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Adapters do exist for using a BlueSCSI with the Portable, on my site. These ones *only* work with BlueSCSI though, and do not present a Molex connector for use with a different drive style.

Yeah, that's the paradox you as the buyer will find yourself in. As a "best practice" I would say you should send the seller a request for lots of pictures. If they are unwilling to open the battery bay, remove any batteries which are present, and take photographs of it from various angles...

1: The Backlit Portable has a similar circuit to the "hybrid", just directly on the motherboard instead of on a dedicated separate PCB. It's very vulnerable to capacitor leakage, as the keyboard/trackball connector next to it has a few capacitors right there. @techknight would know failure...

This is basically what I expected. The RP2040 microcontroller designers made the rather strange design decision to put all IO pins into "pull down" mode at chip startup. This means that the control line (not data) transceivers pull lines low until execution enters our userland code out of the...

That's pretty cool, free CPU accelerator from simply running the expansion RAM faster. Maybe I can stick that into the CPLD somehow, another pin for great acceleration...

In order to assist the BlueSCSI sellers in testing their devices, I created this semi-monstrosity known as either the SCSItron or BlinkyTester or something along those lines. It's the SCSI-est thing I've ever made. It consists of a standard 50 pin SCSI input connector, and presents a bunch of...

The RAM card listing in my shop has been updated with a dropdown. Basic: No switches, always 7 megs of RAM (Except M5126, that one sees 3 without a jumper wire) Switchable: Reworked boards similar to the above picture, until I run out of these and then all in the future will have the switches by...

OK, the mod boards arrived and they look pretty nice. 4 wires to points on the card and it presents the four RAM size modes listed before.

Assuming the issue is caused entirely by the size of the expansion card, yes. It should have the exact same problem. Or in other words, the Portable seems to slow down with expansion RAM cards above a certain size due to what is either a hardware or software bug in the Portable itself.

Mod boards have shipped, once those arrive I'll test the updated firmware some more and update the listing again. I already changed it to point at this thread for clarity on the speed decrease. Likely will have two options after testing, "Plain" and "Switchable". Then going forward, future...

Yeah, no need to rework the whole PCB when there are only a few pins that need tweaking. Future revisions of the RAM card (if they ever sell out) will have the switches by default.

This design is a "modboard", so it would be glued to the main PCB and then it's just four jumper wires. There's no need to order new "full PCBs" since I can just reprogram the CPLD and use a few more of its input pins as configuration.

I have started work on an alternate firmware and switch-mod-PCB for the RAM card. This will allow switching between the following modes: * M5120 "Low RAM" (4MB on expansion card) * M5120 "High RAM" (7MB on expansion card) * M5126 "Low RAM" (3MB on expansion card) * M5126 "High RAM" (7 MB on...

PDS probably doesn't have the perf penalty, because a PDS expansion card would be able to trigger EXT.DTACK independently of the glue logic.

I have now worked through the scenarios and these are my discoveries on the M5120 Portable: * Upgrade card set to 4MB or less: No perf degradation (no degradation after sleep) * Upgrade card set to 5MB or more: Perf degradation (worse after sleep) So it looks like for some reason or another...

It also depends on whether people want an update. Based on all my investigation, there's nothing wrong with the RAM card. It's performing exactly as it should. All these side effects of increased overhead due to memory management and the bug in CPU wait states are from things that are not...

I don't know if there's an easy way for you to flash the update. This is something I'd have to look into, because it's not friendly or convenient like an STM32 or Raspberry Pi Pico. This CPLD uses JTAG for flashing, which is a lot less common.

Overall it appears that any slowdown after a cold boot is probably due to system overhead with the memory manager. The strange behavior after sleep is because of a bug with the glue chip's wait states. My next step is to tweak the firmware again to increase available memory and see where the...

I created a "quick and dirty" test firmware for the CPLD. It reports as 3 megs of expansion (but provides 3.5mb because chip select logic is complicated). The Portable doesn't know what to do with half-meg increments and generally leaves it alone. The results? 2.08 CPU performance rating...

Ah, so it's the cpu glue which controls that. Is there a register or address reference available?