Search found 1135 matches

by Rich Talbot-Watkins
Fri Jan 19, 2018 10:32 am
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

Thanks again. I'd thought to try a similar idea for the sound but didn't really think of it for the video. When I started writing this, I thought that I'd need to handle all the screen updates in one go but it may well be quick enough to do them in real time. The only thing I can think of that the ...
by Rich Talbot-Watkins
Fri Jan 19, 2018 8:40 am
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

JetSetWilly is a good test of LDIR as it uses two screen buffers: sets up buffer 1, LDIRs it to buffer 2, writes sprites to it, then LDIRs it to the screen. A common emulation of LDIR is to do it atomically within the emulator, so to the CPU it looks like it's instant. The symptom of this is things...
by Rich Talbot-Watkins
Fri Jan 19, 2018 8:14 am
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

I have another thought about synchronising screen writes on the host with those on the emulator. This is still based on the assumption that the host will always be able to process packets from the parasite, on average, in real time. The issue is that we want to ensure that actual screen writes on th...
by Rich Talbot-Watkins
Thu Jan 18, 2018 9:45 pm
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

Just a further brain dump as I think of stuff. You might actually want to build in some delays on the parasite emulation so that you stay roughly in sync with real time at the end of every 8 lines or so. That would further mitigate flicker/tearing problems due to the host writing to the screen too s...
by Rich Talbot-Watkins
Thu Jan 18, 2018 9:37 pm
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

Just to add, for purposes of timing, it might be worth knowing that the Spectrum ULA didn't output interlaced video. It was just 312 lines each field, or exactly 69888 T-states.
by Rich Talbot-Watkins
Thu Jan 18, 2018 9:29 pm
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

I would think that your flicker is mostly caused by not syncing VSyncs on the host with your emulated HALT on the parasite. I would expect most games to use that to avoid flicker as much as possible, even those which have to present the back buffer via the SP or unrolled LDI techniques (as this can ...
by Rich Talbot-Watkins
Thu Jan 18, 2018 8:48 pm
Forum: hardware
Topic: SpectROM - Speccy emulator for the Pi co-pro
Replies: 54
Views: 1278

Re: SpectROM - Speccy emulator for the Pi co-pro

Just caught up with this thread. Great stuff Rob! On the subject of double buffering - I'm not sure it would be necessary, as I would have expected it to be possible to reflect the emulated screen state on the host in real time, as the emulation runs. You might need to make a few different cases for...
by Rich Talbot-Watkins
Wed Jan 17, 2018 8:13 pm
Forum: software: other
Topic: ASBAS Assembly Orientated BASIC
Replies: 5
Views: 201

Re: ASBAS Assembly Orientated BASIC

Wouldn't have really been useful for me - I used to use SIN/COS/SQR etc all the time for building tables and so on. In fact, that was one of my main reasons for writing BeebAsm in the first place - to have a 6502 cross assembler that could let me use these functions to build tables within my assembl...
by Rich Talbot-Watkins
Mon Jan 15, 2018 5:00 pm
Forum: programming
Topic: Many DEFPROC, 1 ENDPROC?
Replies: 17
Views: 1042

Re: Many DEFPROC, 1 ENDPROC?

If you want the compiler to be able to work out that it's safe to lift a strlen call out of a loop, you need it to know two things: ⋅ strlen() is a pure function (it has absolutely no side effects; it's impossible to tell if you called it once or twice) ⋅ The string its argument...
by Rich Talbot-Watkins
Mon Jan 15, 2018 2:30 pm
Forum: programming
Topic: 32k memory management for dummies
Replies: 28
Views: 755

Re: 32k memory management for dummies

OS 0.1 had *NOTAPE, which I assume deselected the filing system. Presumably they considered it useless enough to remove!
by Rich Talbot-Watkins
Mon Jan 15, 2018 2:21 pm
Forum: programming
Topic: Many DEFPROC, 1 ENDPROC?
Replies: 17
Views: 1042

Re: Many DEFPROC, 1 ENDPROC?

