Bit of fun - One change only

on-topic Acorn-related news and discussions not covered by the other forums
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Rich Talbot-Watkins
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Re: Bit of fun - One change only

Post by Rich Talbot-Watkins » Mon Jan 07, 2019 3:45 pm

Always seemed to me that the Beeb's screen modes were unusually big. I once had the idea that, if you capped the max screen size to 16k (to give 25 line screen modes, which was pretty much the standard size on other 8-bit platforms), you could fit the screen nicely in a sideways RAM bank (or indeed two, for double buffering), and keep all of main RAM free for code. Maybe you could even reduce the cost by using 2MHz RAM and stall the CPU only when the video RAM were paged in.

This is a tricky game though, because I'd also want a proper 16 colour palette. From a games perspective, both getting extra colours and extra memory would've made a big difference.

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Re: Bit of fun - One change only

Post by Andrew_Waite » Mon Jan 07, 2019 7:55 pm

Rich Talbot-Watkins wrote:
Mon Jan 07, 2019 3:45 pm
you could fit the screen nicely in a sideways RAM bank (or indeed two, for double buffering), and keep all of main RAM free for code.
Only the part of the screen where action happens need be double buffered, whilst the part of the games screen used for the score, lives etc. can be left as single buffered. 20k of screen memory could be split in two, with 4k of the screen single buffered in main memory between &7000 and &8000, whist the remaining 16k between &8000 and &C000 double buffered using sideways RAM. This arrangement leaves ~28k below &7000 for code.
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Re: Bit of fun - One change only

Post by BigEd » Mon Jan 07, 2019 8:18 pm

BigEd wrote:
Sat Jan 05, 2019 4:59 pm
Here's an idea which is almost entirely cosmetic, but might have helped sales: change the OS ROM so the power-up screen has a nice colourful graphic. It's all very well to boot into a few lines of white text in mode 7, but it might not impress the punters.
I took the liberty of starting a new thread for this idea, and amongst other responses, dv8 came up with a very nice owl.
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Re: Bit of fun - One change only

Post by Rich Talbot-Watkins » Mon Jan 07, 2019 8:59 pm

Andrew_Waite wrote:
Mon Jan 07, 2019 7:55 pm
Rich Talbot-Watkins wrote:
Mon Jan 07, 2019 3:45 pm
you could fit the screen nicely in a sideways RAM bank (or indeed two, for double buffering), and keep all of main RAM free for code.
Only the part of the screen where action happens need be double buffered, whilst the part of the games screen used for the score, lives etc. need only be single buffered. 20k of screen memory could be split in two, with 4k of the screen in main memory between &7000 and &8000, whist the remaining 16k between &8000 and &C000 is double buffered using sideways RAM. This arrangement leaves ~28k below &7000 for code.
Yeah, but I was thinking in terms of hardware configuration too. It's easy to map &8000...&BFFF directly to the CRTC, with another CRTC line selecting the sideways RAM bank. (I think you could also abuse the CRTC address lines to be able to get an 8k wraparound screen, leaving a further 8k RAM free). I liked the idea of this configuration as it brought to mind the notion of separate video RAM, and just fitted into the existing memory map quite nicely. Giving the CRTC access to the top of main RAM plus sideways RAM would be a much more complex configuration, and it's also not clear how address wraparound would work in this case.

I don't think I ever worked on a game which used the entire screen (it was always reduced in size, both for memory reasons and to avoid needing to update so much each frame), so I wouldn't miss the big 20k screens.

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Re: Bit of fun - One change only

Post by Andrew_Waite » Tue Jan 08, 2019 4:15 pm

One thing I would have wanted is a copy of Elite for the Electron on a PLUS-1 cartridge.

The code would have run in the fast half of the Electron's memory map, and some of the things that were missing from the Electron version of the game, the Alien Items and Thargoids, could have been restored.
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Re: Bit of fun - One change only

Post by jregel » Sun Feb 03, 2019 10:06 pm

I'll basically echo what some others have already said:

BBC B:

64K standard, the additional RAM being 20K shadow RAM and 12K for OS/filing system workspace, keeping everything at E00.

Electron

Same as the BBC B: 64K, comprising 20K shadow RAM and 12K OS/filing system workspace.

Or, alternatively:

"Half a Plus 1": One cartridge slot and a joystick port built in. Release games on cartridge, but make them run from Sideways ROM (not using it just as a ROM FS), leaving all the RAM free for screen and variable data, not program code. Imagine Elite or Exile booting instantly.

