Search found 1021 matches

by SarahWalker
Mon Jul 31, 2017 5:58 pm
Forum: other vintage computer hardware, software and games
Topic: Turbo XT
Replies: 2
Views: 161

Turbo XT

Inspired by Andy1979's 386 Restoration thread, and martinw's posts a while ago on his IBM XT, I thought I'd share my current project. A while ago I picked up a 10 MHz Turbo XT compatible board. Normally I'd play with this a little and then put it in the box with my other motherboards, I figured I'd ...
by SarahWalker
Wed Jul 26, 2017 4:15 pm
Forum: other vintage computer hardware, software and games
Topic: 386 Restoration
Replies: 7
Views: 323

Re: 386 Restoration

I find it odd that itt will only accept 4Mb of RAM IIRC the 386sx could address up to 16mb, and the motherboard has 8 sockets, so I would have thought that it should be able to access more. Though your simms do need to be fitted in pairs. It may be a genuine limitation, 386SX boards (particularly t...
by SarahWalker
Sat Jul 22, 2017 9:46 am
Forum: hardware
Topic: What would be a suitable D2A resister ladder for the beeb
Replies: 4
Views: 134

Re: What would be a suitable D2A resister ladder for the beeb

I used 10k resistors, and a 1uF electrolytic capacitor. I don't think the exact values matter too much, as long as all the resistors are the same! You shouldn't need anything else, it's a pretty basic circuit. If you haven't seen it, my schematic is at http://stardot.org.uk/forums/viewtopic.php?f=2&...
by SarahWalker
Wed Jul 19, 2017 4:50 pm
Forum: projects
Topic: Experiments in Stable Raster Timing
Replies: 14
Views: 701

Re: Experiments in Stable Raster Timing

Demo 128 also uses it, for the wobbly 50 fps rotozoomer at the end.
by SarahWalker
Mon Jul 17, 2017 5:11 pm
Forum: general
Topic: Archimedes 30th birthday?
Replies: 12
Views: 416

Re: Archimedes 30th birthday?

Isn't it the same PCB with different options fitted? At least between the A3xx and the original A440. I remember my 310 definitely having room for the hard disc controller. I think it also had something like 'UNIVERSAL BOARD' written on it somewhere.

The A4xx/1 was a different board.
by SarahWalker
Sat Jul 15, 2017 4:10 pm
Forum: projects
Topic: Experiments in Stable Raster Timing
Replies: 14
Views: 701

Re: Experiments in Stable Raster Timing

I had thought I was using both main & shadow RAM for the wavy test card, but a quick look at the source shows otherwise - it's using all 32kb of the shadow bank, to store a 128x128x4 (4kb) picture, but doesn't display the main bank. Obviously I thought at the time that non-integer scaling would ...
by SarahWalker
Sat Jul 15, 2017 10:19 am
Forum: projects
Topic: Experiments in Stable Raster Timing
Replies: 14
Views: 701

Re: Experiments in Stable Raster Timing

And here's another example that is resetting the screen address every scanline to achieve a classic Twister effect. Each line of the Twister is precalcuated and then we just select which line to "draw" every scanline. It's a lot faster to set a pointer to some memory than it is to actuall...
by SarahWalker
Sat Jul 15, 2017 10:14 am
Forum: software: new games
Topic: New Games Index
Replies: 23
Views: 836

Re: New Games Index

Some freeware stuff from me - I noticed the Atom ports of two of them have been posted but not the BBC originals : Hard Hat Harry - http://www.retrosoftware.co.uk/wiki/index.php?title=Hard_Hat_Harry Hard Hat Harry 2 - http://www.retrosoftware.co.uk/wiki/index.php?title=Hard_Hat_Harry_2 Jet Set Miner...
by SarahWalker
Wed Jun 21, 2017 6:23 pm
Forum: emulators
Topic: Which is the best BBC emulator to run on Windows 95?
Replies: 6
Views: 284

Re: Which is the best BBC emulator to run on Windows 95?

