After a long absence, the Mac ROM-inator Kit is back in stock at the BMOW store. The ROM-inator replaces the stock 64K or 128K of ROM in a compact Macintosh with a full 1 MB of flash memory. Once installed, the flash ROM’s contents can be updated from within the running Macintosh, allowing for a bootable ROM disk and crazy customization possibilities. It’s compatible with the Macintosh Plus, 512Ke, 512K, and 128K.

The kit includes preprogrammed flash chips with the following ROM changes as defaults. Any of them can be changed by updating the flash memory with a simple GUI tool.

• Startup beep is replaced by a glass “ping”
• Happy Mac icon is replaced by a Mac wearing sunglasses
• Pirate icon is displayed while waiting to load the ROM disk
• ROM disk image including System 6, utilities, and games
• 128K ROM code turns a Mac 128K or 512K into a 128Ke or 512Ke

 
Get Them While They Last

This will most likely be the final batch of Mac ROM-inator Kits, so if you’ve been wanting one, get it now! The ROM-inator is nice bit of technology, but when I put on my businessman hat I must admit it hasn’t been a great product. Stuffing the kits and pre-programming the ROMs is very time-intensive, and isn’t something I wish to continue doing. Instead, I’ve documented a “Make Your Own Kit” parts list and instructions for DIY builders. But for those who prefer a pre-packed kit, you can still get it while supplies last.

I’ve discovered a troubling problem with the Yellowstone disk controller for Apple II, and I’m unsure how to debug it. When it’s functioning as a Liron clone, Yellowstone isn’t playing nicely with other cards like a stock Disk II controller card. While booting from a Prodos 1.9 disk image using a Disk II controller in slot 6, Prodos crashes midway through booting if the Yellowstone card is present in slot 5. This happens even if there aren’t any drives connected to the Yellowstone card. It’s not 100% reproducible, but happens maybe 90% of the time. Yet everything works fine if I repeat the test with a real Liron controller card instead of the Yellowstone card. That means it’s my problem, and not the Liron designer’s.

I believe what’s happening is this: the Apple II scans the slots beginning with slot 7, and moving towards slot 1, looking for cards with a bootable ROM. It finds the Disk II card in slot 6, and jumps to its ROM code. That code loads sector 0 from the Prodos disk, displaying the splash screen shown in the photo. Then before Prodos has finished fully loading, the Apple II resumes the scan and jumps to the Yellowstone ROM code for slot 5. This code should look for attached Smartport devices, find that there aren’t any, and return. But somewhere during the execution of that ROM code, or during execution of the Prodos code just afterwards, something goes wrong. The Apple II stops and displays a system monitor prompt. Crash.

Where do I begin, with a bug like this? I don’t really know anything about the inner workings of Prodos, or even about the ROM code on the Yellowstone card, since I simply copied it verbatim from the Liron card without really studying it. That means I can’t easily figure out what the computer is trying to do at the moment it crashes.

My first guess is that I’m experiencing data bus contention, and the Yellowstone card is interfering with the Disk II card. The Disk II controller card and the Yellowstone card might both be attempting to put data on the bus at the same time, interfering with each other, and causing wrong values to be read from ROM code. But it’s hard to imagine how Yellowstone could be driving the bus at the wrong time. The output enable logic is pretty simple, and the Apple II already provides each slot with its own fully-decoded enable signals /DEVICE and /IOSELECT. There is a region of the Apple II address space that’s shared by all cards, and that uses a shared /IOSTROBE enable signal, but the Disk II card doesn’t use that address space.

My second guess is the reverse of the first: the presence of the Disk II card is somehow interfering with the Yellowstone card, exposing a flaw in the Yellowstone design that doesn’t appear when Yellowstone is the only card present. Maybe it’s somehow causing Yellowstone to malfunction. But I can’t really imagine what could cause that.

A third possibility is a problem caused by Prodos itself, rather than by the Disk II card. Maybe the first portion of Prodos alters some memory locations or sets some interrupt timers, or changes the system state in other ways that cause the Yellowstone boot ROM to fail. But it’s unclear why such an issue wouldn’t also affect a real Liron controller card in the same way.

A final possibility: maybe there’s a hardware problem with my Apple IIe, and there’s not enough juice to power two cards simultaneously, or the logic board is flakey. In the past on this same computer, I’ve occasionally seen similar crashes to the system monitor while booting Disk II software, long before Yellowstone even existed. Coincidence, or clue?

I’m scratching my head, trying to think what I could do to help troubleshoot this further, but I don’t have any great ideas.

BMOW’s Floppy Emu disk emulator for vintage Apple computers is back in stock. Get yours now at the BMOW store.