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Re: VGA difference of blacks?

Posted on 2021-04-02, 16:35

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 …

Re: Amstrad PC 1512

Posted on 2020-10-25, 11:55

(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 …

Re: Amstrad PC 1512

Posted on 2020-10-25, 07:15

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). …

Re: MCGA monitor at 15 KHz?

Posted on 2020-10-16, 22:07

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.

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-09-26, 15:18

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 …

Re: Sound high-pass filter vs peaks?

Posted on 2020-09-17, 13:46

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 …

Re: Sound high-pass filter vs peaks?

Posted on 2020-09-17, 08:40

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 …

Re: Art of CGA

Posted on 2020-08-13, 12:53

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 . …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-05-24, 22:00

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 …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-05-24, 19:53

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 …

Re: 8088 MPH: We Break All Your Emulators

Posted on 2020-04-05, 10:38

First of all: Happy 5th anniversary to 8088MPH and everyone involved! Thank you! I hadn't realised the anniversary was this weekend. But let's get deeper into the technical details: IIRC the 1024 color mode outputs only the duplicated first scanline of every character row and does that by starting …

Re: Best CGA & Hercules games

Posted on 2020-03-21, 15:55

Technically this game has fantastic effects that I never saw on cga on any other game: https://www.youtube.com/watch?v=SygD93F95js What effects in particular are you thinking of? I didn't notice anything particularly technically interesting about the game, but I'm always on the lookout for new CGA …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-03-13, 17:22

What about just splitting the 8088 MPH speed test part into managable chunks for the bus sniffer(of course starting with a jump to get the correct start cache situation)? Like I said, that's the tricky bit. The queue and bus state also need to be in the right state for each instruction. If I can …

Re: 8088 MPH: We Break All Your Emulators

Posted on 2020-03-12, 14:08

Just found out something: CGA applies the memory write waitstates when updating the memory mode(changing mapped memory layout)? So when updating the memory with the new layout(due to changing VGA memory mapping it uses) it sets the waitstate for the current instruction(which it shouldn't)! Not sure …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-03-12, 13:55

Do you have some sniffer log of the metric cycle check done at the start of the demo(as well as it's starting address, perhaps the instruction jumping to it for the first time)? Unfortunately that's easier said than done - the ISA bus sniffer only has 2kB of RAM on the ATMega328 microcontroller …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-03-12, 12:12

OK. But those 1-cycle startup after the start of IN/OUT, 2-cycle for non-DX IN/OUT BIU idle following that and 1-cycle waitstate on all I/O bus operations is correct? 8088MPH reports 1547 metric cycles now. The PC/XT motherboard imposes a 1-cycle waitstate on all port IO instructions, yes. As for …

Re: UniPCemu cycle accurate 8088 implementation

Posted on 2020-03-12, 10:13

I've just been looking at https://github.com/reenigne/reenigne/blob/master/8088/8088.txt again. Pay no attention to that document - it's an older one and the timings there are just from the published ones if I recall correctly. https://github.com/reenigne/reenigne/blob/master/8088/xtce/xtce.h is …

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