SD Interface for Plus 1

[Ramtop]

Hi All,

The question that most comes up when people ask me about the ElkSD64 is "does it work with a plus 1?". To which the answer is, of course, no. But it got me thinking about doing something that would fit a Plus 1, especially when I obtained one thanks to the excellent Mr Dave Hitchins, of this parish.

After some false starts and much head scratching over Acorn's often less than precise documentation, I've now got something that works. It's basically a cut-down ElkSD64, with only 16K of flash and SW RAM as opposed to 32K of each on the ElkSD64. Just enough to run the sideways version of MMFS.

Pictures are of the prototype, which is fully functional. Final boards will have gold plated contacts, the prototype is just HASL as I'm cheap and didn't want to spend any more than necessary on PCBs that may not have worked at all.

The hardware is mostly now fixed except for minor tweaks but there's still some room to add to the CPLD programming. I'm thinking of a register to switch out the default SW MMFS and boot with the standard version, which would free up the 16K of SW RAM for other use while retaining SD capability. I'm hoping to have a very limited number of finished boards available by the end of the month or early next month.

[daveejhitchins]

Great work, Gary . . .

Noticed you’ve placed the components on the side facing the keyboard (not that it, probably, matters with surface mount components?). This will give you the minimum space in the cartridge slot - especially with a case around it!

If it would help(?) I can send you templates for two sizes of PCB, the ‘standard’ Acorn Cartridge case and the 3D cartridge case design that I use. Let me know . . .

Dave H

[CMcDougall]

[Ramtop]

Noticed you’ve placed the components on the side facing the keyboard (not that it, probably, matters with surface mount components?). This will give you the minimum space in the cartridge slot - especially with a case around it!

For once I actually planned ahead here and measured to make sure it'll fit!

The final board won't have the pin headers, so the tallest component is the SRAM at 2mm tall. Combined with the case wall I only need 4.5mm clearance from the PCB, which the cartridge slot accommodates easily.

[0xC0DE]

[Elk2019]

I am already the proud owner of your superb Electron MicroSD Interface Mk2.
Having recently acquired a Plus-1 expansion unit, I was delighted to learn that you have created an SD Interface for the Plus 1. I will definitely be getting one. Then I will finally be able to play some games using a joystick! What will base PAGE memory be set at and will the finished product have a case?

[Ramtop]

For the Plus 1 board PAGE will be at &E00. The cartridge has 16K of sideways RAM on it so none of the Electron's memory is used up.

Current plan is there will be a case (same colour and general look as the ElkSD64) but I'm not sure if the first batch will have cases by default, it may be an optional extra. Making cases for the ElkSD64 is presently keeping my 3D printer very busy indeed, not sure how many Plus 1 cases I can squeeze in. If interest in the first batch is strong enough to justify it I may grit my teeth and invest in a second printer.

PCBs for the initial batch have been ordered. I'll post when I have something more to show

[mr-macrisc]

You can pop me down for one.

Is this a cartridge that will work in master and elk?

Regardless if it’s master/elk or elk only my name is a defo on list please

John

Ps wee though if it’s elk only why not a wee switch and couple extra tracks to make it work in both?

[Ramtop]

It only works in the Elk, I'm afraid. Hardware wise, you're right, it's not a big deal to make the board Master compatible. But actually getting it to work would require more complexity in the CPLD programming and a master version of MMFS stored in the flash chip.

Now, this isn't insurmountable. I over-specced the CPLD (it has twice the logic of the one used in the ElkSD64 and more IOs) so I can add new stuff, and there are holes for a jumper on the PCB that could be used to switch the flash between Elk and Master versions of MMFS; the Master MMFS would need to be a Frankenstein hybrid of the normal Master MMFS and the Electron EPP hardware driver (as that's the interface the card implements for driving the SD card), no idea if that will work on not.

But none of that is a priority because...tada...there's probably going to be a specific Master SD cartridge. Because the Master has plenty of RAM on board a Master-only cartridge can do away with the SRAM chip and use a small CPLD with less IOs, so it will be cheaper to build. I've designed and ordered the PCBs for this, it's really a question of whether I can cobble together a build of MMFS that will work with it. My 6502 coding skills are not the best and I'm reluctant to do more than minimal modifications to the code.

