A540 (or R260) 4MB card

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IanS
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A540 (or R260) 4MB card

Post by IanS » Sat May 02, 2020 12:13 pm

Following on from the post on the "Today I received" thread I made an A540 4MB card. (viewtopic.php?p=267419#p267419 )
IMG_20200501_200238.jpg
IMG_20200501_200249.jpg
IMG_20200501_200150.jpg
It's lego hardware design. I checked the wiring of a 4MB simm from the ifel A3000 adapter - http://chrisacorns.computinghistory.org ... 4K4MB.html along with the circuit diagram from the A540 TRM - http://chrisacorns.computinghistory.org ... awings.zip. Combined the two and made a PCB.

In the process I managed to swap the power pins on the MEMC, thus the wire bodges on the back of the card (only kiled one MEMC before I noticed). And the SIMM PCB footprint was a vertical socket, so I modified it to make it right-angle, and pushed it over the wrong way, so pin 1 is at the wrong end.

The MEMC was bought from Ifel on ebay some time ago. The Simm was donated by Zarchos at the last Abug.
OE.png
The OE pin on the SIMM chips ii tied to GND, so I had to lift the pin from each chip and wire it up to the output of the inverter (via the resistor). It obviously works ok without this in an A3000, but with multiple MEMC's if gives a RED screen at power-on.

I may have a go at a new PCB layout and get some hot-air gear and transfer the chips from a SIMM (I have lots, thanks Zarchos)
Last edited by IanS on Sat May 23, 2020 5:00 pm, edited 2 times in total.

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Re: A540 (or R260) 4MB card

Post by steve3000 » Sat May 02, 2020 2:33 pm

So from your other post, you say it works with a mix of original 4mb cards to get 16mb? That's great to see! As there has always been talk about possible issues with A540s using a mix of different RAM cards with un-matched MEMCs, to get 16mb.

Do you plan to make any more cards, or release the design?

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Re: A540 (or R260) 4MB card

Post by IanS » Sat May 02, 2020 3:16 pm

steve3000 wrote:
Sat May 02, 2020 2:33 pm
So from your other post, you say it works with a mix of original 4mb cards to get 16mb? That's great to see! As there has always been talk about possible issues with A540s using a mix of different RAM cards with un-matched MEMCs, to get 16mb.

Do you plan to make any more cards, or release the design?
There definately was a tech note from Acorn about timing parameters with multiple MEMCs. Steve Picton remembers seeing it, but can't find a copy. The MEMC chips in my Simtec cards have a hand written value (like "18.0") on them, which I always assumed was the result of testing.

The design is effectively just the Acorn board with different chips.

I will probably do a small batch when I try swapping chips from the simms onto a new PCB. The sim socket I have is bit too wide, so more than one in a machine would be a difficult fit.

Would anyone be interested if I made some, what would you be prepared to pay?

edit: I was reading it upside down. The value written on the chip is 18.0
Last edited by IanS on Mon Jun 01, 2020 11:03 pm, edited 1 time in total.

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Re: A540 (or R260) 4MB card

Post by RobC » Sat May 02, 2020 3:38 pm

IanS wrote:
Sat May 02, 2020 3:16 pm
Would anyone be interested if I made some, what would you be prepared to pay?
I'd be interested in a few for my A540 and R260 - my existing cards are a bit flaky so I have MEMCs. What speed RAM are you thinking of fitting?

They are pretty hard to get hold of so I'd be happy to pay a reasonable amount.

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Re: A540 (or R260) 4MB card

Post by IanS » Sat May 02, 2020 3:45 pm

RobC wrote:
Sat May 02, 2020 3:38 pm
IanS wrote:
Sat May 02, 2020 3:16 pm
Would anyone be interested if I made some, what would you be prepared to pay?
I'd be interested in a few for my A540 and R260 - my existing cards are a bit flaky so I have MEMCs. What speed RAM are you thinking of fitting?

They are pretty hard to get hold of so I'd be happy to pay a reasonable amount.
How do you know it isn't the MEMCs that are flaky?? :) (Whose cards do you have as the Acorn cards had soldered MEMCs?)
The SIMMs I have for chip salvage have 50nS parts on them.
My resonable may not match your reasonable.

