Search found 114 matches

by philb
Thu Nov 09, 2017 9:38 pm
Forum: hardware
Topic: Another A5000 restoration....
Replies: 10
Views: 373

Re: Another A5000 restoration....

Some things to look at, perhaps: If the IDE adapter activity LED is stuck on then that might mean it is seeing itself permanently selected. Check pin 37 of PL9 which should be high except when the IDE space is being read or written. You might try reading or writing the registers in IDE space directl...
by philb
Wed Nov 08, 2017 9:21 am
Forum: hardware
Topic: Arduino Filestore
Replies: 36
Views: 1185

Re: Arduino Filestore

That assumes that, without the 6854, you have some alternative form of serialise/deserialise logic (with at least a couple of bytes of FIFO) so that you can operate byte by byte rather than bit by bit. That's exactly what I have in mind (using a small CPLD to handle clocking bits onto and off the w...
by philb
Tue Nov 07, 2017 7:58 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

It does seem to work rather better with an external PSU connected to the scsi2sd and a different SCSI cable. I don't seem to be able to get it to respond to anything other than SCSI ID 0, so I wasn't immediately able to get it running at the same time as my old hard disk, but I guess I can swap the ...
by philb
Mon Nov 06, 2017 9:58 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

OK, makes sense. The scsi2sd manual does say that man can live on TERMPWR alone, but it's a bit vague about how much exactly it needs. If the other SCSI cable doesn't help then I'll try again tomorrow with a better PSU. I guess I should also configure the MDFS for serial printing (or buy a parallel ...
by philb
Mon Nov 06, 2017 8:47 pm
Forum: hardware
Topic: Another A5000 restoration....
Replies: 10
Views: 373

Re: Another A5000 restoration....

Does RISC OS 3.1 even check for the floppy hardware before registering the drive? I thought it was only based on the *Configure Floppies setting. But equally I would have expected a delete-power-on to reset that to 1, so I guess there must be a bit more going on than that.
by philb
Mon Nov 06, 2017 8:31 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

So, the only external SCSI box that I could immediately find for my scsi2sd (and that I have cables for) is even more ludicrous than Daniel's... https://lh3.googleusercontent.com/UeGxutwkfZ9Gtw6p7r9Wcg0vIpHoualK553K1zFHxXtSnj3x2T9c3MJRc_SqoMC062fTBtZ0M022Jc2L8VY13TPwshRYS-tyFcKCoqNjnu2qlD3gbef31e2fE...
by philb
Sat Nov 04, 2017 10:51 pm
Forum: hardware
Topic: Issue 1 BBC, how to tell ?
Replies: 12
Views: 277

Re: Issue 1 BBC, how to tell ?

I believe the first production release of the BBC B was the Issue 2 board.... Acorn used to have a convention that prototype boards had letters (Issue A etc) with Issue 1 always being the first production version, and I'm reasonably sure this was the case when the Beeb was first launched. But I thi...
by philb
Sat Nov 04, 2017 6:02 pm
Forum: hardware
Topic: Unix on the Beeb
Replies: 36
Views: 1015

Re: Unix on the Beeb

Having Unix on the PDP-11 copro would be brilliant but would involve a bit of work. Yeah. It'd be quite a fun project, but the current PDP11 copro (at least the LX9Co one, which is the only one I have any hardware for :D ) doesn't have an MMU either. So I suppose the first order of business would b...
by philb
Fri Nov 03, 2017 10:24 pm
Forum: hardware
Topic: Unix on the Beeb
Replies: 36
Views: 1015

Re: Unix on the Beeb

Does v7 run natively on the PDP-11 copro? Seems like cutting SIMH out of the equation would be the way to success :D

But of course, what you really want to do is build a Unix kernel that executes on the 6502 directly. DId v7 require an MMU?
by philb
Tue Oct 31, 2017 8:44 pm
Forum: hardware
Topic: RPC loses power
Replies: 3
Views: 113

Re: RPC loses power

If you mean it shuts down altogether, that isn't likely to be the battery. It is more likely to be the power supply. I've never seen a RiscPC power supply though so I have no idea what they are like. Shutting down after a few minutes and then working after a rest sounds like overheating perhaps. Doe...
by philb
Sat Oct 28, 2017 8:35 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

Ah yes, right. Ludicrous but authentic!

I wonder how the textured finish on the upper case is done. Special paint I suppose.
by philb
Sat Oct 28, 2017 6:18 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

Found it! As I suspected, two SCSI2SDs and two IDE-to-SD adapters. It seems I had put them in an unmarked box on a shelf in the hardware lab. Now I just need to find a working floppy drive to boot from, a SCSI cable, and I'm all set. It's quite tempting to get a new drive box made up for my SCSI2SD ...
by philb
Sat Oct 28, 2017 4:04 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

This is a bit irritating because that IC is all tangled up in the SCSI/2 mod (it has pins cut, other pins bridged, and components soldered onto the back side of the board) so it will be a bit of a pain to replace. But I do have a spare and I will have a go at it on Monday if nothing else gets in th...
by philb
Fri Oct 27, 2017 10:13 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

Yeah, absent test equipment I don't think there's much you can really do to debug this sort of failure. If you wanted to send the board to me then I'd be happy enough to have a look at it.
by philb
Thu Oct 26, 2017 9:16 pm
Forum: hardware
Topic: SJ disk format documented?
Replies: 2
Views: 112

Re: SJ disk format documented?

Thanks, that's what I was looking for.

