Struct DmaFrameBuffer 

pub struct DmaFrameBuffer<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> { /* private fields */ }

DMA-compatible framebuffer for HUB75 LED panels with external latch circuit support.

This implementation is optimized for memory usage and external latch circuit support:

• Uses 8-bit entries instead of 16-bit
• Separates address and data words
• Supports the external latch circuit for row selection
• Implements the embedded-graphics DrawTarget trait

Type Parameters

• ROWS: Total number of rows in the panel
• COLS: Number of columns in the panel
• NROWS: Number of rows per scan (typically half of ROWS)
• BITS: Color depth (1-8 bits)
• FRAME_COUNT: Number of frames used for Binary Code Modulation

Helper Functions

Use these functions to compute the correct values:

• esp_hub75::compute_frame_count(BITS): Computes the required number of frames
• esp_hub75::compute_rows(ROWS): Computes the number of rows per scan

Memory Layout

The buffer is aligned to ensure efficient DMA transfers and contains:

• An array of frames, each containing the full panel data
• Each frame contains NROWS rows
• Each row contains both data and address words

Implementations

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

pub const fn new() -> Self

Create a new framebuffer with the given number of frames. The framebuffer is automatically formatted and ready to use.

Panics

With the esp32-ordering feature, panics if COLS is not divisible by 4 (the ESP32’s byte-order rearrangement requires column counts that are multiples of 4).

Example

use hub75_framebuffer::{latched::DmaFrameBuffer,compute_rows,compute_frame_count};

const ROWS: usize = 32;
const COLS: usize = 64;
const BITS: u8 = 3; // Color depth (8 brightness levels, 7 frames)
const NROWS: usize = compute_rows(ROWS); // Number of rows per scan
const FRAME_COUNT: usize = compute_frame_count(BITS); // Number of frames for BCM

let mut framebuffer = DmaFrameBuffer::<ROWS, COLS, NROWS, BITS, FRAME_COUNT>::new();
// Ready to use immediately

Memory placement (⚠️ large buffer)

This framebuffer is a large inline array of 8-bit words, one per pixel clock per frame, for (2^BITS)-1 frames. Even at 8-bit words the frame count grows exponentially with BITS, so the buffer quickly reaches tens of kilobytes. Never bind it to a task-local let — that places the whole buffer on the task stack and overflows it.

The framebuffer is mutable, so give it a 'static home that hands out &'static mut without unsafe — static mut is not an option. Use static_cell::StaticCell. See the crate-level Memory placement section for a worked example.

pub const fn bcm_chunk_count() -> usize

👎Deprecated since 0.11.0:

use BCM_SEQUENCE instead

Returns the number of BCM chunks in this framebuffer (always 1 for single-plane framebuffers — the entire buffer is one contiguous chunk).

pub const fn bcm_chunk_bytes() -> usize

👎Deprecated since 0.11.0:

use BCM_SEQUENCE instead

Returns the byte size of one BCM chunk (for single-plane framebuffers this equals the total DMA buffer size, since BCM weighting is baked in).

pub const fn format(&mut self)

Format the framebuffer, setting up all control bits and clearing pixel data. This method does a full format of all control bits and clears all pixel data. Normally you don’t need to call this as new() automatically formats the framebuffer.

Example

use hub75_framebuffer::{Color,latched::DmaFrameBuffer,compute_rows,compute_frame_count};

const ROWS: usize = 32;
const COLS: usize = 64;
const BITS: u8 = 3; // Color depth (8 brightness levels, 7 frames)
const NROWS: usize = compute_rows(ROWS); // Number of rows per scan
const FRAME_COUNT: usize = compute_frame_count(BITS); // Number of frames for BCM

let mut framebuffer = DmaFrameBuffer::<ROWS, COLS, NROWS, BITS, FRAME_COUNT>::new();
// framebuffer.format(); // Not needed - new() already calls this

pub fn erase(&mut self)

Erase pixel colors while preserving control bits. This is much faster than format() and is the typical way to clear the display.

