Search found 458 matches

by ThomasHarte
Wed May 16, 2018 2:04 am
Forum: emulators
Topic: Clock Signal: now also for Linux and BSD
Replies: 15
Views: 1114

Re: Clock Signal: now also for Linux and BSD

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...
by ThomasHarte
Sun May 13, 2018 3:35 pm
Forum: software: other
Topic: SN76489 best sample playback?
Replies: 44
Views: 1194

Re: SN76489 best sample playback?

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.
by ThomasHarte
Sat May 12, 2018 4:04 pm
Forum: software: other
Topic: SN76489 best sample playback?
Replies: 44
Views: 1194

Re: SN76489 best sample playback?

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...
by ThomasHarte
Fri May 11, 2018 9:07 pm
Forum: software: other
Topic: SN76489 best sample playback?
Replies: 44
Views: 1194

Re: SN76489 best sample playback?

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...
by ThomasHarte
Fri May 11, 2018 6:39 pm
Forum: software: other
Topic: SN76489 best sample playback?
Replies: 44
Views: 1194

Re: SN76489 best sample playback?

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...
by ThomasHarte
Fri May 11, 2018 2:05 pm
Forum: software: other
Topic: SN76489 best sample playback?
Replies: 44
Views: 1194

Re: SN76489 best sample playback?

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...
by ThomasHarte
Wed May 09, 2018 3:43 pm
Forum: emulators
Topic: b2 - new emulator
Replies: 91
Views: 7005

Re: b2 - new emulator

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 ...
by ThomasHarte
Tue May 08, 2018 8:15 pm
Forum: emulators
Topic: b2 - new emulator
Replies: 91
Views: 7005

Re: b2 - new emulator

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 ...
by ThomasHarte
Thu May 03, 2018 5:05 pm
Forum: hardware
Topic: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?
Replies: 10
Views: 678

Re: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?

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...
by ThomasHarte
Thu May 03, 2018 2:54 pm
Forum: hardware
Topic: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?
Replies: 10
Views: 678

Re: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?

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...
by ThomasHarte
Sat Apr 21, 2018 5:11 pm
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1811

Re: Video Timing

Does the 6845 ever test any value for anything other than exactly equal?
by ThomasHarte
Sat Apr 21, 2018 6:08 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1811

Re: Video Timing

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. ...
by ThomasHarte
Wed Apr 18, 2018 11:03 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

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...
by ThomasHarte
Wed Apr 18, 2018 10:11 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

Obviously this could very easily be an emulation problem, but having inserted the Southern Belle ROMs in reverse order so that they'd load, I actually got a worse-than-Elkulator output as attached. So in the configuration I tried, the only ROMs present are the OS, BASIC and the two Southern Belle RO...
by ThomasHarte
Wed Apr 18, 2018 9:55 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

You might also want to try the other ROMs I posted earlier to see if they also work in Clock Signal, Thomas. ;) Assuming this is of the smoothness intended, success! I'm about to test Southern Belle, but have discovered a bug in inserting a second ROM. So will be back to comment on that in the near...
by ThomasHarte
Wed Apr 18, 2018 3:39 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

If you want to send a modified ROMFS copy to test in Clock Signal, I can definitely do that. It runs the tape-based Southern Belle and everything else I've ever thrown at it correctly.
by ThomasHarte
Wed Apr 18, 2018 12:59 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

I quickly created a disc image for testing. I'm not sure how useful it will be. Thanks, but worse then Elkulator, I get nothing but a blank screen. I'll re-visit it when I can load it from UEF. Make sure you've got the tape interface implemented correctly; if memory serves then it puts the tape har...
by ThomasHarte
Mon Apr 16, 2018 1:17 pm
Forum: emulators
Topic: MAME: Video handling
Replies: 38
Views: 2139

Re: MAME: Video handling

Sorry, I've used '100Hz interrupt' as an incorrect term for the real-time clock interrupt, because it plus display end are used to produce the 100Hz interrupt offered to paged ROMs. So I've managed simultaneously to be both misleading and factually incorrect. It's a 50Hz interrupt. As I treat Paul B...
by ThomasHarte
Thu Apr 12, 2018 3:10 pm
Forum: hardware
Topic: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?
Replies: 10
Views: 678

Re: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?

Thanks! These facts I shall attempt to internalise. If it's not too much of a divergence, I read elsewhere that "[w]herever a voltage is artificially held away from zero, there will be leakage and the actual output will decay towards zero at a rate proportional to the offset from zero: dV/dt = -kV"....
by ThomasHarte
Wed Apr 11, 2018 7:45 pm
Forum: hardware
Topic: Electron: net purpose of Q3, Q4, R66, R67, C11, C25?
Replies: 10
Views: 678

Electron: net purpose of Q3, Q4, R66, R67, C11, C25?