(I still prefer my original option of giving it 64K as it makes the base machine better for everyone, not just gamers).

BBC Master 128:

Minor update to the ULA to give 16 colours, matching the PC CGA standard. This would be useful for the Master 512, and also gives better colours than a simple "bright" bit (e.g., two shades of grey - would make for a nice mode 1 with black/white/dark-grey/light-grey). Would also give a noticeable graphical upgrade to the original BBC.
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Re: Bit of fun - One change only

Post by Coeus » Tue Feb 05, 2019 2:04 pm

So without the contraint about it being cheap, it would have to be shadow RAM.

As 16K would not be enough, my plan would be to make the bottom 1K of RAM common to both banks and then switch the whole of the next 31K between the two banks.

This would put OSHWM at &0400 on both I/O processor and tube processor so the distinction between language workspace and the main part of RAM for user programs becomes unimportant. It would also mean if you wanted to write something in assembler to run instead of a language in ROM you had a fixed starting address, just like CP/M, so there is no need to fiddle around with relocation. And, of course, it means loads of memory for that program or the current language.

In that scheme the OS stuff that is above &0700 would be in the same bank as the screen and so would all of the paged ROM workspace, i.e. screen grows down, ROM workspace grows up, so the only time you'd not be able to use a particular screen mode is if you have so many ROMs taking workspace that the top of that is higher than the bottom of the screen.

It would probably also be worth exchanging the VDU variables in page three with the NMI routine/extended vectors, i.e. have the NMI and extended vectors in page 3 which is not bank switched and the VDU variables in the same bank as the screen so the VDU driver only has to bank switch once on each call.
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Re: Bit of fun - One change only

Post by BigEd » Tue Feb 05, 2019 2:10 pm

I like it!

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Re: Bit of fun - One change only

Post by B3_B3_B3 » Fri Feb 15, 2019 12:47 pm

Coeus wrote:
Tue Feb 05, 2019 2:04 pm
....shadow RAM....my plan would be to make the bottom 1K of RAM common to both banks and then switch the whole of the next 31K between the two banks.

This would put OSHWM at &0400 on both I/O processor and tube processor so the distinction between language workspace and the main part of RAM for user programs becomes unimportant. ......
In that scheme the OS stuff that is above &0700 would be in the same bank as the screen and so would all of the paged ROM workspace, i.e. screen grows down, ROM workspace grows up, so the only time you'd not be able to use a particular screen mode is if you have so many ROMs taking workspace that the top of that is higher than the bottom of the screen.

It would probably also be worth exchanging the VDU variables in page three with the NMI routine/extended vectors, i.e. have the NMI and extended vectors in page 3 which is not bank switched and the VDU variables in the same bank as the screen so the VDU driver only has to bank switch once on each call.
That seems even neater than the Master/B+ method
If only they had done that on the elk and simultaneously B+ (then Master which, as below, I would have preferred as an extended B+):

On top of this my one change would be for the B+ and Master to have remained compatible: I don't see much was gained from introducing the Masters incompatibility, plus the B+ was so short lived I suspect its owners felt rather agrieved when the incompatible Master appeared....

NB On an Elk with shadow RAM presumably modes 3 and 6 would be redundant, and could just use mode 0 and 4, perhaps simplifying ULA?
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Re: Bit of fun - One change only

Post by B3_B3_B3 » Wed Feb 27, 2019 8:45 pm

A little one:
The electron could have tried a bit harder with mode 6 variant standing in for mode7:

1) Surely, for little programming/ROM space cost, chars above 127 could have just been spaces rather than filling screen with squiqqles fot teletext graphics/control chars etc?

2) Monochrome software emulation of mode 7 in mode 6?

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Re: Bit of fun - One change only

Post by B3_B3_B3 » Thu Apr 04, 2019 8:19 pm

The BBC User guide could have introduced some simple 6502 assembly in the same friendly reassuring (non-scary?) way as the Atom manual rather than just saying thats a subject for a different book (which is more offputting)?

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Re: Bit of fun - One change only

Post by Commie_User » Sun Apr 14, 2019 11:07 am

I suppose you can say anything. Had Acorn not decided to sell the BBC 128 base unit alone for a monster £500 in 1985, they could have extended the BBC's life force?

Would any of these changes have actually rescued Acorn or extended any dominance?

