Open source A3020 RAM

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cmorley
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Open source A3020 RAM

Post by cmorley » Tue Sep 03, 2019 6:23 pm

Schematic & gerbers here
Fitting


I've drawn and ordered some PCBs for new A3020 RAM. Zarchos is funding the prototypes & once tested I will release all the design files & Gerbers.

I might make some up for forum members too if there is any interest.

I am using a sister chip to the one I used on the A3000 RAM I did with a small adapter board to the pin headers. Hopefully I got the dimensions right - if not I will have to redo the board.
Photo0791.jpg
Testing.. I don't have an A3020. IanS came up with a good test method of copying large (>90MB) files from the supervisor which uses all the RAM when thesting the A3000 RAM. Any volunteers? It can be scripted with an OBEY file but needs to run for hours :S

Chris
Last edited by cmorley on Sat Feb 29, 2020 5:39 pm, edited 2 times in total.

steve3000
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Re: Open source A3020 RAM

Post by steve3000 » Tue Sep 03, 2019 7:07 pm

As for the A5000, I'd be happy to volunteer...great excuse to find my A3020 in the loft!

I also have the Acorn RAM test ROMs, which offer a fairly rigorous cyclic RAM test...

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IanS
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Re: Open source A3020 RAM

Post by IanS » Tue Sep 03, 2019 7:12 pm

steve3000 wrote:
Tue Sep 03, 2019 7:07 pm
I also have the Acorn RAM test ROMs, which offer a fairly rigorous cyclic RAM test...
They never found an issue with the A3000 RAM, which showed up errors via large file copying. The file copying was the first thing I could think of to check the RAM, I'd hope there are better options. Anyone fancy porting MEMTEST86?
Last edited by IanS on Tue Sep 03, 2019 8:41 pm, edited 1 time in total.

steve3000
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Re: Open source A3020 RAM

Post by steve3000 » Tue Sep 03, 2019 7:20 pm

IanS wrote:
Tue Sep 03, 2019 7:12 pm
steve3000 wrote:
Tue Sep 03, 2019 7:07 pm
I also have the Acorn RAM test ROMs, which offer a fairly rigorous cyclic RAM test...
They never found an issue with the A3000 RAM, which showed up errors via large file copying. The file copying was the first think I could think of to check the RAM, I'd hope there are better options. Anyone fancy porting MEMTEST86?
That's interesting about the ROMs... thinking about it, they're also 32pin 8-bit ROMs so would need some work to get into the A3020... so file copying sounds best.

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IanS
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Re: Open source A3020 RAM

Post by IanS » Tue Sep 03, 2019 7:26 pm

steve3000 wrote:
Tue Sep 03, 2019 7:20 pm
That's interesting about the ROMs... thinking about it, they're also 32pin 8-bit ROMs so would need some work to get into the A3020... so file copying sounds best.
Mine were only 28-pin - viewtopic.php?f=16&t=12252&p=156202#p155802
Do you have a different version?

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Re: Open source A3020 RAM

Post by cmorley » Tue Sep 03, 2019 7:47 pm

File copying was necessary to get the failure because of the extra noise on the A3000 ground.

Without the IDE activity the poor signal ground on the A3000 MEMC caused all low signals to be raised on falling edges of MEMC output pins... with the IDE going this tipped it over the TTL threshold causing the DRAM to detect a RAS edge. I never did investigate if it was the A3000 PCB layout or insufficient ground pins on the MEMC - would have been easy enough to solder to the MEMC GND pin and scope that but I ran out of enthusiasm!

I am also pretty sure it was only memory reads too - so the machine ran and never crashed but we got bit errors in the file copy. I can't quite remember.

So... IDE activity is a good memory test.

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Re: Open source A3020 RAM

Post by cmorley » Fri Sep 06, 2019 8:25 am

Two boards complete. The hole is to allow access to LK32 on the motherboard. Hopefully the dimensions are correct.
Photo0793.jpg

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trixster
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Re: Open source A3020 RAM

Post by trixster » Thu Sep 12, 2019 8:25 am

Looks great! Is this using faster ram to allow for an A3020 overclock?

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Re: Open source A3020 RAM

Post by cmorley » Thu Sep 12, 2019 9:00 am

Potentially... if it works in the system. :?