Of course, in this example, you'd be even better just writing: for (i = 0; s[i] != 0; i++) { x = s[i]; ... } to save iterating through the string twice (once in strlen, once in the loop). Edit: I previously stated that the compiler could be clever enough to hoist the strlen out of the loop if it mee...
by Rich Talbot-Watkins
Mon Jan 15, 2018 8:19 am
Forum: programming
Topic: BeebAsm's Hello World - printing part of file name, not "Hello World"
Replies: 13
Views: 327

Re: BeebAsm's Hello World - printing part of file name, not "Hello World"

tom_seddon wrote:I keep putting off thinking about this, but github sent me an email about the new PR, so I suppose I just have to admit it: I've been a terrible steward of this project :(

Not as bad as me! :lol:
by Rich Talbot-Watkins
Sun Jan 14, 2018 9:33 pm
Forum: programming
Topic: BeebAsm's Hello World - printing part of file name, not "Hello World"
Replies: 13
Views: 327

Re: BeebAsm's Hello World - printing part of file name, not "Hello World"

Erm, oops, yeah... my bad. I clearly wrote that help text as quickly as I wrote the initial release of BeebAsm. Sorry about that. Dunno who maintains the BeebAsm repo these days, but yeah feel free to get that changed. I guess I never expected anyone to ever try to assemble that (it was more of a &q...
by Rich Talbot-Watkins
Fri Jan 12, 2018 4:14 pm
Forum: software: other
Topic: Adventure games: written in assembler? What compression?
Replies: 6
Views: 300

Re: Adventure games: written in assembler? What compression?

You might be interested in the articles in Acorn User August and September 1988 on the adventure "The Warlord". The September article goes into some details about the engine it used (TAG), including examples of its scripting language and text compression techniques.
by Rich Talbot-Watkins
Fri Jan 12, 2018 2:40 pm
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

I just tried it: I replaced all the STA &359 with STA &36D and disabled the Master patch. Result? Hangs like the original version. So then I patched that LDA #&0E:STA &308 with LDA #0, and it no longer hangs, so that was the main problem. I have no idea why it was originally doing th...
by Rich Talbot-Watkins
Fri Jan 12, 2018 2:12 pm
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Incidentally, that weird code in the patch which is checking for certain magic values and converting them to other magic values: that's translating a 'stripy' colour value into the best flat colour that can be selected using a legal GCOL call. That's why stuff like the Witch's House roof looks flat ...
by Rich Talbot-Watkins
Fri Jan 12, 2018 1:47 pm
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Yes, I also just had a look at it. Seems like, on the Master, VDU variable &359 moved to &36D. On the Master &359 is "0 if plotting graphics foreground, 8 if plotting graphics background" - seems like any other value can make it hang completely! So they just replaced those writ...
by Rich Talbot-Watkins
Fri Jan 12, 2018 11:53 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Here's the 2 file (CITADEL and CITAX), no speech, no title screen, PIAS1 re-release BBC Master compatible disk version, which I guess would've been the last official release of the game :?: (CHAIN"CITADEL" to load!) There will in fact have been another version, as that's not Master Compac...
by Rich Talbot-Watkins
Fri Jan 12, 2018 11:40 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Just to further muddy the waters, in both the FDI and FSD 5681: lda #$01 5683: sta $54cf 5686: rts And in the original FDI we have: 54C5 LDA #&59 54C7 STA &06 54C9 LDA &1300,Y 54CC STY &01 54CE EOR &06 <-- self modified to EOR &01 by that code 54D0 STA &0400,Y 54D3 EOR &...
by Rich Talbot-Watkins
Fri Jan 12, 2018 10:05 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Here's the .fdi image for the original disk release of Citadel I was using, by the way. Use B-Em to load it.
by Rich Talbot-Watkins
Fri Jan 12, 2018 10:02 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

Well, none of the STH images are originals, because the SSD format can't support protected disks. So all of those images are necessarily versions which have had their protection stripped and put onto a clean DFS format disk image. The Citadel.ssd file on STH appears to be direct rip from tape of the...
by Rich Talbot-Watkins
Fri Jan 12, 2018 8:59 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

