Initial bare-metal foundation for nRF52840 PTT-FHSS

- Fully open toolchain: arm-none-eabi-gcc inside Podman/Docker container
- Platform-agnostic build via justfile (auto-detects podman vs docker)
- CMake + Ninja build system with arm-none-eabi toolchain file
- nRF52840 linker script and startup with full 64-entry vector table
- Register access via typed bitfield unions (include/regs.h)
- FHSS channel sequencer: AES-128-ECB PRNG over 40 channels (2402-2480 MHz)
- Low-power sleep via SYSTEM_ON WFI + GPIOTE wakeup on button press
- Vendor deps as shallow git submodules: nrfx, CMSIS_5, tiny-AES-c

.gitignore

@@ -0,0 +1 @@
+build/

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "vendor/nrfx"]
+	path = vendor/nrfx
+	url = https://github.com/NordicSemiconductor/nrfx.git
+[submodule "vendor/CMSIS_5"]
+	path = vendor/CMSIS_5
+	url = https://github.com/ARM-software/CMSIS_5.git
+[submodule "vendor/tiny-aes-c"]
+	path = vendor/tiny-aes-c
+	url = https://github.com/kokke/tiny-AES-c.git

CMakeLists.txt

@@ -0,0 +1,77 @@
+cmake_minimum_required(VERSION 3.22)
+
+# must be set before project()
+set(CMAKE_TOOLCHAIN_FILE "${CMAKE_SOURCE_DIR}/cmake/arm-none-eabi.cmake")
+
+project(ptt_fhss C ASM)
+
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD_REQUIRED ON)
+
+# ── sources ────────────────────────────────────────────────────────────────
+
+add_executable(firmware
+    src/startup.c
+    src/main.c
+    src/radio.c
+    src/fhss.c
+    src/power.c
+    vendor/tiny-aes-c/aes.c
+)
+
+# ── include paths ──────────────────────────────────────────────────────────
+
+target_include_directories(firmware PRIVATE
+    include
+    vendor/nrfx/mdk                    # nRF52840 device headers (nrf52840.h etc.)
+    vendor/CMSIS_5/CMSIS/Core/Include  # core_cm4.h, cmsis_gcc.h etc.
+    vendor/tiny-aes-c
+)
+
+# ── preprocessor defines ───────────────────────────────────────────────────
+
+target_compile_definitions(firmware PRIVATE
+    NRF52840_XXAA  # device variant required by nrfx/mdk headers
+)
+
+# ── compiler flags ─────────────────────────────────────────────────────────
+
+set(CPU_FLAGS
+    -mcpu=cortex-m4
+    -mthumb
+    -mfpu=fpv4-sp-d16
+    -mfloat-abi=hard
+)
+
+target_compile_options(firmware PRIVATE
+    ${CPU_FLAGS}
+    -Os
+    -ffunction-sections
+    -fdata-sections
+    -fno-exceptions
+    -Wall
+    -Wextra
+    -Werror
+)
+
+# ── linker ─────────────────────────────────────────────────────────────────
+
+target_link_options(firmware PRIVATE
+    ${CPU_FLAGS}
+    -T ${CMAKE_SOURCE_DIR}/link/nrf52840.ld
+    -Wl,--gc-sections
+    -Wl,--print-memory-usage
+    -nostartfiles
+    -specs=nano.specs
+    -specs=nosys.specs
+)
+
+# ── post-build: .hex + size report ────────────────────────────────────────
+
+add_custom_command(TARGET firmware POST_BUILD
+    COMMAND arm-none-eabi-objcopy
+            -O ihex $<TARGET_FILE:firmware>
+            ${CMAKE_BINARY_DIR}/firmware.hex
+    COMMAND arm-none-eabi-size $<TARGET_FILE:firmware>
+    VERBATIM
+)

Dockerfile

@@ -0,0 +1,11 @@
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        gcc-arm-none-eabi \
+        binutils-arm-none-eabi \
+        libnewlib-arm-none-eabi \
+        cmake \
+        ninja-build \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /src

