Search found 1271 matches

by Rich Talbot-Watkins
Sat Jul 21, 2018 10:25 am
Forum: general
Topic: *TAPE baud rates
Replies: 17
Views: 252

Re: *TAPE baud rates

My first computer was an Oric-1, which could load/save to tape at 2400 or 300 baud. 2400 baud never ever worked properly, so I always recorded at 300 baud, which even sounded slow. I never quite understood the Beeb cassette hardware. So the ULA has baud rate settings for transmit and receive, and th...
by Rich Talbot-Watkins
Fri Jul 20, 2018 11:06 am
Forum: hardware
Topic: 80 column teletext
Replies: 30
Views: 2683

Re: 80 column teletext

Nothing to do with me; this is Dominic's immense genius at work here!
by Rich Talbot-Watkins
Thu Jul 19, 2018 8:52 pm
Forum: hardware
Topic: 80 column teletext
Replies: 30
Views: 2683

Re: 80 column teletext

I assume it'd make the characters thinner with more space between them (I assume it's some kind of shift register which emits pixels one by one, and when it's over, it's blank). But here's another question: the teletext pixel clock is 6MHz but, with character rounding, it actually needs 12MHz for th...
by Rich Talbot-Watkins
Tue Jul 17, 2018 2:58 pm
Forum: development tools
Topic: Beebasm requests
Replies: 9
Views: 199

Re: Beebasm requests

For now I'd just be inclined to rewrite the macros within BeebAsm's limitations and change the 0s in the callsites to start+<whatever>. BeebAsm's maintained by the community here these days - I haven't touched it in years - so not sure when you might be able to get these changes in (although feel fr...
by Rich Talbot-Watkins
Tue Jul 17, 2018 12:00 pm
Forum: development tools
Topic: Beebasm requests
Replies: 9
Views: 199

Re: Beebasm requests

(Incidentally, I don't think this would be particularly different to implement either; A%..Z% could live in the symbol table like any other symbol, and be force created and initialized to zero at the beginning of each pass. Then the assignment code could make a special case of them. BeebAsm already ...
by Rich Talbot-Watkins
Tue Jul 17, 2018 11:56 am
Forum: development tools
Topic: Beebasm requests
Replies: 9
Views: 199

Re: Beebasm requests

Hey Kevin The problem with supporting mutable variables in BeebAsm is that, even though it is implemented as a two-pass assembler, it doesn't present itself as such. Thus when symbols are forward referenced, the expectation is that they will have unambiguously one and only one value. Seems to me tha...
by Rich Talbot-Watkins
Tue Jul 03, 2018 7:15 pm
Forum: programming
Topic: BBC Changing Coordinate system from 0-1024,0-1280
Replies: 12
Views: 671

Re: BBC Changing Coordinate system from 0-1024,0-1280

Apple ][ is 280x200 I believe (each character block is 7 pixels across, bizarrely). So it may well have come from Applesoft BASIC originally.
by Rich Talbot-Watkins
Thu Jun 28, 2018 2:14 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 544

Re: Expanding BBC BASIC on Acorn 8 bit machines

The reason is so that 'forward searches' (such as to find the ELSE in an IF clause) can be performed very efficiently, because you know you won't encounter the token for ELSE (in this case) in any other context. If you allow arbitrary binary constants to appear in a program, any such search needs t...
by Rich Talbot-Watkins
Thu Jun 28, 2018 12:48 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 544

Re: Expanding BBC BASIC on Acorn 8 bit machines

I've occasionally contemplated whether you could improve the performance of 6502 BBC BASIC by tokenising numeric literals. With an extra 16k of ROM there'd almost certainly be room to do that along with other features. I'd imagine replacing the ASCII representation of the number with a token byte, f...
by Rich Talbot-Watkins
Tue Jun 26, 2018 10:07 am
Forum: software: other
Topic: Any short type-ins for unattended Beebs?
Replies: 94
Views: 4138

Re: Any short type-ins for unattended Beebs?