What are the specs of this machine?
by SarahWalker
Sat Jun 17, 2017 3:05 pm
Forum: emulators
Topic: Building B-em on Linux
Replies: 17
Views: 506

Re: Building B-em on Linux

You'll have to do a quick bit of source code modification. In linux.c, change the line

Code: Select all

if (key[KEY_F11]) gui_enter();

to

Code: Select all

if (key[KEY_ESC]) gui_enter();

and rebuild.
by SarahWalker
Sun Jun 04, 2017 9:22 pm
Forum: hardware
Topic: Riscstation R7500 video bandwidth
Replies: 2
Views: 128

Re: Riscstation R7500 video bandwidth

Should be the same as on an A7000+ : 80000000.
by SarahWalker
Sun Jun 04, 2017 7:23 pm
Forum: emulators
Topic: Games turn off interlace mode
Replies: 21
Views: 854

Re: Games turn off interlace mode

Hmm, must be misremembering then.It might work as I described on the Electron?
by SarahWalker
Sun Jun 04, 2017 11:54 am
Forum: emulators
Topic: Games turn off interlace mode
Replies: 21
Views: 854

Re: Games turn off interlace mode

You can determine odd/even field, by measuring the time between vsync. One field will appear to be one line longer than the other (I forget which one!).
by SarahWalker
Sat Jun 03, 2017 5:17 pm
Forum: off-topic
Topic: x86 Internals for Fun & Profit
Replies: 12
Views: 495

Re: x86 Internals for Fun & Profit

Well, ARM do make CPUs with and without this complexity - the A53 is entirely compatible with the bigger A57/A72/A73 CPUs, but removes most of the additional complexity in order to hit much smaller area and power targets; it's in-order, has only the most basic super-scalar functionality (only two in...
by SarahWalker
Sat Jun 03, 2017 11:26 am
Forum: off-topic
Topic: x86 Internals for Fun & Profit
Replies: 12
Views: 495

Re: x86 Internals for Fun & Profit

I think strictly speaking, most of the complexity is an attempt to hide latency. Also attempting to extract as much parallelism as possible from something that's fundamentally serial.
by SarahWalker
Mon May 22, 2017 4:57 pm
Forum: hardware
Topic: Question about MEMC translation tables reprogramming
Replies: 12
Views: 362

Re: Question about MEMC translation tables reprogramming

You can't disable MEMC translation - it's always enabled for the bottom 32 MB of the address space. You could avoid it by only using the linear physical mapping between 32 MB and 48 MB. But this won't actually gain you anything in terms of performance, as the MEMC translation doesn't incur any penal...
by SarahWalker
Wed May 10, 2017 9:14 pm
Forum: hardware
Topic: Burning a RISC OS 2.01 EPROM
Replies: 7
Views: 226

Re: Burning a RISC OS 2.01 EPROM

2.01 also adds support for 16 MB of RAM.
by SarahWalker
Mon Apr 17, 2017 4:13 pm
Forum: hardware
Topic: was the Master originally proposed with a 65816?
Replies: 3
Views: 304

Re: was the Master originally proposed with a 65816?

One of the parts of history of Acorn that is would be interesting to find out more about. Others would include the decision to cripple the Electron's DRAM memory performance by launching the machine with four instead of eight 64kbitx1 memory chips, when eight would have given Acorn a machine with m...
by SarahWalker
Mon Apr 17, 2017 3:59 pm
Forum: hardware
Topic: Printer port DAC
Replies: 1
Views: 172

Re: Printer port DAC

I'm guessing that I can't have been the first person to hook up a DAC to the printer port, but I'm unaware of any commercial products to that end. B-em is outputting at 31250 Hz, but for various reasons (largely crap design and programming on my part!) is actually sampling sound data at half that. S...
by SarahWalker
Wed Apr 12, 2017 5:09 pm
Forum: emulators
Topic: Do you own a Mac, and like your Electron emulators minimal and potentially seizure-inducing?
Replies: 54
Views: 3182

Re: Do you own a Mac, and like your Electron emulators minimal and potentially seizure-inducing?

