Guys, if you make the right moves in Hnefatafl, a jötunn will appear that says, “Jonsi made this.”
Actually, vikings are credited with some of the earliest known name tag graffiti, so this would make a lot of sense.
Okay, I’m done ruining this thread…for now.
I some news that feels slightly embarrassing for me to share. Call it a plot twist, a technical foul, a mea culpa – whatever it is, it’s interesting and unexpected.
Now, I discovered this secret message using an emulator and was able to get to it just fine. Took less than a day to uncover it after I first peeked at the file.
Other people have been able to get it to work just fine on the original hardware, but with a catch: they either had to use either a flash cart or a fan-made multicart.
So far, nobody has been able to reproduce the easter egg on the actual original cartridge.
e5frog has 11 different copies of Spitfire, between carts and loose PCBs. He has dumped every single one of them, and verified that they all have the exact same ROM, bit for bit, as the one floating around the internet. He hasn’t been able to get it to work on those carts.
What gives?
Let’s look at some simplified pseudo-code for the code entry routine:
e5frog’s theory behind the issue has to do with the data counter.
From a programmer’s perspective, the data counter seems like it would be a normal CPU register. The F8 processor’s instruction set has several instructions that use this particular register: instructions to read and write the value of the counter itself, and instructions to use it as a pointer to read, modify, and write the stuff it’s pointing at. Seems simple enough.
The problem is (this is where things get weird) the data counter is technically not a CPU register. The data counter is actually located on the cart itself.
Here’s a simple diagram showing how the relationship between the CPU and a ROM would work in a sanely, elegantly designed system (not the Channel F):
The CPU shoves a number in the address wires, and the ROM pops out whatever number was at that address through some data wires.
The Channel F’s approach is a bit different:
Fairchild made chips called PSUs, short for “Program Storage Units”. These things contain normal ROMs inside of them that work just like in the previous picture. However, between the ROM and the CPU is a blob of digital logic and registers. The CPU communicates to this blob using a very strange bus protocol, and the blob uses that protocol to do things like figure out what ROM address to read. To help with this task, that blob has registers like the data counter and even the program counter.
(Why did they design it this way? To save on money. That ROMC bus only uses 5 pins, whereas a full address bus could have used 16 (fewer pins, lower cost). Likewise, having that logic blob be on a separate chip rather than on the CPU itself (like a sensible design) drove down the cost of the CPU (as well as giving their customers some sweet, sweet vendor lock-in).)
(Also, it bears mentioning that on some carts (particularly dev carts) that that logic blob was its own chip and the ROM chips were just normal ROM chips.)
Fortunately for the programmer, these hardware-level implementation details are practically irrelevant when actually, you know, programming.
Except, of course, when they are.
Spitfire is only 2 kilobytes in size. Accounting for the 2 kilobytes that the built-in games take up (those are on their own PSU, and no I don’t understand how that works), Spitfire’s PSU only really needs to be aware of 4 kilobytes of address space, and it only takes 12 bits to address 4 kilobytes.
e5frog’s theory is that the data counter in the actual Spitfire cart is only 12 bits wide, instead of being 16-bits like the F8’s documentation says. This makes some sense, because the game is small enough that those extra 4 bits would only be used to look at empty space, which is kind of pointless. Thus, removing those extra bits there would be a harmless cost-saving measure.
The problem with that, according to our theory, is that the data counter would never equal 0x1000. Even if you entered the passcode in correctly, the data counter would get to the last digit at 0x0FFF, would increase by one, and then would end up pointing to 0x0000 instead of 0x1000, and so the code never goes on to print the secret message – all because those upper bits don’t exist on the cart. And thus the easter egg exists, but it’s trapped.
(There may exist a revision of the cart where the egg is accessible, but I doubt it.)
The perverse thing about this all is that the easter egg was most likely accessible on the carts Michael Glass used during development. In fact, I’d wager that the message becoming inaccessible was completely unintentional – no executives clamping down on workers; no co-workers ratting each other out; no self-censorship – just an absent-minded technical oversight when moving from development to production (good thing that stuff like this never happens anymore).
Thanks to emulators and multicarts not implementing this obscure, cart-specific technical limitation, the easter egg finally became free.
What a story! The earliest known Easter egg trapped by 12 bits for decades until finally freed by a curious hobbyist. Great detective work.
The first easter egg is also a meta easter egg??
Holy shit, you were almost certainly the first person to see this on a screen since Michael last tested the game, that’s incredible
Best easter egg of all time imo, sorry flight simulator in excel
This must seriously be one of the most difficult to trigger easter eggs of all time. You have to invent emulators first
You’ve broken the seal that for long held back the terrible cyber curse, you’ve doomed us all
Wow, haven’t checked this thread in a while and now it’s legit blown up!
Also, let me just mention what a dashing man Michael K Glass was. It’s so cool to have a face to match the - now - videogame legend
The apple doesn’t fall far from the tree… @mkglass Jr isn’t too bad himself 
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Have you already considered looking at the other 3 videocarts (Videocart 1, 2 and 3) data by viewing them as raw, 1 bit-per-pixel images using YY-CHR?
I mean… while we’re at it. 
EDIT: I see RT-55J already posted something about this! ^^
Hello RT-55J sir.
I’m writing an article about Easter eggs for a Finnish retro gaming magazine Retro Rewind. This story will be featured in the article and I was wondering if I could use some of your screenshots in it?
Thanks.
Make sure they give you some money or a t-shirt in compensation.
based on the Energy of this person’s avatar I encourage @RT-55J to assent to this request
Feel free to use my screenshots and reference my posts, etc.
My PM box here is open if you have any questions.
Great, thank you very much!
oh hello there
Scrolled the comments and was relieved to find nobody mentioning this whew
Wow, Michael Glass. These pictures are from years before I met him.
Michael and Marsha moved in down the street from me when I was a kid, in the mid 80s.
Marsha’s son Shawn was my best friend for a bit there, and I was over at their house a lot.
I remember he had a full sized Pong machine in the living room, and I remember him telling us how much better the game design was on Fairchild games than the trash Atari stuff we wanted to play. That was probably the first and only time I saw a Fairchild machine in person.
I met April (I think that’s right? its been a long time…) a couple of times as well. Shawn and I watched Halloween II with her on TV. She was really nice to me.
Hi there… World_Eater LOL
Marsha was awesome, as were her boys. I was a little older than them and April.
Sadly, Marsha passed away a while ago, and April died 4 years ago – just a week or so before I found this thread. I have been in sporadic contact with Shawn via Facebook, but my most recent message to him has gone unread. Not sure what he’s up to these days.
I have been in talks with a guy in England who is working on a documentary about the Channel F, and will be featuring the easter egg and my father. If you would like to contribute any memories, let me know, and maybe I can put you in touch with him. If so, you can reach me at mglass@gmail.com, or on FB: “mkglass”
I did not know my father well, unfortunately. It’s nice to hear from someone who knew about him and our family. Hope to hear from you soon!