In the third program edit line 60 to change the plus to a minus: - 60 PRINT CHR$(32+3*(C-INT(C)<.4)); + 60 PRINT CHR$(32-3*(C-INT(C)<.4)); I guess Apple BASIC uses +1 for TRUE. Yes, I also spotted that. There's also a boolean expression in line 40 which needs changing: - 40 A=ATN(Y/X)+(X<0)*SGN(Y)*...
by Rich Talbot-Watkins
Mon Jun 25, 2018 12:29 pm
Forum: emulators
Topic: emulator cycle vs walclock vs TIME accuracy
Replies: 8
Views: 491

Re: emulator cycle vs walclock vs TIME accuracy

From memory, I think B-Em scrimps on ADC emulation and doesn't generate and handle as many IRQs as real hardware. Have you compared with jsbeeb to see if you get more reasonable results? Also try turning off the ADC (*FX16) to see if that gives closer results on B-Em. Can't speak at all for BeebEm a...
by Rich Talbot-Watkins
Thu Jun 21, 2018 9:31 am
Forum: software: new games
Topic: New version of Scramble for the beeb (going well)
Replies: 64
Views: 3555

Re: New version of Scramble for the beeb (going well)

It's amazing to think how we did it back then: armed with just BBC BASIC with its built-in assembler, its clunky line editing, and ingenious ways of working around the memory limits. Matt and I did the first version of Blurp and a few other things like that, although we'd written a ROM which gave us...
by Rich Talbot-Watkins
Mon Jun 18, 2018 4:49 pm
Forum: stardot.org.uk
Topic: Post editing
Replies: 59
Views: 846

Re: Post editing

Another possibility is only allowing time-limited editing, apart from the first post of a topic, via this extension: https://www.phpbb.com/customise/db/extension/gn36_firstpostedit If you've already read a post, it's easy to miss any subsequent edits to it, so this doesn't seem like a bad idea to me...
by Rich Talbot-Watkins
Mon Jun 18, 2018 1:17 pm
Forum: stardot.org.uk
Topic: Post editing
Replies: 59
Views: 846

Re: Post editing

I have had a look over lunch, it does seem fairly easy to make a forum theme based on the current one that omits the edited message footer unless someone puts something in the reason box. If this sounds like it would mitigate most concerns then I'll put that into play this evening - it will require...
by Rich Talbot-Watkins
Mon Jun 18, 2018 7:55 am
Forum: stardot.org.uk
Topic: Post editing
Replies: 59
Views: 846

Re: Post editing

A good while back, I think the forum used to report all edits, and then this disappeared with one of the big upgrades. Since then, if I edit one of my own posts to add additional content or correct issues, I nearly always prefix it with 'Edit:' myself to make it clear that it's been added. I think t...
by Rich Talbot-Watkins
Tue Jun 12, 2018 3:38 pm
Forum: software: classic games
Topic: Acornsoft Labyrinth
Replies: 10
Views: 370

Re: Acornsoft Labyrinth

Cheers for the answer. However it looks a bit complicated for me. I am using a SD collection of games so looks like I need that specific drive with the game and load it manually? I do use special menu otherwise http://joxi.ru/v29Xeq1i3pY95m Yes - mount the disk image which contains Labyrinth and tr...
by Rich Talbot-Watkins
Tue Jun 12, 2018 3:36 pm
Forum: software: classic games
Topic: Acornsoft Labyrinth
Replies: 10
Views: 370

Re: Acornsoft Labyrinth

Any idea why that was done? :?: Maybe they thought it gave the graphics a strange swirly ethereal quality (which it certainly did on my TV) and thought it fitted the game. Or more likely it was just a mistake. It also has the effect of lowering the frame rate to 49.3fps but I doubt they did it to w...
by Rich Talbot-Watkins
Tue Jun 12, 2018 1:49 pm
Forum: software: classic games
Topic: Acornsoft Labyrinth
Replies: 10
Views: 370

Re: Acornsoft Labyrinth

Found it! This works on the Acornsoft release on the STH site - haven't tested any other versions.