I am a dunce. I am an electronics dunce. I was nevertheless browsing the Electron schematic and noticed these components sitting in a conflagration between the ULA's SOUND O/P and the speaker — on that schematic they're all just slightly to the right of the ULA, not quite halfway down. It looks like...
by ThomasHarte
Tue Apr 10, 2018 2:54 pm
Forum: emulators
Topic: Which Emulator for BBC Micro on Linux?
Replies: 37
Views: 1624

Re: Which Emulator for BBC Micro on Linux?

Seconded for B2! Thomas could you expand on that? ... The issue with Allegro as an awkward dependency AFAIK only applies to Allegro 4. There is now an Allegro 5 port of B-Em and Allegro 5 is available pre-compiled for Windows and as a Visual Studio Nugget. For me it's a lot about being able to use ...
by ThomasHarte
Mon Apr 09, 2018 5:45 pm
Forum: emulators
Topic: Which Emulator for BBC Micro on Linux?
Replies: 37
Views: 1624

Re: Which Emulator for BBC Micro on Linux?

Seconded for B2!

Re: awkward dependencies, per the repository it's not in any way an Allegro project. There are other dependencies too, but it's SDL for video.
by ThomasHarte
Wed Apr 04, 2018 5:37 pm
Forum: software & utilities for the pc, mac or unix
Topic: iOS edition of BBC BASIC announced
Replies: 38
Views: 1615

Re: iOS edition of BBC BASIC announced

The limit of 100 devices of each type for 'ad hoc' distribution is likely to be far greater than the demand (it certainly is at the moment) and the administrative overhead is minimal. Right, I've probably been overly-influenced by my experience of doing this for beta releases in larger companies; w...
by ThomasHarte
Fri Mar 23, 2018 1:47 pm
Forum: software & utilities for the pc, mac or unix
Topic: iOS edition of BBC BASIC announced
Replies: 38
Views: 1615

Re: iOS edition of BBC BASIC announced

Sorry, minor diversion to loop back to the Apple issue: did you consider just using TestFlight for distribution? The disadvantage is that it's a similar review process as for the App Store proper (albeit with relaxed stability and completeness requirements, speaking empirically), but the advantage i...
by ThomasHarte
Fri Mar 23, 2018 1:11 pm
Forum: emulators
Topic: MAME: Electron MRB
Replies: 6
Views: 618

Re: MAME: Electron MRB

I'm being such a dunce in this thread that I almost hesitate to respond again, but... I've implemented as per Sarah's post http://stardot.org.uk/forums/viewtopic.php?f=54&t=12242&p=155982#p155638 and the OS 3.00 displays accordingly. Then I guess it's testing the memory map rather than expecting the...
by ThomasHarte
Fri Mar 23, 2018 2:19 am
Forum: emulators
Topic: Clock Signal: now also for Linux and BSD
Replies: 15
Views: 1114

Re: Clock Signal: now also for Linux and BSD

Very minor announcement: a new release enables HFE support for the Electron. So if you have any disk images in that format, or create any because you have an HxC, please don't hesitate to test.

As I've yet to implement FDI or anything equivalent, HFE is now the most accurate supported file format.
by ThomasHarte
Thu Mar 22, 2018 5:13 pm
Forum: emulators
Topic: MAME: Electron MRB
Replies: 6
Views: 618

Re: MAME: Electron MRB

I can answer only as far as covered here , which covers behaviour when in shadow mode — most recent PC address (latched upon SYNC) plus the value written to 0xfc7f dictate visibility. Thanks, actually found that thread around the same time you posted last night. Anyway, both Turbo and Shadow modes ...
by ThomasHarte
Thu Mar 22, 2018 2:42 am
Forum: emulators
Topic: MAME: Electron MRB
Replies: 6
Views: 618

Re: MAME: Electron MRB

I can answer only as far as covered here, which covers behaviour when in shadow mode — most recent PC address (latched upon SYNC) plus the value written to 0xfc7f dictate visibility.

I don't recall offhand how shadow or turbo mode is detected at runtime, if it isn't just a ROM substitution.
by ThomasHarte
Wed Mar 21, 2018 12:06 am
Forum: archive issues
Topic: Electron to BBC Conversions
Replies: 42
Views: 3417

Re: Electron to BBC Conversions

I checked, and it is Flight Path 737 I was thinking of, as attached. 'Flying Experience' and 'Select Level (1 to 6)' are Mode 1; the six numbered options are Mode 4 with busy wait palette changes. So that's all eight colours on a 320px width display. I think possibly a developer found himself with a...
by ThomasHarte
Tue Mar 20, 2018 8:33 pm
Forum: archive issues
Topic: Electron to BBC Conversions
Replies: 42
Views: 3417

Re: Electron to BBC Conversions

Sorry, I was on holiday! The Electron's 6502: runs at 2Mhz when accessing ROMs in any mode; runs at 1Mhz when accessing RAM in modes 4–6, regardless of the current raster position; runs at 1Mhz when accessing RAM in modes 0–3 if pixels are not currently being output; if pixels are currently being ou...