The timings for key parameters are faster at typically 60% of the 80ns Toshiba TC514800. So as long as the RAM is compatible then there should be decent headroom for overclocking...

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Re: Open source A3020 RAM

Post by cmorley » Tue Sep 17, 2019 6:46 pm

Steve has done a bunch of testing and it doesn't work in an A4000 reliably. I imagine it is exactly the same problem as the A3000 but I was hoping the ARM250 SoC would have had better signal integrity :(

So buffer version ready to test at ABUG. If it works I will redo the PCBs and work out how to fit 11 buffers on the tiny boards :S
Photo0800.jpg
I adapted one of the A5000 boards which has space for all the buffers. Hopefully good enough for a proof of concept.

Buffers will take some of the overclock performance away but perhaps not too terrible because the RAS and A0-9 have good setup time margin IIRC and I don't buffer CAS... time and testing will tell.

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Re: Open source A3020 RAM

Post by steve3000 » Tue Sep 17, 2019 8:46 pm

Wow, I love that spider RAM... Now that's what proper upgrades look like =D>

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Re: Open source A3020 RAM

Post by cmorley » Sat Sep 21, 2019 6:55 pm

spider RAM doesn't work :( I think the long wires are just too poor for crosstalk/signal integrity. I will do a new PCB with the buffers on board.

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Re: Open source A3020 RAM

Post by cmorley » Mon Sep 23, 2019 4:33 pm

New PCB design with buffers on. I'll double check it tomorrow and then place an order.
Top:
A3020ramtop.png
Bottom:
A3020rambottom.png

steve3000
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Re: Open source A3020 RAM

Post by steve3000 » Mon Sep 23, 2019 6:42 pm

Looks great, is that the same size footprint?

cmorley
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Re: Open source A3020 RAM

Post by cmorley » Mon Sep 23, 2019 6:48 pm

steve3000 wrote:
Mon Sep 23, 2019 6:42 pm
Looks great, is that the same size footprint?
Yes. It all looked very tight at the weekend in XLT's A4000 so I tried hard to keep the PCB outline the same. The "Acorn A3020 RAM" text on the top was a casualty though...

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Re: Open source A3020 RAM

Post by steve3000 » Mon Sep 23, 2019 6:52 pm

cmorley wrote:
Mon Sep 23, 2019 6:48 pm
steve3000 wrote:
Mon Sep 23, 2019 6:42 pm
Looks great, is that the same size footprint?
Yes. It all looked very tight at the weekend in XLT's A4000 so I tried hard to keep the PCB outline the same. The "Acorn A3020 RAM" text on the top was a casualty though...
Ah ok. Might want to say "A4000/A3020" RAM?

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Re: Open source A3020 RAM

Post by Kazzie » Mon Sep 23, 2019 9:22 pm

steve3000 wrote:
Mon Sep 23, 2019 6:52 pm
cmorley wrote:
Mon Sep 23, 2019 6:48 pm
steve3000 wrote:
Mon Sep 23, 2019 6:42 pm
Looks great, is that the same size footprint?
Yes. It all looked very tight at the weekend in XLT's A4000 so I tried hard to keep the PCB outline the same. The "Acorn A3020 RAM" text on the top was a casualty though...
Ah ok. Might want to say "A4000/A3020" RAM?
But that'll take up even more space! :)
BBC Model B 32K issue 7, Sidewise ROM board with 16K RAM
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Re: Open source A3020 RAM

Post by steve3000 » Mon Sep 23, 2019 11:15 pm

#-o

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vanpeebles
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Re: Open source A3020 RAM

Post by vanpeebles » Tue Sep 24, 2019 8:32 am

Are we any closer to a turbo ram style upgrade? :) I would love one for my old A3010 [-o<

cmorley
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Re: Open source A3020 RAM

Post by cmorley » Sat Oct 19, 2019 2:29 pm

Fresh from soldering (I didn't even clean the flux off) A3020 RAM with buffers under test in an A4000.

Booted and detected 4096KB. Now running IanS's large file copy test test.
Photo0825.jpg

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IanS
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Re: Open source A3020 RAM

Post by IanS » Sat Oct 19, 2019 3:35 pm

cmorley wrote:
Sat Oct 19, 2019 2:29 pm
Fresh from soldering (I didn't even clean the flux off) A3020 RAM with buffers under test in an A4000.

