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nRF54L15 Arduino core for XIAO nRF54L15 using a clean register-level implementation (no Zephyr/NCS runtime)

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Nrf54L15-Clean-Implementation

Open-source Arduino board package for Seeed XIAO nRF54L15 with a clean register-level implementation.

  • Core name: Nrf54L15-Clean-Implementation
  • Board: XIAO nRF54L15 (Nrf54L15-Clean-Implementation)
  • FQBN: nrf54l15clean:nrf54l15clean:xiao_nrf54l15
  • No Zephyr runtime dependency
  • No nRF Connect SDK runtime dependency

Why this repo exists

This repo is intentionally different from the Zephyr-based core:

  • Uses direct register programming for core + HAL behavior.
  • Ships as a normal Arduino Boards Manager package.
  • Does not require users to install large external SDKs to build/upload.

Boards Manager install

Add this URL to Arduino IDE / Arduino CLI Additional Boards Manager URLs:

https://raw.githubusercontent.com/lolren/NRF54L15-Clean-Arduino-core/main/package_nrf54l15clean_stable_index.json

If your IDE/CLI already cached an older index, remove cache and update indexes:

  • Linux: rm -f ~/.arduino15/package_nrf54l15clean_index.json ~/.arduino15/package_nrf54l15clean_stable_index.json
  • Then run: arduino-cli core update-index

Then install package Nrf54L15-Clean-Implementation and select board:

  • XIAO nRF54L15 (Nrf54L15-Clean-Implementation)

Linux CMSIS-DAP permissions (one-time)

If upload reports No connected debug probes but lsusb shows 2886:0066 Seeed Studio XIAO nrf54 CMSIS-DAP, add a udev rule:

cat <<'RULE' | sudo tee /etc/udev/rules.d/60-seeed-xiao-nrf54-cmsis-dap.rules >/dev/null
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="2886", ATTRS{idProduct}=="0066", MODE="0660", GROUP="plugdev", TAG+="uaccess"
SUBSYSTEM=="usb", ATTR{idVendor}=="2886", ATTR{idProduct}=="0066", MODE="0660", GROUP="plugdev", TAG+="uaccess"
RULE
sudo udevadm control --reload-rules
sudo udevadm trigger --attr-match=idVendor=2886 --attr-match=idProduct=0066

Pinout

XIAO nRF54L15 default pin routes

Default peripheral routes

Peripheral Default pins Notes
Wire (I2C primary) SDA=D4(P1.10), SCL=D5(P1.11) Sketch compatibility default
Wire1 (I2C secondary) SDA=D12(P0.04), SCL=D11(P0.03) Back-pad bus
SPI MOSI=D10(P2.02), MISO=D9(P2.04), SCK=D8(P2.01), SS=D2(P1.06) Runtime clock via SPISettings
Serial1 / Serial2 TX=D6(P2.08), RX=D7(P2.07) Serial2 is alias of Serial1
Serial USB bridge (default) Can be switched to header UART via Tools menu

Arduino pin map (Arduino -> MCU)

Arduino pin MCU pin ADC input Typical role
D0 / A0 P1.04 AIN0 GPIO / ADC
D1 / A1 P1.05 AIN1 GPIO / ADC
D2 / A2 P1.06 AIN2 GPIO / ADC / SS
D3 / A3 P1.07 AIN3 GPIO / ADC
D4 / A4 P1.10 N/A Wire SDA
D5 / A5 P1.11 AIN4 Wire SCL
D6 P2.08 N/A Serial1/2 TX
D7 P2.07 N/A Serial1/2 RX
D8 P2.01 N/A SPI SCK
D9 P2.04 N/A SPI MISO
D10 P2.02 N/A SPI MOSI
D11 P0.03 N/A Back pad / Wire1 SCL
D12 P0.04 N/A Back pad / Wire1 SDA
D13 P2.10 N/A Back pad GPIO
D14 P2.09 N/A Back pad GPIO
D15 P2.06 N/A Back pad GPIO
LED_BUILTIN (16) P2.00 N/A User LED (active-low)
PIN_BUTTON (17) P0.00 N/A User button (active-low)
PIN_SAMD11_RX (18) P1.09 N/A USB bridge route
PIN_SAMD11_TX (19) P1.08 N/A USB bridge route