Example

use hub75_framebuffer::{Color,latched::DmaFrameBuffer,compute_rows,compute_frame_count};

const ROWS: usize = 32;
const COLS: usize = 64;
const BITS: u8 = 3; // Color depth (8 brightness levels, 7 frames)
const NROWS: usize = compute_rows(ROWS); // Number of rows per scan
const FRAME_COUNT: usize = compute_frame_count(BITS); // Number of frames for BCM

let mut framebuffer = DmaFrameBuffer::<ROWS, COLS, NROWS, BITS, FRAME_COUNT>::new();
// ... draw some pixels ...
framebuffer.erase();

pub fn set_pixel(&mut self, p: Point, color: Color)

Set a pixel in the framebuffer.

Example

use hub75_framebuffer::{Color,latched::DmaFrameBuffer,compute_rows,compute_frame_count};
use embedded_graphics::prelude::*;

const ROWS: usize = 32;
const COLS: usize = 64;
const BITS: u8 = 3; // Color depth (8 brightness levels, 7 frames)
const NROWS: usize = compute_rows(ROWS); // Number of rows per scan
const FRAME_COUNT: usize = compute_frame_count(BITS); // Number of frames for BCM

let mut framebuffer = DmaFrameBuffer::<ROWS, COLS, NROWS, BITS, FRAME_COUNT>::new();
framebuffer.set_pixel(Point::new(10, 10), Color::RED);

Trait Implementations

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> Clone for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> Copy for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> Debug for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> Default for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn default() -> Self

Returns the “default value” for a type.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> DrawTarget for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

type Color = Rgb888

The pixel color type the targetted display supports.

type Error = !

Error type to return when a drawing operation fails.

fn draw_iter<I>(&mut self, pixels: I) -> Result<(), Self::Error>

where I: IntoIterator<Item = Pixel<Self::Color>>,

Draw individual pixels to the display without a defined order.

fn fill_contiguous<I>( &mut self, area: &Rectangle, colors: I, ) -> Result<(), Self::Error>

where I: IntoIterator<Item = Self::Color>,

Fill a given area with an iterator providing a contiguous stream of pixel colors.

fn fill_solid( &mut self, area: &Rectangle, color: Self::Color, ) -> Result<(), Self::Error>

Fill a given area with a solid color.

fn clear(&mut self, color: Self::Color) -> Result<(), Self::Error>

Fill the entire display with a solid color.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> FrameBuffer for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

const BCM_SEQUENCE: [BcmLenReps; 10]

Static (len, reps) of the segments in one sequence, in scan order.

const BCM_SEQUENCE_LEN: usize = 1

Number of BCM segments in one sequence, i.e. the number of meaningful entries in BCM_SEQUENCE.

const BCM_SEQUENCE_COUNT: usize = 1

Number of times the sequence repeats in one complete panel refresh: NROWS for row-major framebuffers (one sequence per row), 1 for frame-major and threshold framebuffers (the sequence covers the whole frame).

type Word = u8

The DMA word type used by this framebuffer (u8 for latched, u16 for direct-drive). Driver implementations can use this to enforce that pin configurations match the framebuffer at compile time.

fn bcm_segment_ptr(&self, index: usize) -> *const u8

Returns the byte pointer for the index-th BCM segment.

const BCM_SEGMENT_COUNT: usize = _

Total number of BCM segments streamed for one complete panel refresh (all rows, all planes).

const BCM_SEGMENTS_PER_GROUP: usize = 1

Number of consecutive segments that a driver may chain into a single DMA transfer. Must divide BCM_SEQUENCE_LEN: groups never straddle a sequence boundary.

fn bcm_segment_count(&self) -> usize

Total number of BCM segments streamed for one complete panel refresh.

fn bcm_segment(&self, index: usize) -> BcmSegment

Returns the index-th BCM segment.

fn bcm_segments_per_group(&self) -> usize

Number of consecutive segments that form one transfer group.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> FrameBufferOperations for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn erase(&mut self)

Erase pixel colors while preserving control bits. This is much faster than format() and is the typical way to clear the display.

fn set_pixel(&mut self, p: Point, color: Color)

Set a pixel in the framebuffer.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> MutableFrameBuffer for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> OriginDimensions for DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn size(&self) -> Size

Returns the size of the bounding box.

impl<const ROWS: usize, const COLS: usize, const NROWS: usize, const BITS: u8, const FRAME_COUNT: usize> OriginDimensions for &mut DmaFrameBuffer<ROWS, COLS, NROWS, BITS, FRAME_COUNT>

fn size(&self) -> Size

Returns the size of the bounding box.