Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-09, 08:42

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by Jepael

in PC Emulation

in PC Emulation

Two first FAT table entries are reserved and not used as FAT entries. One of the reserved entries contains a "media descriptor byte" or something equivalent and this byte can be used to detect what kind/size flppy there is so it can set the correct parameters to BIOS and actually use the rest of the …

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Re: Can anybody help me debugging the MS-DOS 3.3 boot sector?

Posted on 2015-03-04, 19:36

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by Jepael

in PC Emulation

in PC Emulation

Head: 1, Track: 0, Sector: 2, which is translated into sector #1441 in the image file. No, you have the math wrong, track 0, head 1, sector 2 is sector #19, not #1441. A 1.44MB floppy has 2880 sectors in total, 2 heads and 80 tracks, so that gives 18 sectors per track. On a given track, you read 18 …

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Re: Asus P5A wierd boot issue

Posted on 2015-03-03, 21:50

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Some boards have BIOS setting what should it do after power outage, you might want to check that. Also if the CMOS battery is running low, and when 5V standby voltage fades away, battery might not keep the chipset RTC clock ticking even if it preserves settings. When there is no clock in the chipset …

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Re: Newly made Gravis Ultrasound compatible cards ... what's the degree of interest?

Posted on 2015-03-01, 19:01

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Just an idea (again), if many people want a bit different things and it might be difficult to get the chips originally used in GUS (or other sound cards), why not make a FPGA board with enough sound card features like MIDI, joystick and audio connectors, onboard DRAM memory etc, and then design the …

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Re: Schneider 80286 PSU?

Posted on 2015-02-17, 15:18

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Some ancient PSUs just don't start if there is no load. So it might be OK after all. If you need to test it use a dummy load. I had to put 2 HDDs on one AT PSU before it gave any sane voltages out.

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Re: Reversing the Disney Sound Source

Posted on 2015-02-11, 23:36

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Congratulations, great stuff, good to know it works! I always considered doing DSS emulation with a modern MCU or even CPLD or FPGA, but I never bothered to think off-the-shelf TTL logic FIFOs could do the trick.

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Re: Reversing the Disney Sound Source

Posted on 2015-02-07, 20:01

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

So the parallel port pin is low only if both FIFOs have room, and if either FIFO goes full (output low), it turns off either transistor, and this lets parallel port pin high. Sounds reasonable and can easily be prototyped if the indication is wanted from only one FIFO. One final note, each IC should …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-05, 15:53

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Can you also post schematics (with componen values too) if you want to have a review? I just want to see how the FULL signal handling is now. If one of them is full, the other one should also be full, or they are one or more samples out of sync and this is terrible anyway. Therefore I think it is …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-03, 16:57

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Start with 4.7 kohm, but anything between 1k and 10k should work without hassle. 1M can be too weak. As long as it is there, you can change/tweak later.

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Re: Innovation SSI 2001 re-engineering and/or conclusions

Posted on 2015-02-02, 19:55

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

It seems the SN76489 chip uses only one IO address, so basically it only interferes with the second DMA controller at address C0h. Consider that C0h is the port for DMA channel 4 memory address, and DMA channel 4 is never used as it is the cascade channel (8-bit channels 0-3 of the first chip goes …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-02, 09:26

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Just to be sure, you measure points A+B for this variable resistor, right? Is that resistor value super important so a really exact value is needed? and yes, these are my pics (quick ones too!) and you can upload/use them to your heart's desire :) Thanks for the pictures! Yes, A+B is the total …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-02, 08:54

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

Allright, I measured R12. I am getting 174K between points A+B 80K between A+C 104K betwwen B+C is this helpful? Somewhat, thank you. Basically it is still connected to other circuitry which will affect the reading, so you are not just measuring the R12, and depending on what kind of circuitry it …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-02, 08:46

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

What's the type of the 4-bit FIFO chips? 74ALS232 (16x 4Bit) Thanks. Should work. If there exists a "HC" version, it will have more symmetrical output drive for the R2R dac, but I would not worry (the original LPT port had "LS" types as well). And, there is no series resistor between FULL output …

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Re: Reversing the Disney Sound Source

Posted on 2015-02-01, 19:44

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

What's the type of the 4-bit FIFO chips? The two FULL output pins should not be tied together, only one push-pull output should drive the transistor. And, there is no series resistor between FULL output pin and transistor base, it needs one or it might blow up something. I don't see how the samples …

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Re: AdLib to MIDI?

Posted on 2015-01-31, 11:39

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by Jepael

in PC Emulation

in PC Emulation

There is a tool to convert .DRO files to .MID files, so basically you can run a game in DosBox that plays Adlib music, capture the played data to .DRO file and convert to .MID file. Is this what you are trying to do? I don't know how well it will work, but at least it should be possible.

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Re: Covox Sound Master Reverse Engineering / Replica

Posted on 2015-01-30, 08:44

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by Jepael

in Marvin \ Sound

in Marvin \ Sound

I have heard that X-Ray can be used to detect the hidden traces. Not sure though if X-Ray is harmful to electronic components. If it was harmful, we would have broken laptops and cell phones after airport security. X-ray is also used for inspecting bad solder joints under chips. I know it is …

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Re: ISA Graphics Card Display Distortion

Posted on 2015-01-29, 19:07

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

If there is no flickering, so the pixels just are wrong color, my guess is that it is a palette issue (game might wite palette data too fast for the card to handle it). So I also suggest increasing 8-bit IO recovery cycles in the motherboard BIOS settings. It does not hurt to max out both 8-bit and …

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Re: Maybe a dumb question but...

Posted on 2015-01-27, 21:48

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'd say it depends how good the emulator is of course :) Most likely the emulator takes few shortcuts here and there to save CPU horsepower to emulate the rest of the system, so it may not implement all the details. The way how GUS interpolates samples sounds really awesome (at least it did in 1994 …

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Re: Maybe a dumb question but...

Posted on 2015-01-27, 20:44

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

No, you really need a special chip called serial audio transmitter. It is a chip that takes in the 16-bit PCM data from the serial audio bus (WS, BCK, DATA) and encodes the data into SPDIF format. You can then connect the SPDIF output to TOSLINK optical transmitter module or RCA connector. For …

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Re: Maybe a dumb question but...

Posted on 2015-01-27, 17:43

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by Jepael

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Should be possible. The DAC format looks pretty standard that should work with most SPDIF transmitters that are configurable. It is not I2S audio bus that would be the most compatible. I have some GUSes packed away in a box, I could take a look at some point if I find them.

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