Crate embassy_stm32_hub75 

embassy-stm32-hub75

A no-std Rust driver for HUB75-style LED matrix panels on STM32 microcontrollers. HUB75 is a standard interface for driving large, bright, and colorful RGB LED displays, commonly used in digital signage and art installations.

This library uses an ISR-driven DMA refresh loop to continuously output framebuffer data to a GPIO port. A timer generates the pixel clock via PWM and triggers DMA transfers on each update event. Once the driver is initialised via hub75_define!’s init() function, rendering happens entirely in the background via DMA transfer-complete interrupts — no CPU involvement per pixel.

Double Buffering

The driver supports double-buffered operation via Hub75::swap(). The application writes to one framebuffer while the ISR renders from another, swapping atomically at frame boundaries.

8-bit Mode

In 8-bit mode, an external 74HC574-style latch handles the row address lines. This requires only 8 data pins: R1, G1, B1, R2, G2, B2, LATCH, and BLANK. The 8 pins must occupy either the lower byte (pins 0-7) or upper byte (pins 8-15) of a single GPIO port. Byte-width DMA writes to the corresponding ODR byte update only those 8 pins without disturbing the other half of the port.

16-bit Mode

In 16-bit mode, all 16 pins of a GPIO port are used. Half-word-width DMA writes the full ODR register on each clock cycle. Pin layout and bit assignments depend on the framebuffer implementation used.

Framebuffers

The hub75-framebuffer crate provides bitplane framebuffers that are strongly recommended for their memory efficiency. The plain 16-bit variant requires no external hardware beyond the panel itself. The latched 8-bit variant saves GPIO pins and cuts framebuffer memory nearly in half (one byte per pixel-clock instead of two), but requires an external 74HC574-style latch circuit (see the hub75-framebuffer README for the schematic). Both store one bit per pixel per plane and are output via DMA without format conversion.

Defining an Instance

Use the hub75_define! macro to create a driver module bound to specific timer and DMA channel peripherals:

use embassy_stm32::{bind_interrupts, dma, peripherals};
use embassy_stm32_hub75::hub75_define;

hub75_define!(hub75, embassy_stm32::peripherals::TIM2, embassy_stm32::peripherals::DMA1_CH1);

bind_interrupts!(struct Irqs {
    DMA1_CHANNEL1 =>
        dma::InterruptHandler<peripherals::DMA1_CH1>,
        hub75::Hub75DmaHandler;
});

let hub75 = hub75::init(
    p.TIM2, p.PA0, p.DMA1_CH1, Irqs, pins,
    Config::new().frequency(Hertz(6_000_000)),
    fb,
);

Crate Features

• defmt – enable defmt logging (forwards to embassy-stm32, hub75-framebuffer, and embedded-graphics)
• skip-black-pixels – skip writing black pixels to the framebuffer, leaving the bitplane data unchanged (forwards to hub75-framebuffer)
• invert-oe – invert the output-enable signal in the framebuffer (forwards to hub75-framebuffer)
• tail-closes-latch – append a tail word that closes the latch after data is shifted in; plain 16-bit mode only (forwards to hub75-framebuffer)
• blank-delay-{1,2,4,8} – insert 1/2/4/8 blank delay cycles after latching; plain 16-bit mode only (forwards to hub75-framebuffer)

Re-exports

pub use hub75_framebuffer as framebuffer;

Modules

dma

ISR-driven HUB75 timer+DMA panel driver.

Macros

hub75_define

Define a HUB75 driver instance with its own timer static and ISR handler.

Structs

Config

Driver configuration for pixel clock frequency (defaults to 10 MHz) and GPIO output speed (defaults to Medium).

Hertz

Hertz

Hub75Pins8

Pin configuration for a HUB75 panel with an external address latch.

Hub75Pins16

Pin configuration for a HUB75 panel using 16 data pins (full GPIO port width).

Enums

Hub75Error

Represents errors that can occur during HUB75 driver operations.

Speed

Speed setting for an output.

Traits

Hub75Pins

Trait implemented by HUB75 pin groups (8-bit or 16-bit).

Type Aliases

Color

The color type used by the HUB75 driver. Color type used in the framebuffer