eink-api/README.md

eInk API for Raspberry Pi Pico

This firmware drives a Waveshare 4.2" e-Paper display from a Raspberry Pi Pico / Pico W. It launches the e-paper driver on core 1 while core 0 acts as a simple serial command processor, giving you an interactive API for drawing primitives, text, and editor-mode logs over USB.

Features

• Lightweight C implementation built on the official Pico SDK and Waveshare e-Paper drivers.
• Core 1 renders directly to a framebuffer and updates the display with both full and partial refreshes.
• Serial command queue exposes operations such as clearing, drawing geometry, writing text, and entering an editor mode.
• Automatic display shutdown after 30 seconds of inactivity to preserve the panel.

Requirements

• Raspberry Pi Pico or Pico W (project sets PICO_BOARD to pico_w).
• Waveshare 4.2" e-Paper V2 display, wired to SPI + compatible GPIOs defined in DEV_Config.h.
• Pico SDK (2.2.0) installed and available via PICO_SDK_PATH.
• cmake, ninja, and picotool (or the Pico toolchain) for flashing.

Building

# configure the build
cmake -S . -B build

# build the UF2 image
cmake --build build

After building, flash the firmware to your Pico (e.g. by copying build/eink_api.uf2 to the Pico's mass storage device or using picotool load build/eink_api.uf2).

Usage

1. Open a serial terminal (115200 baud) over the Pico's USB CDC interface.
2. Type commands followed by Enter. The firmware echoes the command buffer and executes the operation on core 1.
3. Most commands require the display to be initialized (init). The device automatically turns off the screen after ~30 seconds of inactivity, so send another command to revive it.
4. If editor mode is enabled, keystrokes are batched and rendered directly on the display until inactivity ends the mode.

Supported Commands

Command	Description
init	Initializes the e-Paper panel and allocates the framebuffer.
clear	Clears the current framebuffer to white (requires display on).
display	Pushes the framebuffer to the panel (requires display on).
draw_test	Draws a hard-coded Waveshare demo pattern.
draw_text x y text	Writes text at (x,y) using the current font.
draw_point x y	Draws a black point at the given coordinates.
draw_line x1 y1 x2 y2	Draws a black line between two points.
draw_rectangle x1 y1 x2 y2	Draws an empty rectangle.
draw_circle x y r	Draws an empty circle with radius r.
draw_num x y num	Draws num using the default numeric font.
set_pixel x y color	Sets a single pixel to color (0=white, 1=black).
close	Sends the panel to deep sleep and frees the framebuffer.
editor	Enables editor mode; text typed is rendered live on-screen until inactivity.

Notes

• The project imports the Waveshare e-Paper libraries from Pico_ePaper_Code/c/lib/* for configuration, fonts, GUI primitives, and the panel driver.
• USB serial I/O is enabled (pico_enable_stdio_usb), while UART stdio is disabled to avoid conflicts (pico_enable_stdio_uart set to 0).
• The firmware allocates the framebuffer via malloc and frees it when the display goes to sleep; avoid running out of heap on severely constrained Pico builds.
• Editor-mode inactivity is 10 seconds before automatically exiting back to command mode.