README.md

@@ -0,0 +1,123 @@
+# ptt-fhss
+
+Bare-metal PTT (Push-to-Talk) firmware for the **Seeed XIAO BLE (nRF52840)** with
+frequency-hopping spread spectrum (FHSS) on the 2.4 GHz band.
+
+Designed to be low-power, hard to detect, and built with a fully open toolchain -
+no Zephyr, no Nordic SDK, no SoftDevice.
+
+## Hardware
+
+| Component | Part |
+|-----------|------|
+| Target | Seeed XIAO BLE (nRF52840) |
+| Programmer | RP2040 running DAPLink |
+
+## How it works
+
+### FHSS
+
+The radio hops across 40 channels (2402-2480 MHz, 2 MHz steps) every 2 ms.
+The hopping sequence is generated by AES-128-ECB keyed with a shared secret -
+both devices derive identical sequences independently without any synchronisation
+traffic. To an observer with an SDR the transmissions appear as short, scattered
+impulses with no identifiable pattern.
+
+### Low power
+
+The nRF52840 stays in SYSTEM_ON sleep (`WFI`) with the DC/DC converter active
+(~1.5 uA quiescent). A GPIOTE edge event on the PTT button wakes the CPU;
+the radio is active only during the burst.
+
+### Register access
+
+All hardware register writes use typed bitfield unions defined in `include/regs.h`
+rather than raw bit-shift expressions. The union layout is guaranteed correct with
+`arm-none-eabi-gcc` (LSB-first bitfields on Cortex-M).
+
+## Toolchain
+
+Everything that produces the binary runs inside a container. The host only needs
+tools that talk to hardware (pyocd) or manage the build (just).
+
+| Tool | Purpose | Install |
+|------|---------|---------|
+| podman or docker | Container runtime | distro package |
+| just | Task runner | `cargo install just` or distro package |
+| pyocd | Flash / debug via DAPLink | `pip install pyocd` |
+| git | Source control + submodules | distro package |
+
+Inside the container: `debian:bookworm-slim` + `gcc-arm-none-eabi` from apt +
+`cmake` + `ninja`.
+
+## Quick start
+
+```sh
+git clone <repo-url> ptt
+cd ptt
+git submodule update --init --depth=1
+
+just build    # build firmware.hex inside container
+just flash    # flash via DAPLink (host pyocd)
+```
+
+On first run `just build` pulls the container image and compiles. Subsequent
+builds reuse the cached image and only recompile changed files.
+
+## Tasks
+
+```
+just build       compile firmware inside the container
+just flash       build + flash via DAPLink
+just gdbserver   start pyocd GDB server on port 3333
+just clean       remove build/
+just clean-all   remove build/ and the container image
+```
+
+## Project structure
+
+```
+.
+|-- Dockerfile               container image (debian + arm-gcc from apt)
+|-- justfile                 build / flash / debug tasks
+|-- CMakeLists.txt
+|-- cmake/
+|   \-- arm-none-eabi.cmake  CMake toolchain file
+|-- link/
+|   \-- nrf52840.ld          linker script (no SoftDevice, Flash @ 0x00000000)
+|-- include/
+|   |-- regs.h               hardware register bitfield unions
+|   |-- radio.h
+|   |-- fhss.h
+|   \-- power.h
+|-- src/
+|   |-- startup.c            vector table (64 entries) + Reset_Handler
+|   |-- main.c
+|   |-- radio.c              RADIO peripheral driver (stub)
+|   |-- fhss.c               AES-ECB hopping sequence generator
+|   \-- power.c              DC/DC, GPIOTE wakeup, WFI sleep
+\-- vendor/
+    |-- nrfx/                Nordic HAL headers, pinned to v2.9.0 (includes mdk/)
+    |-- CMSIS_5/             ARM core headers (core_cm4.h etc.)
+    \-- tiny-aes-c/          Public domain AES-128 implementation
+```
+
+## Before first flash
+
+The XIAO BLE ships with a SoftDevice which occupies the start of Flash.
+Erase it before flashing bare-metal firmware:
+
+```sh
+pyocd erase --target nrf52840 --chip
+```
+
+## Status
+
+| Module | State |
+|--------|-------|
+| Startup / vector table | done |
+| Linker script | done |
+| Power management (sleep + wakeup) | done |
+| FHSS sequence generator | done |
+| RADIO driver | stub - TX loop not yet implemented |
+| Sync protocol | not started |

