Acorn A3000 Address exception on boot

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
RoryMakarov
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Acorn A3000 Address exception on boot

Postby RoryMakarov » Thu Sep 07, 2017 12:08 am

So I dug my old A3000 out and tried to turn it on, but it's giving this error on bootup:

Error: Address Exception at &20 (Error Number: &80000003)

Holding down R and DELETE give the same error, but if I do a Shift+Break I get "RISC OS 2048K", so I guess it is reading the ROMs?

Tomorrow I'll open it up and see the state of the battery etc, until then does anyone know what the error code means and what the problem may be?

philb
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Re: Acorn A3000 Address exception on boot

Postby philb » Thu Sep 07, 2017 6:37 am

"Address exception" means that the software tried to access a nonexistent memory address. Registers on the ARM2 are 32 bits wide but the address space is only 26 bits. Any attempt to use a value with one of the high 6 bits set as an address will cause an address exception. In your case the offending address seems to have the top bit set.

Is this RISC OS 2 or RISC OS 3? Do you have a memory expansion card in the machine? If so, take it out and try again.

RoryMakarov
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Re: Acorn A3000 Address exception on boot

Postby RoryMakarov » Thu Sep 07, 2017 11:14 am

I honestly can't remember what RISC OS it had, the ROMs have 1992 on them however. It has a MIDI Expansion, and what looks to be a 1meg expansion card by 'Cumana Ltd' above the memory, the battery had corroded so I've taken it out. Would the best bet be to start by disconnecting out the Cumana card or the MIDI expansion?

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danielj
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Re: Acorn A3000 Address exception on boot

Postby danielj » Thu Sep 07, 2017 11:16 am

Goodness, you're lucky that's still working! First thing. Get everything out, get the motherboard out. The corroded bits, wash them over with distilled (i.e. white) malt vinegar and give it a bit of a gentle rub with an old toothbrush. Rinse it well with water, then, if you're in a hard water area, give it a good rinse with distilled water and let it dry off!

d.

philb
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Re: Acorn A3000 Address exception on boot

Postby philb » Thu Sep 07, 2017 11:25 am

That looks like RISC OS 3. I think the RISC OS 2 ROMs didn't occupy the full width of the sockets. The reason I asked is that RISC OS 3 has a more extensive POST and if it gets as far as showing you a prompt then I guess the POST must not be detecting any errors.

The MIDI card is unlikely to be a problem, it is isolated from the main processor bus by a load of latches. The 1MB expansion is a more likely culprit. But I would probably pull both out to begin with and, as Daniel says, give the board a good wash down.

RoryMakarov
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Re: Acorn A3000 Address exception on boot

Postby RoryMakarov » Thu Sep 07, 2017 11:36 am

Okay cheers I'll get to work cleaning the motherboard. I have some Isopropyl alcohol 91% will that work, or am I best with the vinegar? How long should I leave it to dry after?

philb
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Re: Acorn A3000 Address exception on boot

Postby philb » Thu Sep 07, 2017 11:44 am

The reason for using vinegar is to neutralise any alkaline residue from the battery leakage. IPA won't do that. You could probably use IPA as a final rinse to get rid of the vinegar, but clean water will work just as well and might actually do a better job at removing some of the contamination.

I would leave it to dry at least overnight to give any water trapped under ICs and in similar places a chance to evaporate.

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danielj
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Re: Acorn A3000 Address exception on boot

Postby danielj » Thu Sep 07, 2017 11:46 am

Indeed, a bit of IPA in the final rinse can help the water evaporate marginally faster, but there's really no need to use it. Getting rid of salty chemicals, water's always best :). Give it 24 hours in a warm place to dry off, 48 if you're feeling nervous :)

d.

RoryMakarov
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Re: Acorn A3000 Address exception on boot

Postby RoryMakarov » Sat Sep 09, 2017 6:04 pm

Thanks for everyone's advice, removing the memory expansion seems to have fixed it. It now seems to boot up to the desktop. I say seems to as I can only see a very faint outline amongst a grey screen on my monitor. I'm using a SCART adapter which when I last used it many years ago worked but on an old CRT TV, now I only have modern flat screens and a SCART to HDMI converter box (which works for my BBC B) so either the output isn't compatible or something got damaged. I'm wondering if I should get this http://www.ebay.co.uk/itm/Archimedes-A3000-etc-Video-convertor-SVGA-output-with-cable-for-LCDs-etc-/181817436882?hash=item2a5529ead2:g:260AAOSwPcVVuLkK?

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1024MAK
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Re: Acorn A3000 Address exception on boot

Postby 1024MAK » Mon Sep 11, 2017 8:22 am

That SCART lead is a RGB type. But it does not have any control signal connections to tell the display device to automatically switch to RGB mode. So if your equipment has manual user controls, see if you can use them to select RGB AV mode.

Also the A3000 has to be set to a display mode that outputs at normal TV picture frequencies (15625 Hz horizontal, 50 Hz vertical for 625 lines interlaced video).

Can you solder?

I would not jump the gun and buy the item in the eBay link.

Mark
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RoryMakarov
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Re: Acorn A3000 Address exception on boot

Postby RoryMakarov » Mon Sep 11, 2017 10:52 am

Yes I can solder. I've heard on this forum of people getting these to work with BenQ monitors, do Acorn output to VGA cables exist? I suppose another options would just be to buy a small CRT TV from somewhere.

philb
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Re: Acorn A3000 Address exception on boot

Postby philb » Mon Sep 11, 2017 11:32 am

RoryMakarov wrote:Yes I can solder. I've heard on this forum of people getting these to work with BenQ monitors, do Acorn output to VGA cables exist?


Yes, I think the Welcome Guide has details of the pinout, or it's certainly on the web. I'm not sure if you can buy them off the shelf anywhere anymore. Note though that most modern VGA monitors can't scan the TV-resolution modes that an A3000 would most naturally use and that the A3000 can't generate the right dot clock frequencies to produce accurate VESA timings. It will output 640x480 after a fashion but I'm not sure how good the compatibility with either monitors or software will be. Also, the increased video DMA bandwidth requirement causes a noticeable hit to CPU performance on an uncached ARM2.

I suppose another options would just be to buy a small CRT TV from somewhere.


That might be a better option. It doesn't even necessarily have to be a CRT, a cheap LCD TV would probably be fine as well. Anything that is sold as a TV (rather than a monitor) can almost certainly accept 576i video and do the scan conversion internally. Of course, finding a small/cheap LCD TV with suitable inputs might be a little bit of a challenge.

BradBrad
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Re: Acorn A3000 Address exception on boot

Postby BradBrad » Sun Sep 17, 2017 12:16 am

If it helps, I made a cheap scart cable from info here:

viewtopic.php?t=3750

It works well but I probably have to change a jumper or something as the whole picture is shifted to the right a bit on my lcd tv when compared to composite video out.


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