn't actually need to have both an OCS Denise and ECS Denise on a switchboard like the Kickstart switchboards.

Just open your Workbench and stuff in high scanrate modes. When you start up your old games, they'll open up 15Khz screens just like normal (though you might need to change monitors or add a monitor switch).

[AmigaHope]

@LoadWB

EHB == "Extra HalfBrite". When I say "half-brite" I'm talking about EHB. They're the same thing.

And like I said, EHB is in EVERY Denise, from OCS to ECS, and in AGA Lisa. The only exception is in the *VERY FIRST* revision of OCS Denise in some A1000s shipped in 1985.

EHB was added to Denise not long after, so lots of A1000s support EHB. If you have one of the very early Denise revisions in your A1000 that do not support EHB, you can swap it out for a later OCS revision Denise that supports it.

You might even be able to put an ECS Denise in an A1000, but I don't know if you would be able to do much with it as you can't fit an ECS Fat Agnus in the A1000. (A1000s use the original "thin" Agnus which comes in a DIP package rather than PLCC. ECS Agnus was only ever released in PLCC Fat Agnus form, so there is no upgrade possible.)

I think it *might* be possible to enable the ECS Denise 35ns  pixel clock and variable horizontal scanrate without having an ECS Agnus, but since Agnus controls the DMA clock (and thus the vertical sync) you would be limited to the same vertical refresh rates, and line doubling might not work. My guess is that AmigaOS would refuse to let you try it anyway and you'd have to resort to hardware banging to enable any sort of ECS screenmode.

[AmigaHope]

@Piru

Piru wrote:
Yeah. 16 colour hires is painfully slow, too :-D

Well, it's SOMEWHAT faster than 16-color hires, actually. The DMA bus contention is exactly the same as 16-color hires, but for a given graphical operation the CPU is writing only half as much data.

Basically the speed is exactly same as opening a 16-color hires screen but only writing to 2 of the 4 bitplanes.

So in interactive GUI use a 4-color Productivity/DblPAL screen feels about as fast as an 8-color 15Khz Hires screen, or 33% slower than the equivalent 4-color 15Khz Hires screen. (Double Denise DMA traffic but Blitter DMA and PIO traffic stays the same at same color depth).

Edit: This is an oversimplification, I should point out. In OCS/ECS the CPU gets the same amount of bandwidth to chipmem  no matter what. CPU writes to chip memory on a 2-bitplane screen will always go twice as fast as a 4-bitplane screen provided there is no blitter activity. The blitter, however, gets extra bandwidth from unused Denise DMA cycles, so things like moving a window and text rendering, as well as other typical blitter-accelerated GUI operations, will go faster when you have less Denise DMA traffic.

Generally though I think for the way most GUI operations "feel", the (ECS) 4-color 35ns DblPAL 640x512 == 8-color 70ns PAL Hires 640x512 is a good comparison, but if you use a patch to replace blitter functions with CPU block moves, then all the 4-color modes will actually feel exactly the same (although theoretically you're wasting the few DMA cycles that the blitter could be using that the CPU can't get at).

[AmigaHope]

@Zac67

I think you could MAYBE coax a DblPAL-type mode out of an OCS Agnus/ECS Denise system... You'd set the pixel clock for 35ns pixels and double the horizontal refresh (I think Denise could force a horizontal blank without Agnus knowing about it)... and you'd keep the vertical blank the same. I really have no idea if Agnus has to cooperate with Denise on horizontal blanks (though I think you can free DMA time on the horiz. blanks so I guess there must be a capacity for Agnus to know about them). I really don't know enough about the internals to say for sure.

Denise at its maximum doesn't eat up much in the way of the CPU's allocated chip mem bandwidth, but at that point any *OTHER* DMA you do (particularly with the blitter) starts seriously hogging the bus away from the CPU.  By itself a 640x512x2bppx50Hz DblPAL screenmode eats just shy of 4 megabytes/sec of bandwidth. A1000/A500/A2000 chipset has roughly 3.5Mbytes/sec bandwidth dedicated to the chipset, and another 3.5Mbytes/sec that the CPU can use. You're not really stealing that much.

Once you start blitting stuff around a lot though, it eats up even more bandwidth and slows the graphics system down to a crawl (and basically kills the CPU if you have no FAST RAM). This is why CPUBlit-type patches speed up the system so much on high-bandwidth screens.

This goes double for A3000 ECS systems and AGA systems that give the CPU 32-bit paths to chip mem. Once you've eaten up the dedicated custom chip bandwidth, the blitter becomes a drag on the system rather than a benefit, as long as you have CPU cycles to spare.

Anyway the ECS 2-bitplane 35ns modes aren't so bad performance-wise, provided you have real fastmem and don't try to use the blitter. On the A3000 with its 32-bit chipmem  they're actually VERY nice if you don't like the fringing motion effects that you get on deinterlaced screens.

[AmigaHope]

@Nostalgiac

Well it's not going to help at all with games. Having full ECS will mean you can tweak your existing screenmodes though so that your flickerfixer can output modes that your monitor can handle, plus let you use 4-color ~31Khz modes directly.

Once you get the Super Denise installed, you should edit your screenmodes (stored in the Monitor files) so that your regular  screenmodes wind up at frequencies that your monitor can support. i.e. tweak your 15Khz modes so that your scandoubler/flickerfixer generates useable doublescanned modes. You are probably going to want to use more than the 4 colors that the native 31Khz ECS modes can do. XD

And again, this will not do diddlysquat for games. For that stuff you just need to get a better monitor that can handle a doublescanned PAL screenmode. =p