Search found 131 matches

by jregel
Thu Aug 15, 2019 9:54 pm
Forum: hardware
Topic: BBC clock speed
Replies: 23
Views: 669

Re: BBC clock speed

Obviously there is the implication that each pixel takes two cycles, but can anyone explain what’s happening (or if I’m completely off track here)? You're sort of on the right track but you've forgotten about the borders :) If you look at p. 361 of the Beeb Advanced User Guide, you'll see that regi...
by jregel
Thu Aug 15, 2019 6:05 pm
Forum: hardware
Topic: BBC clock speed
Replies: 23
Views: 669

Re: BBC clock speed

Thanks again for all the comments. It’s taken a while for me to absorb it and do some more background reading… One follow-on question: The CRTC runs at 2Mhz when displaying the high resolution modes. So, in mode 0, there are 640 * 1bit pixels = 80bytes per scanline. There are 256 scanlines = 20480 b...
by jregel
Wed Aug 07, 2019 4:40 pm
Forum: hardware
Topic: BBC clock speed
Replies: 23
Views: 669

Re: BBC clock speed

Thanks again, everyone, both for the answers and bearing with my questions! I'm reading through all the replies and trying to get a handle on how it works. As Mark (1024MAK) recognised, I was seeing it a bit like a microprocessor, and find the bingo example helpful. Numerous comments have used the p...
by jregel
Wed Aug 07, 2019 1:30 pm
Forum: hardware
Topic: BBC clock speed
Replies: 23
Views: 669

Re: BBC clock speed

Thanks for all the replies! So am I right in understanding that the 6845 is the only other chip that reads from RAM, and that is writes a stream of bytes to the Video ULA? This occurs at either 1Mhz or 2Mhz, depending on screen mode. Why does the Video ULA need to run at 16Mhz? Is this related to do...
by jregel
Tue Aug 06, 2019 1:02 pm
Forum: hardware
Topic: BBC clock speed
Replies: 23
Views: 669

BBC clock speed

I’m trying to get a better handle on how the BBC works, in terms of its clock speed. The RAM in the BBC is clocked at 4Mhz. The 6502 is clocked at 2Mhz, so there is a further 2 million clock cycles that could be used to read/write RAM when the 6502 isn’t accessing it. How is this non-CPU time alloca...
by jregel
Thu Jul 18, 2019 9:20 pm
Forum: software: other
Topic: VDU 23,26
Replies: 3
Views: 272

Re: VDU 23,26

RobC wrote:
Thu Jul 18, 2019 8:23 pm
I haven't got access to my Communicator at the moment but there's some documentation here as it was carried over to Arthur/RISC OS.
Thanks Rob, that's interesting.

Sounds as if the Communicator was able to display different fonts on screen at the same time?
by jregel
Thu Jul 18, 2019 7:02 pm
Forum: software: other
Topic: VDU 23,26
Replies: 3
Views: 272

VDU 23,26

VDU 23,26 is described in the New Advanced User Guide as:

"reserved for Communicator font changes"

Does anyone know what these font changes were?
by jregel
Thu Mar 21, 2019 8:47 pm
Forum: software: new games
Topic: Stunt Car Racer for BBC Master
Replies: 60
Views: 3612

Re: Stunt Car Racer for BBC Master

A great review on ChinnyVision's YouTube page.

He does throw the gauntlet down for a Starglider port... :-)
by jregel
Wed Mar 20, 2019 8:59 am
Forum: software: new games
Topic: Doom?
Replies: 123
Views: 6264

Re: Doom?

Thanks Rob.

It's incredibly impressive that you have been able to build on top of the routines provided by the MOS and extend them in such an elegant way. It really does show how well the original API was designed.
by jregel
Mon Mar 18, 2019 8:26 pm
Forum: software: new games
Topic: Doom?
Replies: 123
Views: 6264

Re: Doom?

Thanks Rob. Absolutely happy to share what I've done with anyone who wants to do the same thing. It would be great to see other people do stuff for the Pi. For the C on the Pi side of things, I've got some newlib stubs for the standard library functions and code that allows access to SWIs etc. I use...
by jregel
Sun Mar 17, 2019 8:55 pm
Forum: software: new games
Topic: Doom?
Replies: 123
Views: 6264

Re: Doom?