Code: Select all

*LOAD LABRNTH
?&18D1=127
CALL&5D00
by Rich Talbot-Watkins
Tue Jun 12, 2018 1:39 pm
Forum: software: classic games
Topic: Acornsoft Labyrinth
Replies: 10
Views: 370

Re: Acornsoft Labyrinth

Yeah Labyrinth programs the video controller with non-standard values, specifically the horizontal timing is too long for a PAL display. My TV even used to have some small problems with it back in the day. It'll be easy enough to patch I suspect, but it'll need someone to find where CRTC R0 is writt...
by Rich Talbot-Watkins
Tue Jun 12, 2018 8:35 am
Forum: software: other
Topic: Any short type-ins for unattended Beebs?
Replies: 94
Views: 4138

Re: Any short type-ins for unattended Beebs?

timmy wrote:
Thu May 24, 2018 8:52 am
My school favourite was to do a quick:

Code: Select all

?&FE40=0:CLS
on all the machines before the teacher came and then sit down and wait for people to start typing...
What does that do? Enables sound chip writes at the same time as keyboard scan? It doesn't work on jsbeeb or B-Em... I wonder why? :-k
by Rich Talbot-Watkins
Fri Jun 08, 2018 3:10 pm
Forum: projects
Topic: 640x512 50 fps Bad Apple on a B... how?!
Replies: 28
Views: 989

Re: 640x512 50 fps Bad Apple on a B... how?!

Amazing the technology you can get these days.

Image
by Rich Talbot-Watkins
Fri Jun 08, 2018 1:25 pm
Forum: off-topic
Topic: Microsoft to buy Github
Replies: 30
Views: 622

Re: Microsoft to buy Github

I fully expect GitHub to end up with adverts everywhere though :( The annoying animating type that ended up all over Skype and MSN Messenger before it.
by Rich Talbot-Watkins
Thu Jun 07, 2018 7:10 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

A counter which is preloaded and counts down to zero is very much preferable - but the block diagram doesn't indicate that.) And indeed we know it not to be the case, as it's possible to change registers during the CRTC frame, and their new value will be correctly used as the upper bound. Are there...
by Rich Talbot-Watkins
Thu Jun 07, 2018 7:03 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

Just pondering this again this morning. I think, in terms of simplicity, everything makes sense apart from one thing. Are we sure that R12/13 take effect when set in the final scanline of the previous frame? Kieran, do you have concrete evidence of this working OK in your demo, or is there a chance ...
by Rich Talbot-Watkins
Wed Jun 06, 2018 10:58 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

This does make sense. Looking at the b-em source code it's doing approximately the following: IF HorizontalCharacterCount==R0 AND ScanlineCount==R9 AND VerticalCharacterCount==R4 THEN VerticalCharacterCount=0; FrameCount++ Presumably jsbeeb similar? What do we think that logic should look like? Bot...
by Rich Talbot-Watkins
Wed Jun 06, 2018 10:54 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

The easiest (and hence cheapest) counters have unsynchronised outputs. That is, propagation delay of the logic circuits causes the count to ripple through each stage, with the output of each stage changing one after another. This results in the output having invalid data for brief time periods. The...
by Rich Talbot-Watkins
Wed Jun 06, 2018 10:13 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

1024MAK wrote:
Wed Jun 06, 2018 9:35 am
Here is a diagram of a 74LS688 comparator from a TI datasheet:
Happy I guessed that right, at least :lol: Even if I didn't realise it would invert the inputs (or indeed the output!).
by Rich Talbot-Watkins
Wed Jun 06, 2018 10:00 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

There are some curious things I haven't yet figured. For example, the Scanline Counter has as its MC input: SLC==R9 OR (something from the Linear Address Generator). What can that be doing? Also interesting to note that the Linear Address Generator gets Hend as an input - this is so that it can cac...
by Rich Talbot-Watkins
Wed Jun 06, 2018 9:52 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

Looks like my interpretation of MC is wrong - thanks Mark. So MC will perform an immediate reset then. (Edit: although here 's an example of the sort of circuit I was imagining: a synchronous counter with a synchronous reset.) By the way, I think CC on the diagram is just another CO that's scanned b...
by Rich Talbot-Watkins
Wed Jun 06, 2018 9:48 am
Forum: emulators
Topic: Video Timing
Replies: 58
Views: 1989

Re: Video Timing

Edit: Mark just posted a load of great stuff, but going to post what I had here anyway, in reply to Ed! That sounds more complicated Ed! I assume a comparator is no more than a bunch of ANDed XNORs which surely can't have a prohibitively high transistor count. My mental model for this is as follows:...