The repeating patterns are a result of the Beeb's pixel clock (4 MHz in MODE 2) not being synchronised with the PAL colour burst (4.43 MHz). This results in crosstalk between the luminance and chroma signals giving you the wobbly rainbow dot crawl. B-em also does this when using PAL emulation, thoug...
by SarahWalker
Fri Apr 07, 2017 6:40 pm
Forum: software: other
Topic: Increasing colour depth by flipping differently dithered screens
Replies: 9
Views: 456

Re: Increasing colour depth by flipping differently dithered screens

I think the Beeb's limited palette makes this too flickery to be usable - you've essentially switching R/G/B between full-on and full-off, and the average Beeb monitor (or TV) doesn't have enough persistence to make this tolerable. The CoCo 3 has a 64 colour palette, which will work better on the av...
by SarahWalker
Sat Apr 01, 2017 7:06 am
Forum: hardware
Topic: Acorn system questions :)
Replies: 6
Views: 413

Re: Acorn system questions :)

Yes. Bandwidth is 25.6 MB/sec on 8 MHz bus systems (Archimedes 300/400/A3000), 38.4 MB/sec on 12 MHz (all the others). Why 25,6MB/sec / 38,4MB/sec - my calculation is fault i think :-) i multiplied the bus specifications naively (wide x speed) :D Now i know its wrong i missed the timings or why 25,...
by SarahWalker
Fri Mar 31, 2017 9:29 pm
Forum: hardware
Topic: Acorn system questions :)
Replies: 6
Views: 413

Re: Acorn system questions :)

1. 32 Bit System - RAM ist also 32 Bit wide ? (4 (32Bit) x 8MHz = 32 MByte/sec gross ?) Yes. Bandwidth is 25.6 MB/sec on 8 MHz bus systems (Archimedes 300/400/A3000), 38.4 MB/sec on 12 MHz (all the others). 2. 8BPP Mode - i just saw in the datasheet the VIDC has 16 Color register right ? It is poss...
by SarahWalker
Sat Mar 25, 2017 9:43 pm
Forum: other vintage computer hardware, software and games
Topic: CGA in 1024 Colors - a New Mode: the Illustrated Guide
Replies: 7
Views: 421

Re: CGA in 1024 Colors - a New Mode: the Illustrated Guide

Artifact colours would never be stable on the Beeb - the pixel clock (16 MHz) is completely unrelated to the colour subcarrier (4.43 MHz). All you get is a shifting rainbow pattern as a result.

On CGA, the pixel clock is exactly 4x the NTSC colour subcarrier, hence artifact colours are stable.
by SarahWalker
Fri Mar 24, 2017 6:38 pm
Forum: other vintage computer hardware, software and games
Topic: CGA in 1024 Colors - a New Mode: the Illustrated Guide
Replies: 7
Views: 421

Re: CGA in 1024 Colors - a New Mode: the Illustrated Guide

This sort of thing is part of the reason I was telling martinw to keep his IBM XT hooked up via composite.
by SarahWalker
Mon Mar 20, 2017 5:57 pm
Forum: other vintage computer hardware, software and games
Topic: IBM PC XT
Replies: 20
Views: 730

Re: IBM PC XT

Very nice!

It might be worth sticking with composite for now - there are quite a few games that support 16 colours on composite CGA.
by SarahWalker
Sun Mar 19, 2017 9:28 pm
Forum: emulators
Topic: Building RPCEmu on Mac OS X
Replies: 15
Views: 830

Re: Building RPCEmu on Mac OS X

Yes, using a modern version of Allegro is a great idea. Although I'm not a developer, I have always wondered why RPCEmu and Arculator used such an old version. I assumed it was more complicated than just changing a few references so that must be the reason. Allegro 5 wasn't available during the ori...
by SarahWalker
Sun Mar 19, 2017 9:25 pm
Forum: emulators
Topic: B-Em and Allegro 5
Replies: 9
Views: 517

Re: B-Em and Allegro 5

The B-Em Linux UI uses the Allegro 4 Menus/Dialogs API, where as the B-Em Windows UI I think bypasses Allegro and uses Windows APIs directly. I'd like to better understand the rationale for that split, as it means the Menus are implemented twice. The Windows native menu is there because the Allegro...
by SarahWalker
Fri Mar 10, 2017 10:46 pm
Forum: projects
Topic: MODE 7 Vertical Rupture
Replies: 31
Views: 1266

Re: MODE 7 Vertical Rupture

Actually, that's another question - how does interlaced sync and video work in this case? By ramming two CRTC frames into a single PAL refresh, are you getting odd and even fields in the same refresh, or does the SAA chip also determine odd/even by some other means (e.g. counting VSyncs and alterna...

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