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Re: Bit of fun - One change only

Post by Andrew_Waite » Sun Apr 14, 2019 3:53 pm

Commie_User wrote:
Sun Apr 14, 2019 11:07 am
I suppose you can say anything. Had Acorn not decided to sell the BBC 128 base unit alone for a monster £500 in 1985, they could have extended the BBC's life force?

Would any of these changes have actually rescued Acorn or extended any dominance?
8-bit technology was pretty long in the tooth by 1985, 1984 having seen the 68k based Apple Mac and Sinclair QL. 1985 saw Acorn's 32-bit ARM development system which became the dominant technology of modern mobile computing.
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Re: Bit of fun - One change only

Post by B3_B3_B3 » Wed Apr 17, 2019 7:44 pm

For the original BBC B:

Perhaps it would have made more sense for
1) the tube connector to be internal: making 2nd processors cheaper by not requiring a cheese box case with own PSU
2) bring the lines for extra sideways ram/rom to be brought out on an IDC connector(PCB male 'socket') in its place: allowing simple plug in ROM boxes/boards for expansion....?

Did Acorn plan to have a ROM IDC connector but run out of space?

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Re: Bit of fun - One change only

Post by Kazzie » Wed Apr 17, 2019 9:43 pm

B3_B3_B3 wrote:
Wed Apr 17, 2019 7:44 pm
For the original BBC B:

Perhaps it would have made more sense for
1) the tube connector to be internal: making 2nd processors cheaper by not requiring a cheese box case with own PSU
2) bring the lines for extra sideways ram/rom to be brought out on an IDC connector(PCB male 'socket') in its place: allowing simple plug in ROM boxes/boards for expansion....?

Did Acorn plan to have a ROM IDC connector but run out of space?
Some of those second processors used a lot of the space in the cheesebox, e.g. the 32016:
Image
And while putting the second processor inside the Beeb would remove the need for a second power supply, it would add to the load of the existing power supply. (Would they have known in advance the power requirements of their unreleased second processors?)

Pooh-poohing and pessimism aside, your suggestion of Acorn planning a ROM IDC connector is a very interesting one. I wonder how that interplays with their use of the five ROM slots at product launch (Basic in IC51, OS across four ROMs in ICs 52, 88, 100, and 101)...
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Re: Bit of fun - One change only

Post by Commie_User » Wed Apr 17, 2019 11:43 pm

Would those changes have pushed the prices up? Schools needed enough cash incentive to splash out on a BBC as it was.

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Re: Bit of fun - One change only

Post by AndyF » Thu Apr 18, 2019 9:14 am

Commie_User wrote:
Wed Apr 17, 2019 11:43 pm
Would those changes have pushed the prices up? Schools needed enough cash incentive to splash out on a BBC as it was.
I can just about (if I'm correct, I was not very old then!) some kind of fund raising to get a BBC in the first place at our primary, or perhaps it was some extra monies as I think the govt. paid a contribution towards ?

I can remember it was a tape based one obviously and the first disc drive appeared for it about a year or so after that, one of those huge (likely single sided 40 track affairs) double height units. I think there was some fund raising for that too.

Difficult to be sure as I was only about 6 or 7 at the time!
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Re: Bit of fun - One change only

Post by BigEd » Thu Apr 18, 2019 9:29 am

In a recently posted PDF, in an interview with Kenneth Baker, it was said that the government would pay half the price of one computer if schools could pay the rest - so long as they didn't already have one:
"It is a very successful scheme and I am very proud of that. Slightly more than 3,000 secondary schools did not have microcomputers and we have already helped 2,000 of them ̶ a great success story".

Under the scheme, the Government promises to pay half the cost of either a Research Machines 380-Z or a BBC Microcomputer for any school which does not already have any microcomputers. The other half of the cost has to be met by the school, the Local Education Authority or by parent/teacher associations. As from January 1, 1982 the scheme is being extended to those schools which already have some equipment.

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Re: Bit of fun - One change only

Post by Commie_User » Thu Apr 18, 2019 10:09 am

Well it all looks like it worked out as well as it was ever going to. Though I notice nobody wanted the change which Your Computer wanted in 1982 - for BBC Television to commit ratings suicide and have The Computer Programme use micros as scientific aversion therapy.