Additional board-control nets exposed in HAL:

Function MCU pin Symbol
VBAT divider enable P1.15 kPinVbatEnable
VBAT ADC sense P1.14 kPinVbatSense / A7
RF switch control P2.05 kPinRfSwitchCtl

MCU pin map (MCU -> Arduino)

MCU pin Arduino alias
P0.00 PIN_BUTTON
P0.03 D11
P0.04 D12
P1.04 D0/A0
P1.05 D1/A1
P1.06 D2/A2
P1.07 D3/A3
P1.08 PIN_SAMD11_TX
P1.09 PIN_SAMD11_RX
P1.10 D4/A4
P1.11 D5/A5
P1.14 A7 / VBAT sense
P1.15 VBAT enable
P2.00 LED_BUILTIN
P2.01 D8
P2.02 D10
P2.04 D9
P2.05 RF switch control
P2.06 D15
P2.07 D7
P2.08 D6
P2.09 D14
P2.10 D13

Implemented Arduino core APIs

  • GPIO: pinMode, digitalRead, digitalWrite, attachInterrupt, detachInterrupt
  • ADC/PWM: analogRead, analogReadResolution(bits), analogWrite, analogWriteResolution
  • UART: Serial, Serial1, Serial2
  • I2C: Wire + Wire1, repeated-start, target/slave callbacks
  • SPI: transactions + runtime frequency/mode/order
  • Timing/power: millis, micros, delays, optional low-power idle profile

HAL blocks in bundled library

Library path:

  • hardware/nrf54l15clean/0.1.0/libraries/Nrf54L15-Clean-Implementation

Implemented blocks:

  • ClockControl, Gpio, Spim, Twim, Uarte
  • Saadc, Timer, Pwm, Gpiote
  • PowerManager, Grtc, TempSensor, Watchdog, Pdm
  • BleRadio (custom peripheral LL + ATT/GATT subset)
  • BoardControl (battery sense + antenna route control)

Board control helpers (battery + RF switch)

#include "nrf54l15_hal.h"
using namespace xiao_nrf54l15;

int32_t vbatMv = 0;
uint8_t vbatPct = 0;
BoardControl::sampleBatteryMilliVolts(&vbatMv);
BoardControl::sampleBatteryPercent(&vbatPct);

BoardControl::setAntennaPath(BoardAntennaPath::kCeramic);
BoardControl::setAntennaPath(BoardAntennaPath::kExternal);
BoardControl::setAntennaPath(BoardAntennaPath::kControlHighImpedance);

Important RF note:

  • kControlHighImpedance releases P2.05 drive; it does not power-gate the RF switch IC.

Tools menu options

  • Upload method: Auto / pyOCD / OpenOCD
  • CPU frequency: 64 MHz / 128 MHz
  • BLE support: On / Off
  • BLE TX power: -20, -8, 0, +8 dBm
  • BLE timing profile: Interop / Balanced low-power / Aggressive low-power
  • BLE trace: Off / On
  • Power profile: Balanced / Low power (WFI idle)
  • Peripheral auto-gating: Off / 2 ms / 200 us
  • Antenna route: Ceramic / External U.FL
  • Serial routing: USB bridge / Header UART

Example sketches

Core examples:

  • hardware/nrf54l15clean/0.1.0/examples/01.Basics/AnalogReadSerial/AnalogReadSerial.ino
  • hardware/nrf54l15clean/0.1.0/examples/03.Peripherals/PeripheralProbe/PeripheralProbe.ino
  • hardware/nrf54l15clean/0.1.0/examples/03.Peripherals/InterruptPwmApiProbe/InterruptPwmApiProbe.ino
  • hardware/nrf54l15clean/0.1.0/examples/03.Peripherals/WireRepeatedStartProbe/WireRepeatedStartProbe.ino
  • hardware/nrf54l15clean/0.1.0/examples/03.Peripherals/WireTargetResponder/WireTargetResponder.ino

