WonderSwan v5.2: Color Only?

[Flavor]

Yes, I can elaborate. I can't get a whole lot of time for this sort of thing on the weekends, but I wanted to give you a quick workaround at the time.

Actually, when we say "v5.1" or "v5.2" on the circuit board, that's _just_ the board. In fact, the changes between those versions are inconsequential.

The change that matters here is the switch from a nvSRAM chip ("CY14B104LA" made by Cypress) to a MRAM chip ("MR2A08ACYS35" made by Everspin). All of Everspin's documentation shows the part as a direct drop-in replacement for the Cypress chip. We should be able to use them interchangeably according to their documentation. The Everspin chips are better for a handfull of reasons, so we bought some, tested them, and implemented them. In fact, some "v5.1" boards have the Everspin chip on them.

After we shipped this most recent batch of WS Flash Masta carts, we found out that they have bootup problems on the B&W Monochrome Wonderswan. The "problem" is actually complex, but it has to do with the power supply boost conversion on the B&W WS. We've been researching this for the past week or two.

As you know, the WS uses a single AA (1.5v) battery. The WS boosts this voltage to 3.3v. The WS Color and SwanCrystal have different boost circuitry than the B&W. Presumably, Bandai realized that improving this section of the system was needed, so they "fixed" it in the newer models. Also, the B&W model's design relies more on larger electrolytic capacitors. If you know anything about old electronics and video game hardware, you know that electrolytic caps get worse over time. That may play into this.

When the Color WS models boot up, they somewhat instantly go from 0 to 3.3v for the cartridge's power supply.

When the B&W WS boots up, it "kinda slowly" gives the cartridge voltage that ramps up over time. (Slowly is like a half second when using the Everspin chip.)

The Everspin chip reacts poorly to this interim voltage, and it causes a (very temporary) extra draw on the AA battery. If this is powered by something else that can supply more power, the system will boot up fine.

The reason that the "swap trick" works is that they system is already powered up, and swapping cartridges will supply the 3.3v "instantly" instead of during system power-up.

The Cypress chip doesn't exhibit this behavior. After a bunch of research and data gathering, we reached out to Everspin's technical support. They have been trying to help us, but they seem somewhat baffled themselves. They want to blame the power supply (the WS itself), but the fact remains that their chip is behaving differently than the Cypress chip that they claim to be a replacement for.

All of this is worsened by two things for us.
1) We've shipped a batch+ of these carts with that chip.
2) We've already re-ordered more of these chips for future batches.

So, we'd like to come up with a workaround, but we haven't found anything that can be fixed with a firmware update or anything like that. We did find a workaround to make the cart boot up, but it's not something that an end user could implement.

I am currently waiting for a response (that may turn into further conversation) with Everspin. I really hope we can get that chip working. Until we know more, I can't give any sort of new workaround, fix, update, or even guesses for the solution.