BFE001
LED / low-pass filterA personal cartography of a mind that thinks in wireframes—from a ZX Spectrum in Dijon to the Amiga's memory-mapped hardware, and everything that wired itself in between.
Who I Am
I'm Mark Karpelès. I'm a systems thinker. I've spent most of my life building mental models of how things work—from the internals of a CPU down to transistors, from door handle mechanisms to distributed software architectures. Understanding the mechanism is the reward. Once a system becomes predictable, my brain moves on to the next unknown.
This site is named after $BFE001, a hardware register on the
Amiga's CIA 8520 chip. Writing bit 1 of that address toggled the
power LED and the audio low-pass filter. Some games used it to simulate the
muffled sound of passing through a tunnel. Of all the things I coded on the
Amiga, that single instruction—MOVE.b #$02,$BFE001—stuck
with me across decades. It felt like reaching into the machine and changing
its physical state with a line of code.
That feeling—of seeing inside a system, understanding its structure, and knowing exactly which wire to pull—is how I've experienced the world for as long as I can remember.
Why This Name
The Amiga mapped its hardware into the CPU's address space. Writing to a memory
address didn't just store a value—it changed the physical state of the
machine. $BFE001 was the address of CIA-A's Port A register,
which controlled the keyboard, the game port buttons, the power LED, and the
audio low-pass filter.
Games would toggle bit 1 to create effects like the muffled sound of a tunnel. On the Amiga 2000, it dimmed the power LED instead of fully turning it off. A single bit, a single address, and the machine changed its physical behavior.
That instruction—MOVE.b #$02,$BFE001—was one of the
first moments I felt the boundary between software and hardware dissolve.
It's the reason this site exists. It represents a way of thinking about
computers: not as black boxes, but as structures you can see into, understand,
and manipulate at every level.