I just took a look at the original disk release. CITAL is a strange bit of code: in place of the NOPs there's a bunch of code which (after loading CITAM), reads the catalog info for CITAM, and then loads it again at its natural location. *INFO for CITAM looks like this: $.CITAM 008000 00A670 004100 ...
by Rich Talbot-Watkins
Fri Jan 12, 2018 8:29 am
Forum: software: classic games
Topic: Citadel Item Randomiser 0.1 (and now 0.2)
Replies: 28
Views: 1030

Re: Citadel Item Randomiser 0.1 (and now 0.2)

This looks like a transfer from tape ("Press Play" in the loader), and is a Master-compatible version, which means it contains the patch to move some code to Sideways RAM bank 5. I'm fairly sure that those NOPs are in the released version (I remember also being baffled by them when transfe...
by Rich Talbot-Watkins
Sat Jan 06, 2018 10:03 am
Forum: software: other
Topic: Tape protection systems
Replies: 67
Views: 5682

Re: Tape protection systems

Ahh hahaha, I forgot IRQ2V even existed! Don't think I ever used it in my life!

So, if the uef.hq has preserved the data correctly, the question is: what is it about the data which is not reading correctly in BeebEm, B-Em or jsbeeb? And have you figured out the basic mechanism of the protection?
by Rich Talbot-Watkins
Fri Jan 05, 2018 3:19 pm
Forum: software: other
Topic: Tape protection systems
Replies: 67
Views: 5682

Re: Tape protection systems

Yeah that's weird. The .hq.uef image from the old Acorn Preservation site is getting stuck after running ABBEY2 in the following place: 055f LDA #&00 0561 STA &76 0563 LDA &76 <-- 0565 BEQ &0563 <-- 0567 LDA #&00 0569 STA &76 No idea what is supposed to be changing &76 as...
by Rich Talbot-Watkins
Thu Jan 04, 2018 11:59 am
Forum: projects
Topic: New game - tube type thingy
Replies: 28
Views: 932

Re: New game - tube type thingy

Wow, what a fantastic idea - totally original, and the only thing which vaguely compares are those palette switching 'through the tunnel' demos, like Orlando's 3D Wars. This is of course far better, and I think it's fair to say that it's the first time I've seen perspective correct texturing on the ...
by Rich Talbot-Watkins
Sun Dec 31, 2017 2:58 pm
Forum: software: classic games
Topic: Unused Citadel bits
Replies: 42
Views: 1754

Re: Unused Citadel bits

Yeah, the screenshots I added upthread show that. The reason for it is that, for some reason, the triangle coordinates which make the roof are slightly off (the two bottom y coordinates are not equal). OS 1.20 has a small bug where triangles aren't plotted correctly in this case (it just plots the f...
by Rich Talbot-Watkins
Thu Dec 21, 2017 8:39 pm
Forum: software: classic games
Topic: Repton Infinity High Score Anagrams
Replies: 22
Views: 2654

Re: Repton Infinity High Score Anagrams

Codename Druid from Acorn User is another game by Daves Lawrence and Acton (credited to "Chris Ruseman"). And the high score name is LEO BRIEFCASE, which I can only assume is also an anagram. Also in the article itself are some odd names ("cumentexis" and "Brationst") ...
by Rich Talbot-Watkins
Fri Dec 15, 2017 10:58 am
Forum: stardot.org.uk
Topic: private messages
Replies: 12
Views: 391

Re: private messages

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by Rich Talbot-Watkins
Fri Dec 15, 2017 8:35 am
Forum: software: other
Topic: Wishful thinking - B+ OS, C/C++ DFS/ADFS
Replies: 16
Views: 604

Re: Wishful thinking - B+ OS, C/C++ DFS/ADFS

If memory serves, Exile uses the illegal opcodes while decrypting itself, and E-Type uses them for scaling graphics. This is a dim, distant memory from when I had implemented some of them incorrectly, way back in the '90s. Oooh, that's surprising, but also kinda cool. Obviously the Beeb versions ca...

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