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Re: A540 (or R260) 4MB card

Post by RobC » Sat May 02, 2020 4:29 pm

IanS wrote:
Sat May 02, 2020 3:45 pm
How do you know it isn't the MEMCs that are flaky?? :) (Whose cards do you have as the Acorn cards had soldered MEMCs?)
Because they all work in my in my A440/1. Not sure who they were made by - I can dig them out if you want. I have a couple of working Acorn cards too.
IanS wrote:
Sat May 02, 2020 3:45 pm
The SIMMs I have for chip salvage have 50nS parts on them.
That's fast enough for me :-)
IanS wrote:
Sat May 02, 2020 3:45 pm
My resonable may not match your reasonable.
True - I could have phrased it better and said "considerable". How much is your reasonable? :D

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Re: A540 (or R260) 4MB card

Post by steve3000 » Sun May 03, 2020 2:03 am

I’d be interested in one card. :)

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Re: A540 (or R260) 4MB card

Post by IanS » Wed May 06, 2020 5:13 pm

Time to show my ignorance.

I'm doing a new PCB layout which uses the chips from the SIMMs rather than the SIMM in a socket. Perviously I kept everything matched with a one-to-one mapping (almost, we'll get to that later).

To make the layout easier I'm working on the assumption that I can re-order the Ra<X> signals from the MEMC to the RAM chips without a problem. I can also re-order the data bits within each byte as long as all the bits for a byte go to the same byte on a RAM chip with the associated Cas signal. (I swapped byte 1 and 2 and Cas1 and 2 on the original board without issue)
But I do have to keep the A<x> signals from the connector to the MEMC in the right order so the MEMC can be configured correctly by RISC OS.
Does that make sense?

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Re: A540 (or R260) 4MB card

Post by cmorley » Wed May 06, 2020 6:00 pm

IIRC the address lines to the MEMC are used to configure the MEMC registers. So I don't think you can swap any of the A<x> and expect it to work.

There is a MEMC data sheet floating around on the internet. I have a PDF I can send if you don't have it already/can't find it. The old ARM databook has MEMC info in too IIRC.

With DRAM you can swap the Ra<x> and the data bits as long as you keep they bytes together with the correct CAS, as you say.

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Re: A540 (or R260) 4MB card

Post by IanS » Wed May 06, 2020 6:05 pm

cmorley wrote:
Wed May 06, 2020 6:00 pm
IIRC the address lines to the MEMC are used to configure the MEMC registers. So I don't think you can swap any of the A<x> and expect it to work.

There is a MEMC data sheet floating around on the internet. I have a PDF I can send if you don't have it already/can't find it. The old ARM databook has MEMC info in too IIRC.

With DRAM you can swap the Ra<x> and the data bits as long as you keep they bytes together with the correct CAS, as you say.
I have a MEMC data sheet pdf (still managed to get the power pins wrong).

I think you have confirmed all my questions. Thanks.

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Re: A540 (or R260) 4MB card

Post by IanS » Sat May 23, 2020 2:14 pm

Version 2.
IMG_20200523_134902.jpg
IMG_20200523_134957.jpg
Needed a bit of rework on a couple of joints, But I'm fairly happy for my first attempt with solder paste, stencil and hot-air.
Now need to see if it was just beginners luck.

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Re: A540 (or R260) 4MB card

Post by steve3000 » Sat May 23, 2020 2:56 pm

=D> that looks really good! All working OK?

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Re: A540 (or R260) 4MB card

Post by IanS » Sat May 23, 2020 3:03 pm

steve3000 wrote:
Sat May 23, 2020 2:56 pm
=D> that looks really good! All working OK?
Passed all my usual tests and the test which showed the issue with the A3000 upgrades.
When I get another made, I'll be looking for a volunteer to test it. I only have one A540, so it would be nice to see if it works in other machines.
Need to salvage some more ram chips from SIMMs first.

