Should I make a batch for anyone who wants one? You would need to buy a Teensy 4.1 and load the Arduinio/Teensyduino tools on your PC.

I'd be interested. I've adapted an RTOS to run on the T4.1 and have my own USB host library, so I'd be curious to see what else could be done with it - thinking specifically about adlib, MPU-401 and joystick support. I've also got a couple of custom Teensys with 32MBs of onboard SDRAM.

PM sent to @jmarsh

Quick update: The XTMax driver was updated to support 16 MB of Expanded RAM when two PSRAM chips are installed on the Teensy 4.1 board.

I am also very interested. Does it support UMB?

wondow wrote on 2025-02-05, 00:11:

I am also very interested. Does it support UMB?

I'm wondering the same thing. I don't see any reference to UMB support on GitHub, but it shouldn't be too difficult to add, right?

I've been looking for upgrades for a Tandy 1000 EX with 256MB on-board RAM. I already ordered an ISA riser card for it on Tindie. I was thinking about upgrading it with a PicoMEM, but that card can only add 128KB with 0 waitstates, adding at least 4 wait states to any additional RAM on top of that. That doesn't seem very appealing, since the whole point of the upgrade is to be able to run later and more demanding games on it.

But on the other hand, the PicoMEM also supports UMB, and can also emulate a mouse, as well as some sound devices and a network card.

Perhaps I should combine an XTMax with a PicoMEM (taking up both ISA slots on the riser card), to get the best of both worlds, even if these two boards have some overlapping features? After all, I also need to add mouse support to the machine, and it doesn't have an on-board serial port.

I've also considered a Lo-tech 1MB RAM Board for maxing out conventional and upper memory, but only TexElec sells those, and I prefer not to order things from so far away, with high shipping costs and import taxes.

Where can I order an XTMax, by the way? Are you taking orders right now?

Thanks for making and sharing this, by the way!

Correct, the XTMax can increase conventional RAM up to 640 KB with zero wait state. It is auto-sensing so no jumpers or BIOS settings are needed.

XTMax is much easier to use than the alternatives. You just plug it in and you get full zero wait-state 640 KB, 16 MB of expanded RAM, and bootable MicroSD which doest rely on disk images so you can just copy files directly over from your PC/Mac/Linux/Chromebok. It provides the max functionality of three ISA cards in one.

Maybe someday I can add mouse, USB, sound, or networking to the XTMax, however I dont think they are particularly interesting. I never needed any of these features when using my IBM XT years ago. What I did use was increased memory and a hard disk, all of which XTMax supports very well. XTMax also does not interfere with existing floppy and hard disks like other solutions do.

I wouldn't spend money on the single-function Lo-tech boards at this point when you can get more functionality from a board like XTMax.

I reached out to TexElec a few times to distribute the XTMax but they did not extend the courtesy of a response so the best (and least expensive) way to get an XTMax is to build the PCB from JLCPCB with my files on GitHub. I paid $30 USD for them to build the PCB, solder on the chips, and ship five boards, so I think this is the least expensive way to get one. DM me if you need some help.

MicroCoreLabs wrote on 2025-02-22, 20:11:

Correct, the XTMax can increase conventional RAM up to 640 KB with zero wait state. It is auto-sensing so no jumpers or BIOS settings are needed.

When there is no VGA card, an extra 64k could be used.
Dependent on the amount of bios roms, Upper memory blocks could also be made available.

Could the XTMax allow for this larger memory expansion or are its memory resources already maxed out ?

I have been reluctant to use the XTMax, simply because it wasn't clear if RTC is supported. I've been reading a bit, I see it does, and it looks like it's not hard to support it. Could we add the code for it, and people can decide to use the Teensy's RTC or not when they program it? As a replacement for the SixPackPlus or Quadboard, you'll loose your RTC support, and those few ISA cards that only have RTC kind of defeats bothering. The only other alternative would be to piggyback the BIOS or CPU chip or something, and no one known is making such modules now, right?

>>Could the XTMax allow for this larger memory expansion or are its memory resources already maxed out ?

Yes, very easy to add this. There is plenty of extra RAM to add 64 K more.

the3dfxdude wrote on 2025-02-22, 21:42:

I have been reluctant to use the XTMax, simply because it wasn't clear if RTC is supported. I've been reading a bit, I see it does, and it looks like it's not hard to support it. Could we add the code for it, and people can decide to use the Teensy's RTC or not when they program it? As a replacement for the SixPackPlus or Quadboard, you'll loose your RTC support, and those few ISA cards that only have RTC kind of defeats bothering. The only other alternative would be to piggyback the BIOS or CPU chip or something, and no one known is making such modules now, right?

I can investigate adding this. It is probably as simple as a few lines of code...

Hmm.. just adding a battery to the Teensy will just keep my code running which will burn up the battery very quickly. I think a better solution would be to use an external chip which has a battery to just power itself and not the Teensy.

The battery only keeps the RTC part of the Teensy running, not the entire thing. It's not particularly well-tuned for low current though - batteries last roughly 4 months. So an external RTC will last a lot longer.

Where do you get the teensy boards?
All I can find costs over 50 euros.