PCBs for both the ElkSD-Plus1 and the Master board are in production and I hope to have them late next week. I've also printed the first case, it's ugly but it works and unlike the ElkSD64 it uses screws rather than glue. Also managed to get paging working on the prototype ElkSD-Plus1 board, so 64K of flash and 32K of RAM can be accessed by writing to a register; I'm thinking of putting multiple versions of MMFS in flash. I'd really like to have both standard MMFS and MMFS2 on board, selectable either by jumper or by a register write.

[marcusjambler]

Please put me down for one built board

[Elminster]

But none of that is a priority because...tada...there's probably going to be a specific Master SD cartridge.

Darn now I will have to update the hardware list again for Master version

[Steve1234]

Put me down for 1 please

[0xC0DE]

I think it was pretty clear I'm interested in buying one, right?

By the way, I'm also interested in the Master version. Is it at all possible to create one that keeps PAGE at &E00 and does not use any kind of RAM of the Master itself, i.e. to have SWRAM on the Master version as well? Some games and most notably demos need all the RAM they can get their hands on (looking at you Bitshifters)

[Ramtop]

Thanks for all the expressions of interest! They've given me enough confidence to up the first batch size; I was only going to do half a dozen Plus 1 boards, but that clearly isn't going to be enough.

The Master version is still very much up in the air right now. The simple no-RAM Master specific board ("MasterSD" as I'm imaginatively calling it) is really intended as something that can be sold cheaply on Ebay for people who've bought a Master and just want a memory card interface that doesn't require opening the computer up to fit a ROM and fiddling about underneath with cables. Barring a technical issue this one will almost certainly go ahead; the design has 100% component commonality with the ElkSD64, so I won't get stuck with a pile of useless components if it doesn't sell. The only risk is the PCBs, which are relatively cheap.

I may -- thinking out loud, here -- also do something for the Master with some RAM on it. Possibly a tweak of the ElkSD-Plus1 PCB (which isn't Master compatible in its current form). But that is still some way off, finishing the ElkSD-Plus1 has priority at the moment.

[0xC0DE]

No problem. We can wait an extra week

[mr-macrisc]

Brilliant, will likely be having one of each then

[Ramtop]

Small update. I've been miserably, wretchedly sick for much of the past week so not much progress to report. However, the batch of PCBs I ordered have arrived. The ElkSD-Plus1 boards look very natty with their gold plating and I'll be building some for testing at the weekend.

I also ordered a few test boards to see if the whole cheap no-RAM Master SD cartridge idea would fly. I quickly soldered one up tonight and it seems to work

I'm loading and saving on the Master with the test board in a cartridge slot, driven by MMFS using the simple Electron EPP hardware driver. Caveat; I've done no real testing, the board has been alive for all of half an hour at this point, and I'm out of suitable SMD flash chips so MMFS is on an EPROM in the Master rather than loading from the cartridge. I don't expect that to be an issue, though. Still not sure if this board will ever become an actual thing people can buy, but confirmation that the idea is sound makes a Master version of the ElkSD-Plus1 very likely.

[rharper]

I look forward to having one of each.
Ray

[rodonn]

Will this be on e-bay?

[Ramtop]

Yes, it will. Probably in around a week or so.

Anyway, news: the ElkSD-Plus1 is finished, yay!

I've built the first board on the production PCB design and the CPLD programming is done, so that's pretty much it bar writing the documentation. There's good news and bad, however.

Taking advantage of the oversize CPLD I've altered how MMFS is stored; on the prototype card I used the bootstrap version of MMFS, which lives in a ROM bank and copies itself into a RAM bank at boot. That worked fine, but cartridges are limited to two sideways banks and so both were consumed by MMFS. The final card does away with this in favour of a single split ROM/RAM bank - the lower section of the bank is ROM containing the sideways version of MMFS, but the upper area is mapped to RAM and is used by MMFS as workspace. Using this approach means MMFS needs only a single bank, leaving the second one free. It's configured as RAM, so the ESD-Plus1 now also acts as a 16K SWRAM expansion.