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Re: A540 (or R260) 4MB card

Post by steve3000 » Sat May 23, 2020 3:08 pm

IanS wrote:
Sat May 23, 2020 3:03 pm
steve3000 wrote:
Sat May 23, 2020 2:56 pm
=D> that looks really good! All working OK?
When I get another made, I'll be looking for a volunteer to test it. I only have one A540, so it would be nice to see if it works in other machines.
I'd be more than happy to offer my A540's final 4mb slot for testing :)

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Re: A540 (or R260) 4MB card

Post by RobC » Sat May 23, 2020 3:56 pm

Happy to test too if you want a bigger sample of machines.

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Re: A540 (or R260) 4MB card

Post by AndyMc1280 » Sat May 23, 2020 4:53 pm

IanS wrote:
Sat May 23, 2020 3:03 pm
Passed all my usual tests and the test which showed the issue with the A3000 upgrades.
When I get another made, I'll be looking for a volunteer to test it. I only have one A540, so it would be nice to see if it works in other machines.
Need to salvage some more ram chips from SIMMs first.
I have a 16MB R260 and FPU with a mixture of cards. Would also be happy to help test :D

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Re: A540 (or R260) 4MB card

Post by IanS » Sun May 24, 2020 11:48 am

I had a relatively productive evening (even had a power cut mid-way through)
IMG_20200524_112703.jpg
No rework required on the extra two.
IMG_20200524_112753-001.jpg
IMG_20200524_112753-001.jpg (16.84 KiB) Viewed 590 times

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Re: A540 (or R260) 4MB card

Post by AndyMc1280 » Sun May 24, 2020 6:25 pm

very nice :shock: :)

Stable ? My 16MB isn't.....

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Re: A540 (or R260) 4MB card

Post by IanS » Sun May 24, 2020 6:58 pm

AndyMc1280 wrote:
Sun May 24, 2020 6:25 pm
Stable ? My 16MB isn't.....
I'm open to suggestions for things to try. I don't have anything very sophisticated.
Fill memory with pseudo random data, check it reads back correctly. It will sit and run this for hours, lmiting factor, wanting to do something else.
Fill memory with random data (random seed value) data, save it to disk, repeat n times, read files back, check data is correct. n is configurable. Repeat whole test until I get bored watching it.
I should probably make a version that works on bytes rather than words and one that uses load/store multiple registers, to test sequential access (does that make sense?).

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Re: A540 (or R260) 4MB card

Post by IanS » Wed May 27, 2020 3:07 pm

steve3000 wrote:
Sat May 23, 2020 3:08 pm
IanS wrote:
Sat May 23, 2020 3:03 pm
steve3000 wrote:
Sat May 23, 2020 2:56 pm
=D> that looks really good! All working OK?
When I get another made, I'll be looking for a volunteer to test it. I only have one A540, so it would be nice to see if it works in other machines.
I'd be more than happy to offer my A540's final 4mb slot for testing :)
I've sent a board to Steve for testing, and I have some more MEMC chips on the way to populate the other boards.

Watch this space.

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Re: A540 (or R260) 4MB card

Post by cmorley » Wed May 27, 2020 3:42 pm

=D>

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Re: A540 (or R260) 4MB card

Post by steve3000 » Thu May 28, 2020 3:26 pm

IanS wrote:
Wed May 27, 2020 3:07 pm
I've sent a board to Steve for testing, and I have some more MEMC chips on the way to populate the other boards.

Watch this space.
IMG_0814.jpg
Received and fitted this afternoon :)

Computer didn't start up on first attempt after fitting, but I put that down to it being very fussy whenever I move anything in/around the floppy drive, due to (I think) the power cable for the floppy starting to fail and that intermittent connection confusing the HD disc interface podule...

Anyhow, after wiggling the floppy power connector, everything booted correctly and 16Mb available on the desktop. More testing will commence later today.

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Re: A540 (or R260) 4MB card

Post by IanS » Mon Jun 01, 2020 11:06 pm

IanS wrote:
Sat May 02, 2020 3:16 pm
There definately was a tech note from Acorn about timing parameters with multiple MEMCs. Steve Picton remembers seeing it, but can't find a copy. The MEMC chips in my Simtec cards have a hand written value (like "18.0") on them, which I always assumed was the result of testing.
Does any have a copy of the Acorn engineering note about MEMC timing? I'd really like to understand what the "18.0" is about.