Another really exciting development, Rob! Look forward to seeing how far you take this, and the surely inevitable interview in Retrogamer magazine... :-) As someone who, with this and your Spectrum and Amstrad CPC emulators, has pushed the delivery of graphics from a co-pro to the host, would you co...
by jregel
Sat Mar 16, 2019 3:57 pm
Forum: for sale / freebies
Topic: Free Book: An Expert Guide
Replies: 6
Views: 586

Re: Free Book: An Expert Guide

I recently picked up a copy of this book. While I'm sure many on here will already own a copy, if you haven'tm it's definitely worth getting.
by jregel
Tue Mar 12, 2019 3:02 pm
Forum: programming
Topic: 6502, 65SC12, 65C102, huh?
Replies: 8
Views: 658

Re: 6502, 65SC12, 65C102, huh?

One clarification: The Master uses a Rockwell 65SC12, which adds the 12 new instructions, and addressing modes, from the second processor’s 65C02. Both my Masters use a CMD/GTE G65SC12, which doesn't include RMB/SMB/BBR/BBS. Datasheet is here: http://archive.6502.org/datasheets/cmd_g65scxxx_mpu_fam...
by jregel
Mon Mar 11, 2019 9:09 pm
Forum: programming
Topic: 6502, 65SC12, 65C102, huh?
Replies: 8
Views: 658

Re: 6502, 65SC12, 65C102, huh?

dp11 wrote:
Sun Mar 10, 2019 11:03 pm
jregel wrote:
Sun Mar 10, 2019 10:50 pm
Does the 6502 emulation provided by the PiTubeDirect support the Rockwell instructions?
Yes it does.
Thanks for the clarification!
by jregel
Mon Mar 11, 2019 6:44 pm
Forum: programming
Topic: 6502, 65SC12, 65C102, huh?
Replies: 8
Views: 658

Re: 6502, 65SC12, 65C102, huh?

I believe the B+ has a 2Mhz Rockwell 6512A.

I'd assume it runs BASIC II, since it precedes the Master...?
by jregel
Sun Mar 10, 2019 10:50 pm
Forum: programming
Topic: 6502, 65SC12, 65C102, huh?
Replies: 8
Views: 658

6502, 65SC12, 65C102, huh?

I’ve been doing some reading up around the different CPUs found in the different BBC models and would like to check my understanding is correct: BBC Model A and B Original BBC Model B has a MOS 6502A (NMOS). External 6502 Second Processor The external 6502 Second Processor uses a Rockwell 65C02 (CM...
by jregel
Thu Mar 07, 2019 10:17 pm
Forum: software: new games
Topic: New game for the BBC Master : Planet Nubium
Replies: 41
Views: 5263

Re: New game for the BBC Master : Planet Nubium

I spent a bit of time this evening playing Planet Nubium. Really good game, different from, but obviously very reminiscent of Manic Miner. Great job!
by jregel
Thu Mar 07, 2019 7:40 pm
Forum: projects
Topic: Starting a port of Stunt Car Racer...
Replies: 34
Views: 3031

Re: Starting a port of Stunt Car Racer...

I've already commented on the YouTube page, but it's worth repeating and adding to. Along with the Prince of Persia port, and other titles like Planet Nubium, it feels like we're finally starting to see what was the Master was capable of.
by jregel
Tue Mar 05, 2019 4:31 pm
Forum: programming
Topic: Newbie 6502 assembly questions...
Replies: 25
Views: 1369

Re: Newbie 6502 assembly questions...

Thanks Tricky. I'm nowhere near running out of memory yet, just trying to get a firmer understanding about how to do things right, primarily around how BASIC and the assembler interact.
by jregel
Mon Mar 04, 2019 10:42 pm
Forum: hardware
Topic: VideoNuLA survey
Replies: 10
Views: 552

Re: VideoNuLA survey

I've got an original Master with internal co-processor, with a Datacentre (with CF cards, so I put down hard disk as well), VideoNULA and an external Pi second processor.
by jregel
Sun Mar 03, 2019 3:25 pm
Forum: programming
Topic: Newbie 6502 assembly questions...
Replies: 25
Views: 1369

Re: Newbie 6502 assembly questions...

