Recommended settings for bog-standard i286

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TheMechanist
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Recommended settings for bog-standard i286

Postby TheMechanist » Thu 20 Jul, 2017 9:08 pm

Hi,
for testing purposes I'm running pcem with DOS on Ami i286 clone .. But I'm not sure which settings are best to get an emulation that is nearest to a real bog standard i286 (mass market & sold in europe) ...

My setup is atm

Ami 286/16 Mhz clone with OAK OTI067 Gfx (alternative Ati VGA Wonder 16 / Edge 16), 1 MB Ram, 40 MB Hdd, Adlib / SB 1.0

But what is the right "video speed" setting ? I read, that i286 had ISA-Bus with 16 Bit at 8 Mhz ..

Btw. will there be any difference in emulation speed when choosing different graphic cards ?

Thx
SarahWalker
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Re: Recommended settings for bog-standard i286

Postby SarahWalker » Thu 20 Jul, 2017 9:16 pm

OAK will probably be Slow 16-bit.

There won't be any difference between the emulated cards, hence the video speed selection.
teppic
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Re: Recommended settings for bog-standard i286

Postby teppic » Thu 20 Jul, 2017 10:17 pm

The XT (original PC) line had 8 bit expansion slots, the AT (286 lines) had 16bit, which are backwardly compatible with 8bit. 386SX systems also had 16bit because everybody still used 16bit expansion cards when the CPU was released.

I wondered about the video speed settings myself - I just select whatever the card type was.
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TheMechanist
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Re: Recommended settings for bog-standard i286

Postby TheMechanist » Sun 23 Jul, 2017 9:29 am

only because of interest .. and what do the video settings internally ? what happens if you choose 8bit or slow 16bit ? Is it linked to cpu clock, approximated data transfer rates or more a rule of thumb ?

Is it right that this speed is the speed for transfer between CPU and GfX card ?

How does - at least in real life - the gfx card (ram) speed matter, why is a et4000 faster than a oti ?
SarahWalker
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Re: Recommended settings for bog-standard i286

Postby SarahWalker » Sun 23 Jul, 2017 11:41 am

The video speed setting controls the number of waitstates added when the CPU accesses video memory.

Basically, when accessing video memory, the bus sets a minimum access time - for ISA this is 3 cycles at 8 MHz, VLB and PCI are quite a bit faster. Following this it depends on how quickly the graphics card can respond. This depends on several factors - how fast the memory is, whether video memory is already being accessed to draw the screen, and whether the card is doing anything clever to speed things up. For example, the ET4000 is known to have a very large write buffer, allowing multiple CPU writes to be queued up internally and then processed when video memory is available. Cards that use VRAM instead of DRAM eliminate memory contention when drawing the screen (by having that occur on a separate bus), which speeds things up further.

If the card has a narrower bus than the CPU (eg an 8-bit card on a 16-bit bus) then accesses above that size will be split into multiple transactions, slowing things down further.
ecksemmess
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Re: Recommended settings for bog-standard i286

Postby ecksemmess » Tue 25 Jul, 2017 7:07 am

Something I've always wondered about: why is the video speed user-selectable? Won't there always be a single most sensible value for that setting for any given board choice and machine configuration? As such, wouldn't it make more sense for PCem to simply work out which video speed setting is appropriate for the given configuration, rather than leaving it up to the user? I'm struggling to think of a scenario in which granting the user free selection of the video speed would benefit accuracy--quite the contrary, really, as it's a setting most users are bound to find rather opaque. I guess some of the emulated boards existed in both ISA and VLB variants, so the video speed setting might currently be the only way for the user to select which of the two variants they'd like, but surely that's an occasion where it would be more intuitive to simply represent each variant explicitly in the video selector as a separate board (or offer a "configure" button as is done with the VRAM settings, I suppose...)? All in all, it does seem like it would make sense to move toward having PCem figure out the most appropriate video speed setting on its own, preferably in a sophisticated process that takes into account all of the various performance-affecting parameters and considerations described in the above post.
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omarsis81
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Re: Recommended settings for bog-standard i286

Postby omarsis81 » Tue 25 Jul, 2017 4:04 pm

ecksemmess wrote:Something I've always wondered about: why is the video speed user-selectable? Won't there always be a single most sensible value for that setting for any given board choice and machine configuration? As such, wouldn't it make more sense for PCem to simply work out which video speed setting is appropriate for the given configuration, rather than leaving it up to the user? I'm struggling to think of a scenario in which granting the user free selection of the video speed would benefit accuracy--quite the contrary, really, as it's a setting most users are bound to find rather opaque. I guess some of the emulated boards existed in both ISA and VLB variants, so the video speed setting might currently be the only way for the user to select which of the two variants they'd like, but surely that's an occasion where it would be more intuitive to simply represent each variant explicitly in the video selector as a separate board (or offer a "configure" button as is done with the VRAM settings, I suppose...)? All in all, it does seem like it would make sense to move toward having PCem figure out the most appropriate video speed setting on its own, preferably in a sophisticated process that takes into account all of the various performance-affecting parameters and considerations described in the above post.

