First Pixels — Hello World on the E-Ink Display

We got pixels. Real, physical, black-on-white pixels on the Waveshare 2.13" e-ink display, driven by C firmware on the Pico W. Phase 1's proof-of-life is alive.

The Moment

There's a specific feeling when hardware you've been researching and wiring actually does the thing. You flash the UF2, the Pico reboots, the BUSY pin goes low, and then — text appears on the display. No Python interpreter, no OS, no abstraction layers. Just C talking SPI to a display controller pushing pixels into electrophoretic ink.

The hello-world firmware is 106KB compiled. It initializes SPI1 at 4MHz, configures the SSD1680 display controller, clears the screen, and renders "HELLO DILDER" using the Waveshare paint library. Takes about 3 seconds for the full refresh. Partial refresh drops that to under a second.

What It Took to Get Here

More than you'd think. The Pico SDK's build system is CMake + Ninja, which is powerful but unforgiving if your environment isn't set up exactly right. On Arch Linux (my daily driver), the ARM cross-compiler is arm-none-eabi-gcc from the AUR, and the SDK needs PICO_SDK_PATH exported before CMake will even configure.

The wiring was straightforward — 8 jumper wires from the e-Paper HAT's side header to the Pico W's SPI1 pins. No level shifters needed since both run at 3.3V. The only gotcha: the display's BUSY pin is active-high during refresh, and you have to poll it before sending the next command or you'll corrupt the frame.

Pico W SPI1 → Waveshare 2.13" V3:
  GP11 (TX)  → DIN     GP10 (SCK) → CLK
  GP9  (CSn) → CS      GP8        → DC
  GP12       → RST     GP13       → BUSY
  3V3        → VCC     GND        → GND

The Serial Heartbeat

Before touching the display, I flashed hello-world-serial — a minimal firmware that blinks the onboard LED and prints "Heartbeat" over USB serial at 115200 baud. This verified the entire toolchain end-to-end: compiler, linker, UF2 generation, BOOTSEL flashing, and USB CDC enumeration.

Watching minicom print heartbeat messages while the LED blinks is boring. But it's the kind of boring that means everything downstream is going to work.

Flash Efficiency

The compiled hello_dilder.uf2 is 106KB. The Pico W has 2MB (2048KB) of flash. That's 5.2% used for a program that initializes the full SPI display stack and renders text. This confirmed what the hardware research suggested — we have enormous headroom for the actual pet firmware, quote databases, sprite data, and whatever else Phase 2 brings.

For comparison, MicroPython's firmware alone uses ~700KB before you write a single line of code. Going C-first was the right call.

What's Next

The display works. Serial works. The toolchain is solid. Now we need proper tooling — a setup CLI so others can replicate this environment, and a DevTool GUI for day-to-day development. That's the next post.

But right now? Right now we're staring at text on e-ink and it feels real.