A few more quick questions as I continue my dive into assembler, primarily around doing things “correctly”… If I have the following code: 10 DIM PROG 100 20 SCREEN=&3000 30 P%=PROG 40 [ 50 LDA #0 60 STA SCREEN 70 RTS 80 ] 90 CALL PROG Firstly, as the DIM statement reserves 101 bytes, does it matter ...
by jregel
Wed Feb 27, 2019 2:10 pm
Forum: hardware
Topic: A blitter for the beeb?
Replies: 86
Views: 8888

Re: A blitter for the beeb?

Thanks Dominic I totally appreciate there is a huge amount of work involved, and would only want to encourage you that some of us are fascinated by what you’re doing. From what you’ve demoed so far, and your explanations around your approach, the Blitter definitely sounds like a “must-have” upgrade ...
by jregel
Mon Feb 25, 2019 1:49 pm
Forum: hardware
Topic: A blitter for the beeb?
Replies: 86
Views: 8888

Re: A blitter for the beeb?

Thanks Dominic. One of the reasons I’m interested in the Blitter (although it seems to be much more than that, so perhaps you need a better name :-)) is it offers the potential to remove some of the remaining limitations with the Beeb’s design. The VideoNULA has arguably solved the biggest graphical...
by jregel
Sun Feb 24, 2019 2:19 pm
Forum: hardware
Topic: A blitter for the beeb?
Replies: 86
Views: 8888

Re: A blitter for the beeb?

I've been re-reading through the Blitter thread and considering the possibilities. Firstly, I was wondering if there is any news of this exciting project? Secondly, my interest up until now has been primarily around the graphics features, but spent some time last night considering the sound capabili...
by jregel
Fri Feb 22, 2019 5:07 pm
Forum: programming
Topic: Newbie 6502 assembly questions...
Replies: 25
Views: 1369

Re: Newbie 6502 assembly questions...

One question I do have: If I run the code, then manually call the address of PROG% (as above), it works. If I put the "CALL PROG%" statement in the BASIC program, it errors with " at line 2160" which is the line containing the CALL statement. Please can someone shed some light on this? It's actuall...
by jregel
Fri Feb 22, 2019 1:17 pm
Forum: programming
Topic: Newbie 6502 assembly questions...
Replies: 25
Views: 1369

Re: Newbie 6502 assembly questions...

Thanks everyone for the words of wisdom! I'm taking Tricky's advice focussing on readability at this stage, so I'm just trying to get a good result, without trying to optimise it yet. I also like the idea of calling the BASIC routines when appropriate. A couple of evenings ago, I managed to draw a l...
by jregel
Tue Feb 19, 2019 12:59 pm
Forum: stardot.org.uk
Topic: List of Acorn/BBC related websites
Replies: 26
Views: 7977

Re: List of Acorn/BBC related websites

Thanks - list of sites updated.

Mods - do you think it would be of value to sticky this thread for new visitors?
by jregel
Tue Feb 19, 2019 10:37 am
Forum: stardot.org.uk
Topic: List of Acorn/BBC related websites
Replies: 26
Views: 7977

Re: List of Acorn/BBC related websites

Oops - hit reply instead of editing the original post.
by jregel
Mon Feb 18, 2019 9:29 am
Forum: programming
Topic: Addressable memory for the screen
Replies: 3
Views: 378

Re: Addressable memory for the screen

Thanks for the confirmation. I was musing whether something like the Super Nintendo SuperFX or Sega Megadrive SVP approach would have been possible on a Master cartridge: On those consoles, some cartridges contained an extra custom RISC or DSP processor with local RAM which was used for running loca...
by jregel
Sun Feb 17, 2019 10:41 pm
Forum: programming
Topic: Addressable memory for the screen
Replies: 3
Views: 378

Addressable memory for the screen

I think the answer to this is "no", but is it possible for the 6845 to address sideways RAM as screen memory?

The reading I've done suggests that attempts to read > &7FFF will wrap around. I'm assuming that there is no workaround (even at the expense of losing hardware scrolling etc.)?

Thanks.