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Yes, I'm confident that I didn't really know what overflow was for the first half a year or so. Nowadays I am now entirely dependent upon unit tests: for the 6502 I apply those by Wolfgang Lorenz, those by Klaus Dormann, the AllSuiteA tests, the BCD-specific tests produced by hoglet right here on th...

no negative values. Have no idea if that really matters. Adding a DC offset, i.e. a component at zero frequency, isn't going to affect the acoustic spectrum or the subjective sound. But it may not be good for your loudspeaker, if it gets that far. You mean were the one program in charge of the enti...

It's a twenty-year old memory, I'm sure I'm in error. I was pretty sure that shift-left and OR was the culprit in E-Type's case, but clearly not, and if I had to guess about what led to my false Exile memory, possibly it's just getting the flags right? I'm pretty sure I had overflow wrong for a whil...

Using no science whatsoever, I played about with the filtering options I can apply in Clock Signal for free and subjectively thought that applying a 7kHz lowpass filter sounded most similar? Heavily subject to prejudices about nice round numbers, of course. It's attached.

Alas I discovered that I've broken loading of Way of the Exploding Fist at some point, so I've still got a distance to go. That one's interesting because it goes straight to the hardware rather than using the normal ROM routines for loading, unlike 99.99% of titles. So it tests both your tape hardwa...

I'll give both of those a spin in Clock Signal when I get a chance, to see whether it suffers the same audio fate. But for the record, specifics on this drift a little every now and again but right now it's: point sample the output audio at 500Khz and then apply a Kaiser Bessel filter to try as best...

Oh, I'm the original author of that tokeniser — it originates from ElectrEm. Apologies for the kooky types, they're the SDL names for what would eventually be standardised stdint.h, but the code predates C99 support in the compilers I had access to way back when. Apologies being made, I should proba...

If you promise not to look at any of the rest of the code, or at least not to judge me on it, you can also grab the FX-80 font directly from the ElectrEm code , where I recall retyping it by hand. Format is a 256-entry array of arrays, each letter being 11*9 ints: { // 77 M W, 0, 0, 0, 0, 0, 0, 0, W...

Why yes, I am making an OTF font based on a ROM dump from an old Amstrad DMP-2000 … Slight digression, but I had a quick look at what I did in ElectrEm a hundred trillion years ago, and when emulating an FX80-style printer it: embeds a Type 3 font directly into the PDF; in which it sets up a functi...

Re: Clock Signal, for macOS it is install and run. There are also quite a few things for which I referred to ElectrEm (especially ADC/SBC decimal logic, and tape interrupt logic), so there's a continuity there. And, sure, it's multisystem but only the one Acorn machine so file it as you will.

in Apple world it's exceedingly rare that a deprecated API has continued working indefinitely. Nowadays it's rare that they continue working for very long at all. Whilst this is true, I think it is dangerous to draw conclusions from what has happened before. One has to consider the impact on Apple'...

the removal of OpenGL from macOS in about a year. I've not seen elsewhere any confirmation that Apple plan to "remove" OpenGL. They've deprecated it, yes, but many 'deprecated' APIs keep working indefinitely to support old apps. If there has been an official statement that they plan to remove OpenG...

Except they're not that high on anything but an retina Mac. Even high res PC screens are just sub-retina and scaling leads to obvious loss of quality whether it is raggedness or, once that's been filtered out, looking fuzzy instead. Phones and tablets are also very high density (568dpi on the curre...

The B-em window starts off incredibly tiny though. Is there a way to enlarge it while maintaining the correct aspect ratio? I assume this is one of the "retina" screen Macs that has getting on for twice the resolution of a typical PC. Only if Allegro is going out of its way to force that upon you (...

The Apple II is the obvious predecessor: it's also sans proprietary chips, just about popular enough to be worth cloning, and a legal clone was eventually delivered. But that wasn't until 1984, reflecting the amount of interest the industry had in further propagating the Apple II. It's an open slot...

I think it is just simply that it was a published open standard, no lock in and no licensing. You wouldn’t get that from Nintendo for example. It wasn't a published open standard, it was just built in a hurry from off-the-shelf components. The BIOS was proprietary and copyrighted, and lawyers were ...

I think it is just simply that it was a published open standard, no lock in and no licensing. You wouldn’t get that from Nintendo for example. It wasn't a published open standard, it was just built in a hurry from off-the-shelf components. The BIOS was proprietary and copyrighted, and lawyers were ...

Another small release: ADF support was broken, specifically sectors would not all be transcribed to the disk surface. It was a failure properly to factor out the relevant logic when implementing support for the analogous MSX file format, so had probably been broken January. But now is no longer. I s...

The variant in the Master System and Game Gear has a 16-bit shift register rather than a 15-bit, but it's embedded into the VDP so it's not necessarily drawn from official blueprints.

Therefore the SN can definitely accept a very short write signal — 2.5 cycles @ 3.58Mhz. Definitely a lot shorter than 32 cycles, and prone to suggest that the SN can accept a new value within at most 1.25 of its own cycles. Schematics: The 74LS128 is slightly to left of centre at the bottom of her...

Has anyone successfully tried PWM on the Beeb? My understanding of the SN76489 is that it effectively updates at 4 MHz / 16 or 32, which would add severe quantisation to any PWM signal, limiting output quality. I had always assumed that volume changes take effect immediately, not being bound to the...

Has anyone successfully tried PWM on the Beeb? My understanding of the SN76489 is that it effectively updates at 4 MHz / 16 or 32, which would add severe quantisation to any PWM signal, limiting output quality. I had always assumed that volume changes take effect immediately, not being bound to the...

If the CPU constraint weren't in place then to throw out a third possibility: 1-bit pulse density modulation . The name is pretty descriptive: it's a lot like pulse width modulation except that instead of pulsing your 1-bit signal on and off for periods that correspond to the source data, you pick h...

The advantage in ElectrEm of having the video post a list of required addresses to the CPU which dumbly followed them is that the list was usually the same frame-to-frame as mode splits in general are rare, and mode splits that change the addressing are even rarer. So the most common operating case ...

Ada and Modula 2 are compiled languages that have coroutines and no garbage collection. (Then I thought, and surely Modula 3? But it doesn't.) If you're not fussed about garbage collection there are go and Haskell. Iterators in C# also work as a poor man's version. I guess real threads wouldn't be ...

I didn't have any sample files for the above tests. I just used the BASIC commands on the Acorn to output low/high frequency tones, then generated the same frequency tone in LTSpice. Although LTSpice does spit out a few wav files as part of running the simulation if that is what you're referring to...

This blog post might be of some help. I simulated the effects of those components when working on improving my FPGA Electron core's sound output. The oscilloscope waveforms from fpga were just not a good match to the real electron and those components were why. That blog is like catnip for me, than...

Does the 6845 ever test any value for anything other than exactly equal?

If the issue is just positioning being different, could it just be different assumptions about flyback? If that's a possibility, then the Dictionary of Video and Television Technology, p. 234 says that horizontal flyback will usually take about 7us, and vertical is typically in the range 500–750us. ...

Apologies from me too. Based on a quick check: it is loading while the screen is blank. So that's the timing discrepancy. If I turn off synthetic emulator fast loading, it is indeed blank for several minutes. For me, using the Stairway to Hell copy, it always launches to the select difficulty / load...