Library examples (HAL + BLE + power):

  • .../examples/BoardBatteryAntennaBusControl/BoardBatteryAntennaBusControl.ino
  • .../examples/InterruptWatchdogLowPower/InterruptWatchdogLowPower.ino
  • .../examples/BleAdvertiser/BleAdvertiser.ino
  • .../examples/BlePassiveScanner/BlePassiveScanner.ino
  • .../examples/BleActiveScanner/BleActiveScanner.ino
  • .../examples/BleConnectionPeripheral/BleConnectionPeripheral.ino
  • .../examples/BleGattBasicPeripheral/BleGattBasicPeripheral.ino
  • .../examples/BleCustomGattRuntime/BleCustomGattRuntime.ino
  • .../examples/BleBatteryNotifyPeripheral/BleBatteryNotifyPeripheral.ino
  • .../examples/BlePairingEncryptionStatus/BlePairingEncryptionStatus.ino
  • .../examples/BleBondPersistenceProbe/BleBondPersistenceProbe.ino
  • .../examples/BleConnectionTimingMetrics/BleConnectionTimingMetrics.ino

BLE status (current)

Validated and stable with host adapter + hardware:

  • Advertising
  • Passive scanning
  • Active scanning (SCAN_REQ / SCAN_RSP)
  • Connect/disconnect
  • GATT discovery/read
  • Battery notify CCCD flow

Current gap (tracked):

  • Pairing/bond persistence is still partial.
    • Successful Paired: yes / Bonded: yes outcomes are observed.
    • Repeated runs are still unstable due intermittent auth timeouts and Intel host-controller crash artifacts (Hardware Error 0x0c).

Channel sounding status:

  • BLE channel sounding / AoA/AoD style feature parity is not implemented yet in this clean core.
  • It is tracked as advanced future work due significant PHY + timing + controller complexity.

Validation artifacts

  • FEATURE_PARITY.md
  • TODO.md
  • POWER_PROFILE_MEASUREMENTS.md
  • docs/BLE_CLI_MATRIX_SUMMARY.md
  • docs/BLE_REGRESSION_RUNBOOK.md
  • docs/BUG_TRACKER.md
  • scripts/ble_cli_matrix.sh
  • scripts/ble_pair_bond_regression.sh

Local development workflow

Use one of:

  • ~/Arduino/hardware/... sketchbook override (active development)
  • ~/.arduino15/packages/... package-layout override

Example compile:

arduino-cli compile --fqbn nrf54l15clean:nrf54l15clean:xiao_nrf54l15 \
  hardware/nrf54l15clean/0.1.0/examples/03.Peripherals/InterruptPwmApiProbe/InterruptPwmApiProbe.ino

Example BLE matrix run:

bash scripts/ble_cli_matrix.sh --port /dev/ttyACM0 --sudo

Example pair/bond regression run:

bash scripts/ble_pair_bond_regression.sh --port /dev/ttyACM0 --sudo --attempts 10 --mode pair-bond

Example bonded reconnect regression run:

bash scripts/ble_pair_bond_regression.sh --port /dev/ttyACM0 --sudo --attempts 5 --mode bonded-reconnect --example BleBondPersistenceProbe

If multiple host adapters are present:

bash scripts/ble_pair_bond_regression.sh --sudo --controller AA:BB:CC:DD:EE:FF --btmon-iface hci1

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nRF54L15 Arduino core for XIAO nRF54L15 using a clean register-level implementation (no Zephyr/NCS runtime)

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arduino xiao clean-room nrf54l15 no-zephyr

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Nrf54L15-Clean-Implementation v0.1.0 Latest
Feb 22, 2026

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