Well played sirs. Very well played! =D>
TEACHERS must be very disappointed by the BBC's Computer Programme series, which
began transmissions to schools on January 11. First, most of the schools which had been
promised priority delivery of a BBC Microcomputer in time for the start of the series are
still waiting for their computers to be made ̶ largely because of reliability problems with
some of the chips. Secondly, those schools which were supplied in time for the start of the
series would have found that they do not need it. The BBC Microcomputer might well be
the best value for money to have hit the market for some time but it simply does not seem
very relevant to the Computer Programme, which treats computing in general and
abstract terms. The BBC's argument is that it is unreasonable to expect all the viewers to
follow the series through from start to finish and that there is, therefore, no point in trying
to teach the viewers much about programming other than to Load and to Run programs
from cassette.

The BBC series is still interesting and will no doubt help the complete novice to
understand microcomputers and the kind of programs that one can expect them to run.
Those teachers who were planning to let their pupils view the entire series during the
school day might well, however, have some doubts about spending so much of their
valuable time on such a general overview of the subject. We are sure that most would have
welcomed a more detailed and informative look and an attempt to teach some of the
specifics of the subject. Why is it that television is terrified of going into detail?
The problems that the BBC' has had in making its series raise a more general point
about the problems that the media have always had in dealing with science, especially in
programmes which are supposed to be educational. With the exception of BBC Radio's
science programmes, the emphasis has always been on being entertaining to the exclusion
of detail. We suspect that one of the reasons that the BBC abandoned its attempts to teach
us how to program the BBC Microcomputer is that no way could be found of fitting hard
detail into the received view of how a sleek and glossy science program should look and be
presented. Television science programs are always produced and presented by generalise
who do not have a science background. These generalists then turn to scientists to advise
them on the content; accepting and rejecting that advice is the prerogative of the
programme makers. We would prefer an approach in which the programmes were
produced and presented by scientists who could accept and reject the programme-making
advice of the generalists.
#-o :lol:

http://www.retro8bitcomputers.co.uk/Con ... 982_02.pdf

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Re: Bit of fun - One change only

Post by AndyF » Thu Apr 18, 2019 11:41 am

BigEd wrote:
Thu Apr 18, 2019 9:29 am
In a recently posted PDF, in an interview with Kenneth Baker, it was said that the government would pay half the price of one computer if schools could pay the rest - so long as they didn't already have one:
I do recall our Primary's was our first machine, I can remember well the wheeled trolley it lived on! That was a bit fun as the site was two stories. As previous given my age I can't really remember a great deal more. Was an exiting time though I think one of the first erm 'games' i saw on it and played was Flags. :)

^ Only problem here is I suspect Flags was not that old, so it may be my memory playing tricks or we had Flags after we had a disc drive, I can't be sure. Best guess is the drive arrived possibly say nine to twelve months or so after the machine itself, maybe a bit more.
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Re: Bit of fun - One change only

Post by 1024MAK » Thu Apr 18, 2019 2:08 pm

This thread has gone rather off topic.

When I get time, unless there are any objections, I’ll split the discussion about computers in schools into it’s own thread.

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Re: Bit of fun - One change only

Post by AndyF » Thu Apr 18, 2019 5:19 pm

1024MAK wrote:
Thu Apr 18, 2019 2:08 pm
This thread has gone rather off topic.

When I get time, unless there are any objections, I’ll split the discussion about computers in schools into it’s own thread.

Mark
Please. :)

I'm quite guilty it seems too even though the original "one change only" , I was the topic starter :oops:
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Re: Bit of fun - One change only

Post by B3_B3_B3 » Thu Apr 18, 2019 8:10 pm

Kazzie wrote:
Wed Apr 17, 2019 9:43 pm
....
Some of those second processors used a lot of the space in the cheesebox, e.g. the 32016...
1) So, I suppose for those you would need to bring a ribbon outside (just like for a RomBox)...so perhaps the internal IDC could be placed near the left case edge>

2) On further thought about "Did Acorn plan to have a ROM IDC connector but run out of space":
they didn't add one to the B+ or Master so perhaps not (though perhaps by Master they felt sideways RAM would take over plus it had lots of built in ROM software anyway?).
But given they built in support for 16 sideways ROMs from the start it seems strange to have no official expansion mount/method planned .....
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Re: Bit of fun - One change only

Post by B3_B3_B3 » Mon Apr 29, 2019 7:32 pm

Was the analog port worth the extra cost?