The directory format does seem to broadly match what I have but the block numbers in the directory entries seem to be all wrong. I think possibly my disk image has ended up with the logical blocks in slightly the wrong order, some further sleuthing required.
by philb
Thu Oct 26, 2017 7:24 pm
Forum: hardware
Topic: SJ disk format documented?
Replies: 2
Views: 112

SJ disk format documented?

I had another go at imaging my HDFS hard disk this afternoon. Yesterday it was sticking at track 26 but giving the head positioner a bit of a shove with the end of a screwdriver at the appropriate moment seems to have sorted that out, and I now have pretty much all the sectors recovered. So, obvious...
by philb
Wed Oct 25, 2017 8:34 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

Oh, right, good work. I'm not sure Steve was all that involved with the MDFS though, I think that was before his time at SJ. I think transputers and ATM were more his thing. On a related tangent, this evening I managed to read at least some of the data off my old HDFS hard disk. I think I now have a...
by philb
Mon Oct 23, 2017 10:39 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

I think the ROM monitor does talk to the serial port but the way in which the monitor is entered is a bit inscrutable (to me). I'm fairly sure that in a stock ROM you can't get there until you've passed the hardware diagnostics, but obviously it wouldn't be very hard to make a version that bypassed ...
by philb
Mon Oct 23, 2017 10:21 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

I also see from the disassembly that SRL's Portable Monitor features in the ROM. I'm not quite sure how you invoke that though. I assume you talk to it through the serial port, and if it were possible to get the monitor running then this might give you a further route to debugging.
by philb
Mon Oct 23, 2017 7:39 pm
Forum: hardware
Topic: A5000 IDE interface just died... what to try next?
Replies: 19
Views: 723

Re: A5000 IDE interface just died... what to try next?

...but if you can't get floppy to work either, then the fault is possibly a dead controller and you can't get replacements of these :( (...even if you could, they are very fine pitch smd, so would need some serious expertise to replace) There seems to be a guy on ebay selling 82C711s at the moment....
by philb
Mon Oct 23, 2017 2:21 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

Here's the order of the checks it does, based on JGH's ROM disassembly: 1. ROM (7 flashes) 2. SIO (3 flashes) 3. FDC (4 flashes) 4.. SCSI (6 flashes) 5. CTC (5 flashes) 6. RAM (2 flashes) The RAM test involves writing to banked memory and if the address lines or page control were not working correct...
by philb
Mon Oct 23, 2017 11:54 am
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

At what point does it do that? All lights come on, and then power & no clock stay on and the system LED starts flashing. Does that mean that by that point it has copied the ROM to RAM and is executing it? Yes. In what circumstances (if ever) would you get a RAM fault indicated? It does a more t...
by philb
Sun Oct 22, 2017 9:07 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

one minor thing - sometimes only no clock and power lights come on, but immediately switching it off and on again gets it going. Mine does that as well sometimes and the problem seems to be that the RESET generator circuit R49/C14 isn't working properly so the system gets stuck in reset. Sometimes ...
by philb
Sun Oct 22, 2017 8:08 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 216
Views: 9026

Re: Dead MDFS Resurrection

I think Daniel had a self-built test ROM at one point but I don't know exactly what it did. What exactly are the symptoms of your unit at the moment, is it doing the "stuck with all LEDs on" thing? The way I identified the bad RAM on mine was to reboot it repeatedly (putting a squarewave a...
by philb
Sat Oct 21, 2017 8:18 pm
Forum: hardware
Topic: Broken MDFS
Replies: 30
Views: 975

Re: Broken MDFS

I guess I need to capture all the signals around IC43 and see if that part appears defective. I spent another half-hour in the lab today and it does seem that this chip is the culprit. Pins 10 and 11 are high, pin 9 pulses low in the same way as IC62 pin 12, but pins 5 and 12 are stuck high and low...
by philb
Sat Oct 21, 2017 8:07 pm
Forum: hardware
Topic: ST506 HDD woes
Replies: 37
Views: 1568

Re: ST506 HDD woes

It's odd that your drive's giving a "no index" error code, given that it's not even managing to spin the platter. You'd have thought it would give one of the motor errors in preference, as this is the more fundamental problem. I think that's exactly what "no index" means. The IN...
by philb
Tue Oct 17, 2017 10:19 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2474

Re: RISC-PC Not Working

If you moved the wires around a bit then that would probably have been enough to disturb the parasitic capacitances and change the frequency that the RTC counts at. 10pF isn't much!
by philb
Tue Oct 17, 2017 10:13 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2474

Re: RISC-PC Not Working

Jolly good. It sounds like you figured it out already, but the answer to your previous question is that the +ve end of the diode is the one away from the stripe. If your RTC is gaining time then that would suggest you don't have enough load capacitance on the crystal. You could try adding some small...
by philb
Mon Oct 16, 2017 7:37 pm
Forum: hardware
Topic: Fileserver reverse engineering
Replies: 0
Views: 129

Fileserver reverse engineering

Following the awesome work that was done to trace the MDFS circuit ( http://stardot.org.uk/forums/viewtopic.php?f=3&t=9407&p=182600 ) I was left wondering whether anybody had ever done this for the somewhat rarer FDFS and HDFS. Anyone know of any efforts in that direction? It'd be quite plea...
by philb
Mon Oct 16, 2017 6:50 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2474

Re: RISC-PC Not Working

No resistor, is that vital? What value should I use? They are 2150mAh (mAH? MaH? MAH? Mah?) batteries. It's fairly vital to restrict the charging current into the battery, yes. Otherwise the batteries will overheat and may start venting. The fact that you currently have a diode in series will be he...

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