NOTES¶

DMA + Double Buffer — Ping-Pong Buffer with DMA Offloading

DMA (Direct Memory Access) automatically transfers sensor data to memory — the CPU doesn't need to move every byte. Double buffering (ping-pong) ensures zero-gap acquisition.

Intuition¶

Why DMA is Fast¶

Normal: CPU reads sensor data byte by byte → executes instructions → occupies CPU cycles.

DMA: Configure DMA once → DMA controller reads SPI/I2C data into memory autonomously → CPU stays free to process data.

Double Buffer (Ping-Pong)¶

Two buckets A and B:

DMA fills A → A full → DMA switches to B → CPU processes A
DMA fills B → B full → DMA switches to A → CPU processes B

DMA and CPU work in parallel, never waiting. Zero-gap acquisition.

Data Flow¶

DMA transfer complete interrupt
    → Buffer A full → notify Consumer task
    → DMA auto-switches to Buffer B
    Consumer reads Buffer A and processes
    → Consumer finishes → waits for next interrupt

Notes¶

When to use DMA + Double Buffer?

Upgrade here when the Producer-Consumer ring buffer drops too many samples. DMA guarantees acquisition speed is never CPU-bound.

DMA requires HW support

ESP32-S3's SPI2/I2C controllers support DMA. Verify ADXL355 is connected to a DMA-capable peripheral interface.

Double buffer = 2 × buffer_size × 28 bytes

Two 512-sample buffers ≈ 28 KB. Twice the memory of Producer-Consumer, but much higher throughput.