DMA-friendly framebuffer implementations for driving HUB75 RGB LED matrix panels with Rust. The crate focuses on performance, correct timing, and ergonomic drawing by integrating tightly with the embedded-graphics ecosystem.
A HUB75 panel behaves like a long daisy-chained shift-register:
CLK.OE HIGH), sets the address lines A–E, and produces a short pulse on LAT to latch the freshly-shifted data into the LED drivers.OE goes LOW again and the row pair lights up while the next one is already being shifted.Color depth is achieved with Binary/Bit-Angle Code Modulation (BCM): lower bit-planes are shown for shorter times, higher ones for longer, yielding 2^n intensity levels per channel while keeping peak currents low.
If you want a deeper explanation, have a look inside src/lib.rs — the crate documentation contains an extensive primer.
plain none 16 bit (14 used) high Simplest, wires exactly like a standard HUB75 matrix. latched external latch gate (see below) 8 bit ×½ of plain Lower memory footprint, but needs a tiny glue-logic board.
tiling::TiledFrameBuffer to drive several HUB75 panels as one large display.ChainTopRightDown and any of the framebuffers above (plain or latched).embedded-graphics canvas, so a 3 × 3 stack of 64 × 32 panels simply looks like a 192 × 96 screen while all coordinate translation happens transparently.The latched implementation assumes a small external circuit that holds the row address while gating the pixel clock. A typical solution uses a 74xx373 latch along with a few NAND gates:
The latch IC stores the address bits whilst one NAND gate blocks the CLK signal during the latch interval. The remaining spare gate can be employed to combine a global PWM signal with OE for fine-grained brightness control as shown.
Add the dependency to your Cargo.toml:
[dependencies] hub75-framebuffer = "0.4.2"
use hub75_framebuffer::{compute_frame_count, compute_rows};
use hub75_framebuffer::latched::DmaFrameBuffer;
// or ::plain::DmaFrameBuffer
const ROWS: usize = 32; // panel height
const COLS: usize = 64; // panel width
const BITS: u8 = 3; // colour depth ⇒ 7 BCM frames
const NROWS: usize = compute_rows(ROWS); // 16
const FRAME_COUNT:usize = compute_frame_count(BITS); // (1<<BITS)-1 = 7
// Create a framebuffer (already initialized/cleared)
let mut framebuffer = DmaFrameBuffer::<ROWS, COLS, NROWS, BITS, FRAME_COUNT>
::new();
You can now draw using any embedded-graphics primitive:
use embedded_graphics::prelude::*;
use embedded_graphics::primitives::{Circle, Rectangle, PrimitiveStyle};
use hub75_framebuffer::Color;
Rectangle::new(Point::new(0, 0), Size::new(COLS as u32, ROWS as u32))
.into_styled(PrimitiveStyle::with_fill(Color::BLACK))
.draw(&mut framebuffer)
.unwrap();
Circle::new(Point::new(20, 10), 8)
.into_styled(PrimitiveStyle::with_fill(Color::GREEN))
.draw(&mut framebuffer)
.unwrap();
Finally hand the raw DMA buffer off to your MCU's parallel peripheral.
esp-hal-dma (required when using esp-hal)
Required when using the esp-hal crate for ESP32 development. This feature switches the ReadBuffer trait implementation from embedded-dma to esp-hal::dma. If you're targeting ESP32 devices with esp-hal, you must enable this feature for DMA compatibility.
[dependencies]
hub75-framebuffer = { version = "0.4.2", features = ["esp-hal-dma"] }esp32-ordering (required for original ESP32 only)
Required when targeting the original ESP32 chip (not ESP32-S3 or other variants). This feature adjusts byte ordering to accommodate the quirky requirements of the ESP32's I²S peripheral in 8-bit and 16-bit modes. Other ESP32 variants (S2, S3, C3, etc.) do not need this feature.
[dependencies]
hub75-framebuffer = { version = "0.4.2", features = ["esp32-ordering"] }
Skip drawing black pixels for performance boost in UI applications. When enabled, calls to set_pixel() with Color::BLACK return early without writing to the framebuffer, assuming the framebuffer was already cleared.
Implement the defmt::Format trait so framebuffer types can be logged with the defmt ecosystem.
Embed documentation images when building docs on docs.rs. Not needed for normal usage.
Enable features in your Cargo.toml:
[dependencies]
hub75-framebuffer = { version = "0.4.2",
features = ["esp-hal-dma", "esp32-ordering"] }
All logic including bitfields, address mapping, brightness modulation and the embedded-graphics integration is covered by a comprehensive test-suite (≈ 300 tests).
Licensed under either of
at your option.
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