src/platforms/arm/nrf52/README.md
Nordic nRF52 family support.
The maintained backend targets the Adafruit nRF52 / Bluefruit Arduino BSP used by FastLED CI. That BSP provides the Nordic SDK headers, FreeRTOS integration, SoftDevice support, PWM EasyDMA, and SPIM HAL APIs this backend includes. Arduino mbed OS nRF52 boards such as Arduino Nano 33 BLE and Nano 33 BLE Sense are not supported by this backend today.
Clocked chipsets such as APA102, SK9822, and DotStar use the nRF52 SPIM
peripheral. DATA_RATE_MHZ() and DATA_RATE_KHZ() are honored by selecting
the fastest standard nRF52 SPIM rate that does not exceed the requested rate:
125 kHz, 250 kHz, 500 kHz, 1 MHz, 2 MHz, 4 MHz, or 8 MHz. The default
FASTLED_NRF52_SPIM is NRF_SPIM0, so requests above 8 MHz are clamped to
8 MHz. SPIM3 on nRF52840 can run faster, but this backend does not assume
SPIM3 because most board pin maps and sketches use SPIM0 by default.
WS2812/SK6812-style chipsets use PWM EasyDMA sequence playback. The current
clockless path uses one PWM arbiter instance by default and a static sequence
buffer sized by FASTLED_NRF52_MAXIMUM_PIXELS_PER_STRING (default 144). BLE
SoftDevice activity, RAM pressure, and multiple independent clockless strips
can make large SK6812/WS2812 installations unreliable on nRF52. For BLE-heavy
applications, prefer clocked LEDs such as APA102/SK9822/DotStar, reduce the
number of clockless strips, or use a single shorter clockless output.
WS2812/SK6812 LEDs also do not expose a separate update/latch signal. FastLED
sends the pixel waveform and then leaves the data line idle for the reset time.
If an application needs precisely scheduled visual updates independent of data
transfer time, use a clocked LED chipset or schedule the start of show() so
the protocol reset interval lands at the desired update time.
fastled_arm_nrf52.h: Aggregator; includes pin/SPI/clockless and sysdefs.fastpin_arm_nrf52.h, fastpin_arm_nrf52_variants.h: Pin helpers/variants.fastspi_arm_nrf52.h: SPI backend.clockless_arm_nrf52.h: Clockless driver.arbiter_nrf52.h: PWM arbitration utility (selects/guards PWM instances for drivers).led_sysdefs_arm_nrf52.h: System defines for nRF52.Notes:
CLOCKLESS_FREQUENCY definition in many setups; PWM resources may be shared and must be arbitrated.arbiter_nrf52.h exposes a small API to acquire/release PWM instances safely across users; ensure ISR handlers are lightweight.FASTLED_USE_PROGMEM: Default 0 (flat memory model).FASTLED_ALLOW_INTERRUPTS: Default 1.FASTLED_ALL_PINS_HARDWARE_SPI: Enabled by default unless forcing software SPI.FASTLED_NRF52_SPIM: Select SPIM instance (e.g., NRF_SPIM0).FASTLED_NRF52_ENABLE_PWM_INSTANCE0: Enable PWM instance used by clockless.FASTLED_NRF52_NEVER_INLINE: Controls inlining attribute via FASTLED_NRF52_INLINE_ATTRIBUTE.FASTLED_NRF52_MAXIMUM_PIXELS_PER_STRING: Limit pixels per string in PWM-encoded path (default 144).FASTLED_NRF52_PWM_ID: Select PWM instance index used.FASTLED_NRF52_SUPPRESS_UNTESTED_BOARD_WARNING: Suppress pin-map warnings for unverified boards.FASTLED_NRF52_ALLOW_NFC_PINS: Re-enable P0.09 / P0.10 (NFC1/NFC2) as valid FastLED output pins on every nRF52840 variant block (SuperMini, nice!nano v2, nRFMicro, XIAO nRF52840, XIAO nRF52840 Sense). Defining this macro is necessary but not sufficient: you also need either CONFIG_NFCT_PINS_AS_GPIOS=1 in the BSP/build flags, or a call to NFC_PINS_AS_GPIO() at boot (Adafruit nRF52 core helper).FASTLED_NRF52_ALLOW_USR_LED: Re-enable on-board user-LED pins (P0.15 SuperMini/nice!nano v2, P1.10 nRFMicro, and the XIAO RGB LEDs at P0.26/P0.06/P0.30) as valid FastLED output pins. Be careful: defining this risks a clash with any sketch (or BSP background task) that calls digitalWrite(LED_BUILTIN, ...) on the same pin.EXT_VCC enable pins (P0.13 SuperMini/nice!nano v2, P1.09 nRFMicro), VBAT-sense pins, HICHG/~CHG, and QSPI flash pins remain invalid unconditionally — toggling EXT_VCC mid-show() browns out the regulator, and the others are not safe for FastLED output.
Define before including FastLED.h.