Search found 1005 matches

by SarahWalker
Mon May 22, 2017 4:57 pm
Forum: hardware
Topic: Question about MEMC translation tables reprogramming
Replies: 12
Views: 214

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: 143

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: 244

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: 129

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: 49
Views: 2626

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: 341

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: 335

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: 335

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: 316

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: 316

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: 573

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: 523

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: 383

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: 965

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...
by SarahWalker
Thu Mar 09, 2017 10:24 pm
Forum: projects
Topic: MODE 7 Vertical Rupture
Replies: 31
Views: 965

Re: MODE 7 Vertical Rupture

I'm still slightly confused as to how interlace applies to the Beeb though, please forgive me. Given that any PAL signal has 625 lines split across two interlaced fields, but the Beeb can only output 312 lines, what exactly is the effect of turning interlace on or off for MODES 0-6? Presumably we'r...
by SarahWalker
Wed Mar 08, 2017 9:25 pm
Forum: emulators
Topic: MAME: Emulating FDC Boards
Replies: 36
Views: 1781

Re: MAME: Emulating FDC Boards

This still doesn't really explain the delay before issuing the Force Interrupt command, though, so I'm suspicious that there's something I'm missing, and/or there's something else I'm still not doing properly. I would guess it's giving time for the FDC to read and check the CRC before cancelling th...
by SarahWalker
Tue Mar 07, 2017 9:15 pm
Forum: software
Topic: Unreleased games
Replies: 13
Views: 513

Re: Unreleased games

Frak 2 is mentioned as a BBC isometric thingy in Stairway To Hell's Lost+Found section.
by SarahWalker
Tue Mar 07, 2017 6:00 pm
Forum: software
Topic: Unreleased games
Replies: 13
Views: 513

Unreleased games

I was digging through some of my old files recently, and found a list of unreleased games that I'd collated from various sources (mainly Usenet), with a view to making a "Games That Weren't" site that never happened. Thought I'd post the list here. Does anyone have any more knowledge about...
by SarahWalker
Mon Feb 27, 2017 5:51 pm
Forum: software: other
Topic: BeebOPL choons
Replies: 45
Views: 1965

Re: BeebOPL choons

That was with the Beeb sound chip playing back samples. A real DAC should be a lot louder!
by SarahWalker
Sat Feb 25, 2017 8:39 pm
Forum: software: other
Topic: BeebOPL choons
Replies: 45
Views: 1965

Re: BeebOPL choons

See attached crap diagram. R is 10k on my DAC.
by SarahWalker
Sat Feb 25, 2017 7:25 pm
Forum: software: other
Topic: BeebOPL choons
Replies: 45
Views: 1965

Re: BeebOPL choons

More than two months since my last release! To make up for it : Here's Zone 66. Another Epic release from 1993, this democoder-authored game uses the CDFM engine, to combine 9 voices of OPL with 4 voices of samples. This is a bit of a stretch for the Beeb, so there are three versions here. The stand...
by SarahWalker
Sat Feb 25, 2017 8:05 am
Forum: emulators
Topic: B-Em
Replies: 272
Views: 7821

Re: B-Em

Apart from file selection, none of the UI needs to be native. Instead of targeting Windows or Linux, why not make it BBC Micro style? Probably worth noting that B-em had a non-native UI prior to v0.8, largely due to DOS still being the primary target. The general feedback I got was that people hate...
by SarahWalker
Sun Feb 19, 2017 10:41 am
Forum: other vintage computer hardware, software and games
Topic: Superior Software's Speech on the Commodore 64
Replies: 4
Views: 288

Re: Superior Software's Speech on the Commodore 64

Yep, you loose ~40 cycles (depending on what sprites are enabled) every 8 lines to VIC-II. This isn't a show-stopper, but I suppose Superior decided that the audio quality was too poor with the display enabled, and that it probably wasn't worth working around it.
by SarahWalker
Sun Feb 12, 2017 3:03 pm
Forum: hardware
Topic: A5000 Overclock
Replies: 4
Views: 216

Re: A5000 Overclock

I did run one at 30 MHz ARM3 + 16.66 MHz memory for a while, and it seemed perfectly stable. There may have been more headroom on the CPU, but I didn't have appropriate oscillators to test. The memory clock was at it's limit though - I tried 17.3 MHz and it had 'issues'.
by SarahWalker
Thu Feb 09, 2017 6:19 pm
Forum: off-topic
Topic: What is the average age on here??
Replies: 194
Views: 11805

Re: What is the average age on here??

Beebs were still in use at my primary school when I left in 1998. They were still in occasional use at my secondary school when I started, but got phased out there after a year or two. There was one used from time to time in my A-level Physics class, about 2003.
by SarahWalker
Wed Feb 08, 2017 8:53 pm
Forum: software: games
Topic: Playing Tetris got me thinking...
Replies: 13
Views: 586

Re: Playing Tetris got me thinking...

Could it be worth looking at the CGA version of Tetris (that I remember well albeit via a monochrome Hercules emulation of CGA) as that is based on a four colour mode with similar(ish) resolutions as the BBC/elec? Possibly worth mentioning that the background graphics on the EGA and Tandy versions ...
by SarahWalker
Mon Feb 06, 2017 5:40 pm
Forum: software: other
Topic: A mathematical demo and the request for help from the hardware owners
Replies: 69
Views: 3452

Re: A mathematical demo and the request for help from the hardware owners

BigEd wrote:??? But the Spectrum is clocked slower than the Amstrad, isn't it?

Amstrad has to deal with memory contention, the Spectrum doesn't outside of the first 16kb. So the Speccy is slightly faster overall.
by SarahWalker
Thu Jan 19, 2017 6:38 pm
Forum: projects
Topic: MODE 7/75
Replies: 19
Views: 706

Re: MODE 7/75

Rich Talbot-Watkins wrote:[*] Or does it just assume characters of 10 scanlines? How does it synchronise the start of the frame in that case?

Looks to be the DEW pin, which is connected to VSYNC on the 6845.
by SarahWalker
Mon Jan 09, 2017 8:08 pm
Forum: general
Topic: the best 8-bit computer...
Replies: 27
Views: 908

Re: the best 8-bit computer...

It's got a bigger palette, 27 colours instead of 8+flashing, or 4096 on the CPC+.

The Commodore 128D has better pixel graphics though - 640x200x16. In terms of colour, the MSX2+ can do 256x212x19268.

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