I've found a use for the jumper pins on the board, too. The ESD-Plus1's flash ROM will ship with three separate versions of MMFS, the presence of a jumper on pins 1 and 2 selects between to first two - my intention is for these to be MMFS 1.4x (as the default) and MMFS 2. People just wanting to play games can stick with 1.4x while MMFS 2 is available for anyone who hates dealing with the beeb.mmb file and doesn't mind the game menu compatibility hit that MMFS 2 entails.

A jumper on pins 2-3 puts the cartridge into recovery mode, which will boot the third copy of MMFS even if the first two have been trashed by a bad flash update. For convenience the jumpers can be temporarily overridden by setting bits in a configuration register.

The bad news is there's going to be a big old ugly patch resistor soldered to the back of the PCB, because I goofed. I designed the jumpers as pull-ups, when they needed to be pull-downs. This is fixed by bodging on the resistor. Also, it's very likely I can't build enough cases so ESD-Plus1s sold via to for sale forum will initially just be naked PCBs without cases. I'll put up the STL file for the case on my website for anyone with a 3D printer.

I'm hoping to have boards available by next weekend, but I'm presently lacking CPLDs because Farnell managed to mess up the order I placed last week and my chips are stuck in some kind of limbo.

[0xC0DE]

Great news!!
I like the extra SWRAM available now.
I'm hoping to buy one from you with a case.
Sending you a DM now.

[Ramtop]

Finally the first batch of ElkSD-Plus 1s are finished, I should have a thread up in the For Sale forum later today or tomorrow for anyone interested in ordering one.

The card obviously has an SD interface, plus 16K of sideways RAM available for user use, and no less than three copies of MMFS in flash. MMFS 1.43 is the default, MMFS 2 (no beeb.mmb file needed) can be accessed by removing a jumper. The third copy of MMFS is a for recovery if the first two are corrupted by a bad flash update, it is also accessed by a jumper. MMFS uses a split ROM/RAM bank to conserve resources.

Both cased and uncased versions will be available, the cases are built on demand so may delay dispatch by a day or two. There are two colours, the 'pale ivory' that anyone with an ElkSD64 will be familiar with, and 'acorn green', which is the closest I could get to the colour of the Acorn logo on the Elk. Ivory hides the imperfections of 3D printing better, but I personally prefer the green.

The hardware works fine, however there is basically no documentation beyond basic installation instructions at this point. Still working on that.

[Elk2019]

What can I say? Amazing. Fantastic. Superb. Mega....when/where can I get one from?

[Steve1234]

Put me down for one please.

There's no reason why it wouldn't work with a Plus 3 fitted is there?

[Ramtop]

What can I say? Amazing. Fantastic. Superb. Mega....when/where can I get one from?

viewtopic.php?f=8&t=18189

There's no reason why it wouldn't work with a Plus 3 fitted is there?

I can't see any reason why not. It's not doing anything unusual.

[Elk2019]

Thank you Ramtop Finally got round to testing the Elk SD Plus1 interface. It works brilliantly and I can now use a joystick! (on certain games).

Also bought the excellent ElkSD64 interface, which expands the humble Elk to 64kb !

These products enable users to relive those classic games without the pain of lengthy tape loading times. If you consider yourself a serious retro Electron gamer, then get one of these cool devices.

A big thank you to Ramtop for continuing to support retro hardware and I really appreciate all the time and effort he is invested in producing these NEW products for the Elk.

[0xC0DE]

Well said. Couldn't agree more. I got all 3 most recent versions of the ElkSD from ramtop and they are excellent products!

[Ramtop]

Thank you very much for the kind words!

Pretty much every major retro machine has reasonably priced SD interfaces now and I don't see why the Elk should be left out. And thanks to the assistance I've received from people here on stardot I'm happy to be able to help with that a bit.

[*TAPE]

Can I still get one of these from you, Ramptop?
....if so, how can I get one?


Apologies for resurrecting an old post.... My PMs are not enabled yet.

[gavinlew]

Should be able to buy them on eBay, bought mine there this month