Re: CGA intensity

Posted on 2022-05-16, 16:00

by

by reenigne

in Marvin \ Video

in Marvin \ Video

Not on a standard CGA RGBI monitor, no. There are some sRGB colours that are just outside the CGA RGBI gamut, even with dithering. This wasn't fixed until we had EGA monitors (with the 350-line mode) and VGA monitors.

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Re: CGA intensity

Posted on 2022-05-16, 07:03

by

by reenigne

in Marvin \ Video

in Marvin \ Video

Mix of red and white. Switching on the intensity bit increases the output to the red, green and blue electron guns. For red, the non-intense version is usually #aa0000 and the intense version #ff5555.

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Re: PC1512 graphics

Posted on 2022-03-17, 08:12

by

by reenigne

in DOSBox Games/Apps

in DOSBox Games/Apps

Reply on a previous thread listing some games with PC1512-specific graphics: Re: Trying to add Amstrad PC1512 special video mode.

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Re: So just how does DMA on a 8088 based PC work?

Posted on 2021-12-03, 21:24

by

by reenigne

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

From the point of view of the CPU, an IO cycle (memory or port) can be split into two parts by a DMA - it looks like wait states are inserted are inserted between T3 and T4. From the point of view of the IO device, IO cycles are not split.

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Re: So just how does DMA on a 8088 based PC work?

Posted on 2021-12-02, 09:08

by

by reenigne

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Not waveforms exactly, but similar... attached are some logs from my ISA bus sniffer showing the exact timings of some DMA cycles and how they interact with CPU bus accesses. There's some more information about interpreting these logs at https://www.vcfed.org/forum/forum/genres/pcs-and-clones/32469- …

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Re: Art of CGA

Posted on 2021-08-19, 13:04

by

by reenigne

in Marvin \ Video

in Marvin \ Video

I came across these today - they definitely belong here: https://twitter.com/pinot/status/1426567442466226178 and https://twitter.com/pinot/status/1427678504053792779

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Re: Art of CGA

Posted on 2021-08-11, 18:23

by

by reenigne

in Marvin \ Video

in Marvin \ Video

That's excellent work. What program(s) did you use to create it? Sorry about the late reply, I just saw your message. I use photoshop, but there is a lot of manual editing and pasting going on so it's not exactly a automated process. Here is another 320x200 4 color image. https://i.imgur.com/ …

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Re: VGA difference of blacks?

Posted on 2021-04-02, 16:35

by

by reenigne

in PC Emulation

in PC Emulation

Looking at some RAMDAC datasheets I don't see anything that would indicate a difference between blanking level and RGB(0,0,0) level. VGA/SVGA (unlike CGA) isn't based on TV formats and uses separate sync lines so there isn't any need for separate blank and black levels on the VGA cable. Some …

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Re: Amstrad PC 1512

Posted on 2020-10-25, 11:57

by

by reenigne

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Errius wrote on 2020-10-25, 11:40: Does Moonbugs run on it? I believe so. Though I haven't actually tried it - I no longer had the PC1512 when I learn of that game's existence.

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Re: Amstrad PC 1512

Posted on 2020-10-25, 11:55

by

by reenigne

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

(I was never able to complete Bruce Lee because of this) I did, despite not knowing what I was looking at half the time because of the seemingly-designed-for-composite-only graphics. That's weird - the version that I played (with actually came bundled with the Amstrad PC1512) had both composite and …

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Re: Amstrad PC 1512

Posted on 2020-10-25, 07:15

by

by reenigne

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I only ever ran across one CGA game that wouldn't run at all on the PC1512 (Astro Dodge, which modifies CRTC registers in a way that the PC1512's CGA implementation doesn't support). The additional speed did make some games more challenging (I was never able to complete Bruce Lee because of this). …

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Re: MCGA monitor at 15 KHz?

Posted on 2020-10-16, 22:07

by

by reenigne

in Marvin \ Video

in Marvin \ Video

It'd definitely be an interesting exercise to see what registers are programmed to what values in various modes by the MCGA BIOS and to see what happens if you mix and match register values from different modes.

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Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-09-26, 15:18

by

by reenigne

in PC Emulation

in PC Emulation

However, bear in mind that the 8088MPH speed test was never meant to be an emulator torture test - it was just sufficiently sensitive to tell IBM PC/XTs from contemporary machines with similar (but not identical) timings. Getting the speed test to pass doesn't mean that all instructions are correct …

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Re: Sound high-pass filter vs peaks?

Posted on 2020-09-17, 13:46

by

by reenigne

in PC Emulation

in PC Emulation

What happens then if you supply a 5V voltage(e.g. only +32767) values to SDL? That can happen if some app hangs while sampling for some reason(e.g. sound blaster not receiving interrupt ACK anymore with the last sample being 255 in 8-bit mode or 65535(both unsigned samples))? Won't that possibly …

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Re: Sound high-pass filter vs peaks?

Posted on 2020-09-17, 08:40

by

by reenigne

in PC Emulation

in PC Emulation

It depends on a lot of details of your filter implementation - and isn't necessarily an easy calculation. But why do you actually need a high-pass filter in the first place? Lower frequencies aren't going to be audible either way - the speaker/air/ear system filters them out regardless just as it …

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Re: Art of CGA

Posted on 2020-08-13, 12:53

by

by reenigne

in Marvin \ Video

in Marvin \ Video

I would love to download all these pictures and display them on my Original IBM 5150 with the CGA Colour Monitor. Is there a package to download? Are there any dos/8088 viewers that can display these images? I have a program ( https://www.reenigne.org/misc/cgadview.zip ) which can display most . …

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Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-06-05, 06:20

by

by reenigne

in PC Emulation

in PC Emulation

superfury wrote on 2020-06-04, 21:56: It makes me wonder, though... Can color burst even be disabled in text mode by clearing bit 2 of the CGA Mode Control register? Or does it have no effect in text mode? It has the same effect in text and graphics modes.

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Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-05-26, 17:45

by

by reenigne

in PC Emulation

in PC Emulation

superfury wrote on 2020-05-26, 16:36: Does the credits of 8088 MPH use a REP prefix? Not during execution of the actual effect. It does in the init code, but timings being off there shouldn't affect anything. There must be something else broken.

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Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-05-24, 22:00

by

by reenigne

in PC Emulation

in PC Emulation

Also, can you explain what happens during the first 2/3 cycles of that OUT instruction? As UniPCemu currently runs it, that weird case without the idle bus cycles will never happen. The first cycle ticks normally. Then, it waits for T1 and on that cycle executes two idle bus states, before starting …

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Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-05-24, 19:53

by

by reenigne

in PC Emulation

in PC Emulation

Just have been looking at xtce's code. What's the whole deal with the tFirstIdle and tSecondIdle cycles? Does it have something to do with this current UniPCemu idle bus cycle problem? I don't remember the exact details, but in the process of testing XTCE against XTServer+ISA bus sniffer, I must …

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