This would be interesting project for my euro PC as it only has 512kb memory and only one expansion slot. Currently I've got xtide card installed. (There aren't many games that require 640k and run with nec v20.)
Other project would be picomem but it's not open source 😕.

digger wrote on 2025-02-22, 17:17:

wondow wrote on 2025-02-05, 00:11:

I am also very interested. Does it support UMB?

I'm wondering the same thing. I don't see any reference to UMB support on GitHub, but it shouldn't be too difficult to add, right?

I have been looking at adding UMB support after seeing your message. I did a little bit of prototyping today and I have something that works using USE!UMBS. It needs a little bit of polishing, but overall yes I am confident we can offer UMB with the no-wait-state memory. I am not sure yet on the exact amount we can support. We have about 320KB of available RAM on top of the 640K already emulating conventional memory. That should be more than what we need 😀

Do you have a specific scenario I can test? Right now I have only tested loading a simple TSR in UMB (DOSKEY) and confirmed that it loads high and does relinquish some memory back to DOS programs.

jmarsh wrote on 2025-02-23, 07:51:

The battery only keeps the RTC part of the Teensy running, not the entire thing. It's not particularly well-tuned for low current though - batteries last roughly 4 months. So an external RTC will last a lot longer.

Yes, but the point is the teensy has an RTC itself, and just needs a battery, so might as well use it. I don't need to keep time for 4 months. If I can use the RTC that's already there, I can keep time over a few power cycles, and disconnect the battery if I don't want to drain it. I wouldn't need another RTC for how seldom I might actually want that. Yes, there are still other RTC options, but it was nice when it is already on the same card.

@MicroCoreLabs and @mbucchia are you both working on the XTMax project?

digger wrote on 2025-02-24, 00:01:

@MicroCoreLabs and @mbucchia are you both working on the XTMax project?

XTMax is MicroCoreLabs' design and project.

I have been helping on the drivers side.

MicroCoreLabs wrote on 2025-02-22, 20:11:

I reached out to TexElec a few times to distribute the XTMax but they did not extend the courtesy of a response so the best (and least expensive) way to get an XTMax is to build the PCB from JLCPCB with my files on GitHub. I paid $30 USD for them to build the PCB, solder on the chips, and ship five boards, so I think this is the least expensive way to get one. DM me if you need some help.

It's unfortunate that TexElec didn't even respond. Thanks for sharing everything on GitHub. I take it that the design files contain the BOM in some common industry format, so that I can order a fully preassembled board from most PCB manufacturing services? I prefer to order it from a European one, such as AISLER. (Suggestions and recommendations for other manufacturers are welcome!)

Sorry if I'm asking about obvious things here. I've tried to order open source hardware designs preassembled before, but as awesome that it is that people freely share these designs on GitHub, such designs often lack an automatically parsable BOM, so manual soldering (not to mention having to figure out what parts to order separately) would still be required and I prefer to avoid that, especially when dealing with SMD components.

I'll DM you, as you suggested. Thanks.

By the way, have you considered reaching out to @dreamblaster? Maybe he would be willing to sell your board on Serdashop. He already sells the PicoGUS and PicoMEM cards there. I've bought quite a few items from that site over the years, and I've been quite happy with his service. He's friendly and approachable, both through Vogons and through email.

digger wrote on 2025-02-24, 00:23:

It's unfortunate that TexElec didn't even respond. Thanks for sharing everything on GitHub. I take it that the design files cont […]
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MicroCoreLabs wrote on 2025-02-22, 20:11:

I reached out to TexElec a few times to distribute the XTMax but they did not extend the courtesy of a response so the best (and least expensive) way to get an XTMax is to build the PCB from JLCPCB with my files on GitHub. I paid $30 USD for them to build the PCB, solder on the chips, and ship five boards, so I think this is the least expensive way to get one. DM me if you need some help.

It's unfortunate that TexElec didn't even respond. Thanks for sharing everything on GitHub. I take it that the design files contain the BOM in some common industry format, so that I can order a fully preassembled board from most PCB manufacturing services? I prefer to order it from a European one, such as AISLER. (Suggestions and recommendations for other manufacturers are welcome!)

Sorry if I'm asking about obvious things here. I've tried to order open source hardware designs preassembled before, but as awesome that it is that people freely share these designs on GitHub, such designs often lack an automatically parsable BOM, so manual soldering (not to mention having to figure out what parts to order separately) would still be required and I prefer to avoid that, especially when dealing with SMD components.

I'll DM you, as you suggested. Thanks.

By the way, have you considered reaching out to @dreamblaster? Maybe he would be willing to sell your board on Serdashop. He already sells the PicoGUS and PicoMEM cards there. I've bought quite a few items from that site over the years, and I've been quite happy with his service. He's friendly and approachable, both through Vogons and through email.

I used JLCPCB for this project which was a very smooth process as well as inexpensive. Yes, all of the design files are on my GitHub. You just need to upload the ZIP file that has the Gerber PCB files, and then the two spreadsheets which are the pick and place file as well as the BOM which contains JLCPCB part numbers.

I will also reach out to @dreamblaster as you suggested. Thanks!