I always have the same though as you do.
Most cards are one bus only, for instance why have the possibly of having the Trident 8900 to be a high end PCI card? That's nuts
For me, and to have PCem as historical as possible, each card should be locked to its native bus (and preferably speed).
Also, selecting a 286 board and plug a PCI card would be totally illogical. I wonder how it even boots
SarahWalker
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Re: Recommended settings for bog-standard i286

Postby SarahWalker » Tue 25 Jul, 2017 5:17 pm

It's user selectable because a) I haven't actually benchmarked each card in reality, partly because I don't own all of them and partly because speed will generally vary depending on what video mode is in use, and b) because it can sometimes be interesting to modify in real time to see the effect on system performance. I should probably add a 'Card Default' option, similar to the waitstate controls, with a VERY rough estimate of performance, but I haven't done that yet.

The video speed selection does not control bus type, saying it has the speed of a high end PCI card does not make it a PCI card! Generally cards that support PCI will act as PCI on a PCI-supporting system, otherwise they will be ISA/VLB (from a system perspective there's little difference between the two).
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omarsis81
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Re: Recommended settings for bog-standard i286

Postby omarsis81 » Tue 25 Jul, 2017 10:08 pm

I like that idea of each card having a default setting.
I have a couple of the cards currently emulated. I can help with the benchmarking.
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leilei
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Re: Recommended settings for bog-standard i286

Postby leilei » Wed 26 Jul, 2017 12:53 am

For more accurate speed variance, there's some real slow ISA16 SVGA junker cards out there not on the emulated list, Realtek made some of them. (the appeal was low cost and very low size for '94)

Off the top of my head for an appropriate benchmark I can't think of any for raw video performance w/o cpu influence. Of the exact cards on the list I currently have available in easy reach are a few different Phoenix Trio64s and the Stealth 3D 2000 (which I'm paranoid of using in fast systems).
ecksemmess
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Re: Recommended settings for bog-standard i286

Postby ecksemmess » Wed 26 Jul, 2017 2:48 am

SarahWalker wrote:I should probably add a 'Card Default' option, similar to the waitstate controls, with a VERY rough estimate of performance, but I haven't done that yet.


Yeah, this is kind of what I was getting at. I'm very much in favor of this.
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TheMechanist
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Re: Recommended settings for bog-standard i286

Postby TheMechanist » Thu 27 Jul, 2017 12:07 pm

@Sarah - thx for your explanation !

I tested PCem settings with some dos bechmarks - Checkit 3.0, Landmark 6.0 & topbench .. very close to real machines, very impressive piece of code !

Compare here:

http://mastodonpc.tripod.com/bench/speed.html

Unfortunately some machine specs - especially type of graphics adapters - are not detectable ..

btw. It seems to be a good choice to collect that kind of real machine bechmarks ..
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omarsis81
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Re: Recommended settings for bog-standard i286

Postby omarsis81 » Thu 27 Jul, 2017 12:44 pm

TheMechanist wrote:http://mastodonpc.tripod.com/bench/speed.html

Is that site yours? Nice, but I don't see the TOPBENCH results, I think it is the most reliable of them all
What other utility is useful for benchmarking 2D video cards? "Final Reality" has a 2D tab and measures speed and bandwith, any good?
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TheMechanist
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Re: Recommended settings for bog-standard i286

Postby TheMechanist » Thu 27 Jul, 2017 2:27 pm

no, not my site, the benchmarks are from 2001 .. but it's hard today to benchmark real hardware since most of it is retired & was thrown in the trash .. checkit is a very accurate benchmark too .. and landmark was the defacto standard at that time ..
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omarsis81
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Re: Recommended settings for bog-standard i286

Postby omarsis81 » Thu 27 Jul, 2017 2:38 pm

TheMechanist wrote:no, not my site, the benchmarks are from 2001 .. but it's hard today to benchmark real hardware since most of it is retired & was thrown in the trash .. checkit is a very accurate benchmark too .. and landmark was the defacto standard at that time ..


According to the TOPBENCH's developer, he wrote his own benchmark tool because none of those utilities were reliable enough
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TheMechanist
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Re: Recommended settings for bog-standard i286

Postby TheMechanist » Thu 27 Jul, 2017 3:13 pm

can't proof it, maybe, but it's definitately helpful to have more than one benchmark and values that run on real hardware ..

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