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Re: A540 (or R260) 4MB card

Post by steve3000 » Tue Jun 02, 2020 8:21 am

IanS wrote:
Mon Jun 01, 2020 11:06 pm
Does any have a copy of the Acorn engineering note about MEMC timing? I'd really like to understand what the "18.0" is about.
I've not seen the engineering note, but on checking my 8mb A5000, I found the MEMCs on its Simtec 4-8mb card both have "18.4" written on them.
DSC_4920.JPG
Simtec MEMC card with "18.4" on each MEMC
The "monster A3000" build also has a Simtec 4-8mb A5000 upgrade fitted, but the MEMCs on that don't have anything written on them (possibly removed by previous owner restoring/cleaning?).

Checking my A540's two Acorn 4mb cards, both have nothing hand-written or stamped on them - but the MEMC on the A540 PCB does:
DSC_2352.JPG
A540 PCB MEMC stamped with "2201,393"

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Re: A540 (or R260) 4MB card

Post by IanS » Wed Jun 03, 2020 4:44 pm

IanS wrote:
Mon Jun 01, 2020 11:06 pm
IanS wrote:
Sat May 02, 2020 3:16 pm
There definately was a tech note from Acorn about timing parameters with multiple MEMCs. Steve Picton remembers seeing it, but can't find a copy. The MEMC chips in my Simtec cards have a hand written value (like "18.0") on them, which I always assumed was the result of testing.
Does any have a copy of the Acorn engineering note about MEMC timing? I'd really like to understand what the "18.0" is about.
Or anyone with a simtec A540 4MB card, can they have a look and report back the hand-written value from the MEMC chip.

Thanks.

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Re: A540 (or R260) 4MB card

Post by steve3000 » Thu Jun 04, 2020 12:04 am

Attached is my memory test code, which might be useful for testing these :)

For details, see the ReadMe file in the Zip.
MemTest.zip
MemTest v0.02
(4.96 KiB) Downloaded 3 times

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Re: A540 (or R260) 4MB card

Post by IanS » Thu Jun 04, 2020 12:17 am

steve3000 wrote:
Thu Jun 04, 2020 12:04 am
Attached is my memory test code, which might be useful for testing these :)

For details, see the ReadMe file in the Zip.

MemTest.zip
Thanks, I'll give it a go.
Are the patterns all random, or are test patterns (walking ones, all 1's, all 0's, one byte &ff etc.) incuded? Any Byte access, word access, sequential access (STM, LDM)?

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Re: A540 (or R260) 4MB card

Post by steve3000 » Thu Jun 04, 2020 8:06 am

RAM is tested in blocks of 128kb, by filling 128kb with a 32bit pattern using STM, then testing by loading with LDM and comparing. Currently four patterns are used, in the following sequence:

1) 010101010101010101010101
2) 000000000000000000000000
3) 111111111111111111111111
4) 101010101010101010101010

It’s quite easy to add different patterns and switch to STR/LDR or STRB/LDRB, as all the relevant code is already present, just need to call. Let me know how your test goes and I can add the bye/word tests later today.

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Re: A540 (or R260) 4MB card

Post by BeebMaster » Thu Jun 04, 2020 2:16 pm

IanS wrote:
Mon Jun 01, 2020 11:06 pm
IanS wrote:
Sat May 02, 2020 3:16 pm
There definately was a tech note from Acorn about timing parameters with multiple MEMCs. Steve Picton remembers seeing it, but can't find a copy. The MEMC chips in my Simtec cards have a hand written value (like "18.0") on them, which I always assumed was the result of testing.
Does any have a copy of the Acorn engineering note about MEMC timing? I'd really like to understand what the "18.0" is about.
This FCO appears to acknowledge the issue but doesn't go into any specifics:

http://4corn.co.uk/archive//acornftp/fco/fco2031.txt
Image

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Re: A540 (or R260) 4MB card

Post by IanS » Thu Jun 04, 2020 8:54 pm

BeebMaster wrote:
Thu Jun 04, 2020 2:16 pm
This FCO appears to acknowledge the issue but doesn't go into any specifics:

http://4corn.co.uk/archive//acornftp/fco/fco2031.txt
Inyteresting find, thanks.

My PAL/GAL is an -01, does anyone have a -02. I'm guessing they are both protected, so not easy to see what changed.

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