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Drivers

Parallel LED Driver

Parlio (ESP32-P4)

Parallel LED Driver Technical Implementation

For end-user documentation, see Parallel LED Driver for ESP32-P4.

Architecture Overview:

The driver implements variable LEDs-per-pin support without intermediate buffers by padding during the transpose operation. Located in src/MoonLight/Nodes/Drivers/parlio.cpp with header parlio.h, called from D_ParallelLEDDriver.h.

Key Functions:

  1. show_parlio() (parlio.cpp:409-414): Entry point receiving compact channelsD buffer and leds_per_output[] array. Computes two global state variables:
  2. max_leds_per_output: Maximum across all pins

  3. first_index_per_output[16]: Cumulative offsets for random access into compact buffer

  4. create_transposed_led_output_optimized() (parlio.cpp:297): Main processing loop iterating 0..max_leds_per_output. Applies color remapping (offsetR/G/B/W) and brightness LUTs before calling transpose.

  5. transpose_32_slices() (parlio.cpp:181-183): Core padding mechanism using single conditional:

const uint8_t data_byte = pixel_in_pin < pixels_per_pin[pin]
    ? brightness_cache[input_buffer[component_idx]]  // Actual LED
    : 0;                                              // Padding (black)

When pixel_in_pin exceeds a pin's actual LED count, outputs zero, creating black padding pixels.

Data Flow: Input buffer remains compact (Σ(leds_per_pin[i]) × channels) → show_parlio() builds indexing structures → create_transposed_led_output_optimized() iterates to max → transpose_32_slices() conditionally reads/pads → DMA buffer written with uniform alignment → PARLIO hardware transmits.

Performance: Zero memory overhead for padding, O(1) offset lookup via first_index_per_output[], minimal branching in hot path. Chunking logic (parlio.cpp:480-505) handles large LED counts exceeding DMA limits.