1 It forces the choice of ADC, most people probably never used it etc etc

2 A digital user port is easier protected by optical isolators.

3 Attaching the chosen ADC to user port and waggling the lines surely teaches more (line waggling code could be provided for those who want)

4 Joysticks could go on the user port, cheaper std Atari ones .

5 Perhaps a 2nd (via free?) User port more useful or just use printer port?

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Re: Bit of fun - One change only

Post by 1024MAK » Mon Apr 29, 2019 10:04 pm

The easiest way to answer is to ask another question: What other 8 bit home micro came with a built in analogue port?

Of course, you also need to check the specifications required by the BBC...

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Re: Bit of fun - One change only

Post by helpful » Tue Apr 30, 2019 2:50 am

Analogue joysticks FTW! So much better than those tacky digital things on inferior computers :D

More seriously, I suspect the analogue port got a lot of use in school (and commercial?) science labs for hooking up to monitoring equipment.
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Re: Bit of fun - One change only

Post by AndyF » Tue Apr 30, 2019 9:47 am

I think with the B opposed to the A at least, it was a trying perhaps to be a case of "all things to all men" (not sexist, just a phrase) :)

I did actually sort of agree with the Atari type 9pin stick socket but then again I'd guess there was some kind of (Watford perhaps?) 'adaptor' to permit said 9pins to work in the analogue socket to some degree at least, maybe ?

Regarding the other uses of the socket, as far as I can recall at least in all three skools (typo intended) I attended no use was ever made of anything other than the regular RBG/Tape/Disc/Network/Tube ports etc. Exception here I do recall the PS on the rebuilt network used parallel instead of serial for its Epson LX of some description.

Mind you I think the situation would of been much different in perhaps more erm 'affluent' area's where they had spent a few more pennies in the education system perhaps but that's something for both another time and probably another forum!
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Re: Bit of fun - One change only

Post by B3_B3_B3 » Tue Apr 30, 2019 9:05 pm

helpful wrote:
Tue Apr 30, 2019 2:50 am
Analogue joysticks FTW! So much better than those tacky digital things on inferior computers :D
Hmm, I found mine (a voltmace) a bit disappointing for most games. A digital joystick port might have meant joy pads for the BBC... :) (I like joypads....)
helpful wrote:
Tue Apr 30, 2019 2:50 am
More seriously, I suspect the analogue port got a lot of use in school (and commercial?) science labs for hooking up to monitoring equipment.
But my point is if its separate the expensive computer itself is more easily protected from electrical mishaps and a broken ADC unit can be swapped out quickly (and perhaps repaired elsewhere). Also, there is a choice of ADCtype possible...

I don't remember any other computers with ADCs (other than Apple iis cheapo paddle inputs?)

Could the BBC not have been persuaded an external ADC was better, they were persuaded to accept the 6502?
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Re: Bit of fun - One change only

Post by 1024MAK » Tue Apr 30, 2019 9:29 pm

As far as I can remember, the BBC Micro was the only 8 bit machine with a true analogue port. As in it used a proper ADC chip.

Other 8 bit computers used either digital joystick ports, paddle inputs where relatively simple circuitry used the resistance of the paddle to form part of a monostable timer or ‘analogue’ joystick ports that did the same thing (PC joystick ports).

The ADC chip in the model B was in a socket, so if it was damaged, it was relatively easy to change.

Could it have been left out? Yes, of course. Did many people use the analogue port (other than using it for joysticks), no. But then, most model B’s had most of their ports left unused most of the time...

If you wanted a machine without all those ports, then the model A or the Electron were available.

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Re: Bit of fun - One change only

Post by B3_B3_B3 » Thu May 02, 2019 6:57 pm

Rich Talbot-Watkins wrote:
Mon Jan 07, 2019 3:45 pm
Always seemed to me that the Beeb's screen modes were unusually big. I once had the idea that, if you capped the max screen size to 16k (to give 25 line screen modes, which was pretty much the standard size on other 8-bit platforms), you could fit the screen nicely in a sideways RAM bank (or indeed two, for double buffering), and keep all of main RAM free for code. Maybe you could even reduce the cost by using 2MHz RAM and stall the CPU only when the video RAM were paged in......
Would 16K max for screen bitmaps mean the other 16Ks (8 of 16 by 1bit chips) could be 8 slower access == cheaper ones?

Is the a reason why there were no 3 bit colour modes (eg a 12 K 8 colour 160 * 256 or 200 mode 2-ish ) minus the not very useful flashing colours:
was it because the 6845 was byte based because it was originally for text displays?

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