Booted and detected 4096KB. Now running IanS's large file copy test test.
And... what is the result?

Looks good, those buffers look closely packed together.

Fingers crossed here.

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Re: Open source A3020 RAM

Post by cmorley » Sat Oct 19, 2019 3:50 pm

IanS wrote:
Sat Oct 19, 2019 3:35 pm
And... what is the result?
Only 4 rounds completed so far Ian. We managed quite a few at Cambridge in this machine with the no buffer board so I'm not chicken counting just yet!

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Re: Open source A3020 RAM

Post by cmorley » Sat Oct 19, 2019 6:17 pm

10+ cycles of the test now and zero errors so that is good.

I will clean these boards and send them to Steve3000 next week to confirm they work in his machine. I am confident they will.

This testing has been done on an A4000 so it would be good to get some testing on an A3020 & confirm that they (a) work (b) fit. I think we need a volunteer for that... (IIRC steve3000 was using an A4000 too).

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Re: Open source A3020 RAM

Post by IanS » Sat Oct 19, 2019 8:24 pm

cmorley wrote:
Sat Oct 19, 2019 6:17 pm
10+ cycles of the test now and zero errors so that is good.
Excellent news. Lets hope it's the same on an A3020 (which I don't own, or I'd volunteer to help)

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Re: Open source A3020 RAM

Post by cmorley » Fri Oct 25, 2019 9:56 am

Here is a photo of the tested working version. This should work in steve3000's machines now & I will post it to him soon so he can have a try. It still hasn't been tested in an A3020...
Photo0826.jpg
Once the testing is complete I'll release the Gerbers. I will also make a small batch to order as a one off thing.

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Re: Open source A3020 RAM

Post by cmorley » Sun Jan 05, 2020 12:51 pm

OK testing has gone well & they seem fine. Only question left is how well the overclock. I will try to answer this on an A4000 before the January ABUG.

I will make one batch of these by order for stardotters. They won't be an ongoing product from me. Please don't respond to this thread I will post a sales thread soon after the overclock test results.

Schematic:
A3020_2.pdf
(89.45 KiB) Downloaded 40 times
Gerbers:
A3020_2.zip
(200.03 KiB) Downloaded 25 times
There are so few parts I didn't put a BOM together per se. All the part numbers are on the schematic. Contact me if you need more details. The source is open and I can send the original diptrace files (or export to another CAD system) on request. Thanks to Xavier Tardy for commissioning this project on behalf of the 32-bit Acorn community.

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Re: Open source A3020 RAM

Post by SimonSideburns » Sun Jan 05, 2020 7:10 pm

Would you like me to ferret around in the attic and try to find one of my A3020s to bring along to ABUG this month?

I might bring both (if I can find them) as they both might have original batteries inside which I really ought to have removed years ago.
Just remember kids, Beeb spelled backwards is Beeb!

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Re: Open source A3020 RAM

Post by alexgibson » Tue Jan 07, 2020 12:21 am

That is a very neat and tidy looking board, I like the cut-out for easy prising!

Very nice job :)

cmorley
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Re: Open source A3020 RAM

Post by cmorley » Tue Jan 07, 2020 7:01 am

SimonSideburns wrote:
Sun Jan 05, 2020 7:10 pm
Would you like me to ferret around in the attic and try to find one of my A3020s to bring along to ABUG this month?

I might bring both (if I can find them) as they both might have original batteries inside which I really ought to have removed years ago.
Well if you can that might be handy. The boards have only been tested in an A4000. Electrically A3020 and A4000 are very similar so I am confident they will function. What has not been tried is they physical fit in an A3020 :|
alexgibson wrote:
Tue Jan 07, 2020 12:21 am
I like the cut-out for easy prising!
:shock:

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SimonSideburns
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Re: Open source A3020 RAM

Post by SimonSideburns » Tue Jan 07, 2020 2:13 pm

I'll get up in the loft and do some rummaging on the next rainy day we have. Yay, that's today.

If you don't hear from me later this evening please send rescuers.
Just remember kids, Beeb spelled backwards is Beeb!

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