Search found 188 matches

by ThomH
Fri Dec 09, 2016 1:59 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9251

Re: Composite video generation

Also from the repair guide, I was off about that phase counter. It's two independent signals in quadrature, not a direct counter. So it counts 00, 01, 11, 10. Close though. I still have a phase error in detecting the colour burst but here's the very first 'working' output based on throwing direct co...
by ThomH
Thu Dec 08, 2016 9:13 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9251

Re: Composite video generation

Seemingly confirmed. Indexing into that ROM is: apRG Bscc a = even or odd line; increments every sync p = is in back porch; stays high for a while after sync to effect the colour burst RGB = the colour channels s = sync, active high; cc = phase within the colour cycle, increments close to 1135 times...
by ThomH
Thu Dec 08, 2016 6:59 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9251

Re: Composite video generation

iss wrote:It's already in the old posts ;).
Oh, with an 'N'! That looked like a smudge on the photo I grabbed.

That's really cool. I'll be able to test my guesses about the meanings of the other lines and report back. I wish I were better at electronics.
by ThomH
Thu Dec 08, 2016 5:26 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 106
Views: 54817

Re: Yet Another

I've hatched off a different thread to enquire further about video generation. It looks like there's a lookup ROM involved and fairly limited precision on the colour subcarrier but I don't have a real machine or any idea how I would dump the thing even if I did so possibly that's a dead end. Being t...
by ThomH
Thu Dec 08, 2016 5:21 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9251

Composite video generation

I'm a circuit-reading dunce. Having opened with that, I was looking at the Oric schematic to try to learn a bit more about how composite video is generated. The relevant area seems to be along the top of the schematic, mostly to the right. First point of great interest: there's a 256x4 PROM involved...
by ThomH
Wed Dec 07, 2016 10:01 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 106
Views: 54817

Re: Yet Another

Separately, while looking into the "colours aren't right" issue, I've been grabbing some original television images from Youtube. It seems to vary from title to title but looking at the Manic Miner and Doggy as attached, there seems to be quite a lot of noise in some areas. If it's something the ori...
by ThomH
Wed Dec 07, 2016 6:00 pm
Forum: Technical questions
Topic: Does anybody have the WD1793 data sheet?
Replies: 6
Views: 7309

Re: Does anybody have the WD1793 data sheet?

Thanks! Those helped a lot. I won't bore you with the full litany of errors one could make by taking that "the WD1773 is 1793 compatible" statement too strictly but the absence of head loading logic is a lot of it. For the Microdisc, I settled upon signalling HLT 7,653,333/8,000,000ths of a second a...
by ThomH
Wed Dec 07, 2016 1:10 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 106
Views: 54817

Re: Yet Another

This looks cool. What about the colors - they seams to be very different from the real Oric? The video was taken in composite mode. But I don't know the signal specifics of the Oric so it's using a generic RGB -> composite encoder. So I might not be hitting the exact original colour encodings, but ...
by ThomH
Wed Dec 07, 2016 3:28 am
Forum: Games
Topic: Development of Blake's 7 (was OASIS development)
Replies: 600
Views: 390798

Re: OASIS development

I got my emulator seemingly into a working state, with an attempt at fully-correct timing. If you have a Mac, grab the binary from its thread and do as you wish. But if you don't have a Mac and there's anything I can do to help, please don't hesitate to ask.
by ThomH
Wed Dec 07, 2016 1:25 am
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 106
Views: 54817

Re: Yet Another

Updated again . New features of note: Microdisc emulation, intended to be timed accurately; better file analysis — should make a pretty good fist of deciding automatically between whether to launch a tape with the original ROM or the Atmos. This is based on a partial disassembly and inspection of t...
by ThomH
Tue Nov 29, 2016 5:17 pm
Forum: Games
Topic: Development of Blake's 7 (was OASIS development)
Replies: 600
Views: 390798

Re: OASIS development

My emulator implements real timing* but isn't quite ready yet; in a few weeks (or so) I or anybody else with a Mac can probably perform some basic timing tests if that'd be helpful. Sorry for the vague future offer — I thought maybe it was a bit more helpful to say something while the topic is activ...
by ThomH
Mon Nov 28, 2016 7:47 pm
Forum: Technical questions
Topic: A possible software alternative to Vsync?
Replies: 47
Views: 28807

Re: A possible software alternative to Vsync?

The numbers originally proposed, even if I hadn't mixed up multiplying by 40 and multiplying by 64, were predicated on a 260-line 60Hz frame. It turns out it's 264 lines. So the original arithmetic is based on false accounting, though the premise is still solid: leave a 60Hz attribute visible in a s...
by ThomH
Sun Nov 27, 2016 5:16 pm
Forum: Technical questions
Topic: Does anybody have the WD1793 data sheet?
Replies: 6
Views: 7309

Re: Does anybody have the WD1793 data sheet?

Yes, perfect, thanks! So it's call and response: the 1793 sets the HLD output upon receiving a command and proceeds only once the HLT input is set, for which the Microdisc has an LS123 and another part whose number I can't quite make out but which I assume together amount to: wait a fixed period. HL...
by ThomH
Sun Nov 27, 2016 2:59 pm
Forum: Technical questions
Topic: Does anybody have the WD1793 data sheet?
Replies: 6
Views: 7309

Does anybody have the WD1793 data sheet?

I'm specifically having difficulty chasing up the logic behind the HLD (head load, presumably?) pin, which per the Microdisc schematic is wired directly to the drives' motor on. Is there a spin-up sequence as there is when the 1770 and 1772 changes the motor on line (i.e. enable signal, wait for six...
by ThomH
Sat Nov 26, 2016 3:24 am
Forum: Technical questions
Topic: A possible software alternative to Vsync?
Replies: 47
Views: 28807

Re: A possible software alternative to Vsync?

312 and 264 are even better: the greatest common divisor of the two is 24 so unless I'm having a complete failure of logic you should be able to box yourself in to a 24-line period?