cmake/arm-none-eabi.cmake

@@ -0,0 +1,16 @@
+set(CMAKE_SYSTEM_NAME      Generic)
+set(CMAKE_SYSTEM_PROCESSOR arm)
+
+set(CMAKE_C_COMPILER   arm-none-eabi-gcc)
+set(CMAKE_CXX_COMPILER arm-none-eabi-g++)
+set(CMAKE_ASM_COMPILER arm-none-eabi-gcc)
+set(CMAKE_OBJCOPY      arm-none-eabi-objcopy)
+set(CMAKE_SIZE         arm-none-eabi-size)
+
+# prevent cmake from link-testing the compiler against the host
+set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
+# do not search host paths for libraries or headers
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

include/fhss.h

@@ -0,0 +1,6 @@
+#pragma once
+#include <stdint.h>
+
+void    fhss_init(void);
+uint8_t fhss_next_channel(void);   /* next channel from AES-ECB PRNG sequence */
+void    fhss_sync_tick(void);      /* call every FHSS_DWELL_MS ms */

include/power.h

@@ -0,0 +1,4 @@
+#pragma once
+
+void power_init(void);
+void power_sleep_until_button(void);   /* SYSTEM_ON WFI, woken by GPIOTE event */

include/radio.h

@@ -0,0 +1,7 @@
+#pragma once
+#include <stdint.h>
+
+void    radio_init(void);
+void    radio_set_channel(uint8_t ch);        /* 0-39, maps to 2402-2480 MHz */
+void    radio_tx(const uint8_t *data, uint8_t len);
+void    radio_tx_burst(void);                 /* TX with FHSS hopping */

include/regs.h

@@ -0,0 +1,90 @@
+#pragma once
+#include <stdint.h>
+
+/*
+ * Hardware register bitfield unions for nRF52840 peripherals.
+ * Layout is guaranteed correct only with arm-none-eabi-gcc (LSB-first bitfields).
+ * Bit ranges match nRF52840 Product Specification v1.7.
+ */
+
+/* GPIOTE */
+
+/* CONFIG[n]: channel configuration */
+typedef union {
+    struct {
+        uint32_t MODE     : 2;   /* [1:0]   0=Disabled  1=Event  3=Task */
+        uint32_t          : 6;   /* [7:2]   reserved */
+        uint32_t PSEL     : 5;   /* [12:8]  pin number within port */
+        uint32_t PORT     : 1;   /* [13]    0=Port0  1=Port1 */
+        uint32_t          : 2;   /* [15:14] reserved */
+        uint32_t POLARITY : 2;   /* [17:16] 0=None  1=LoToHi  2=HiToLo  3=Toggle */
+        uint32_t          : 2;   /* [19:18] reserved */
+        uint32_t OUTINIT  : 1;   /* [20]    initial output value for Task mode */
+        uint32_t          : 11;  /* [31:21] reserved */
+    } bit;
+    uint32_t reg;
+} gpiote_config_t;
+
+#define GPIOTE_MODE_DISABLED  0u
+#define GPIOTE_MODE_EVENT     1u
+#define GPIOTE_MODE_TASK      3u
+#define GPIOTE_POL_NONE       0u
+#define GPIOTE_POL_LOTOHI     1u
+#define GPIOTE_POL_HITOLO     2u
+#define GPIOTE_POL_TOGGLE     3u
+
+/* INTENSET / INTENCLR: interrupt enable */
+typedef union {
+    struct {
+        uint32_t IN0  : 1;   /* [0]    channel 0 input event */
+        uint32_t IN1  : 1;   /* [1]    channel 1 input event */
+        uint32_t IN2  : 1;   /* [2] */
+        uint32_t IN3  : 1;   /* [3] */
+        uint32_t IN4  : 1;   /* [4] */
+        uint32_t IN5  : 1;   /* [5] */
+        uint32_t IN6  : 1;   /* [6] */
+        uint32_t IN7  : 1;   /* [7] */
+        uint32_t      : 23;  /* [30:8]  reserved */
+        uint32_t PORT : 1;   /* [31]    PORT event */
+    } bit;
+    uint32_t reg;
+} gpiote_inten_t;
+
+/* RADIO */
+
+/* FREQUENCY: radio channel */
+typedef union {
+    struct {
+        uint32_t FREQUENCY : 7;   /* [6:0]  offset from base frequency in MHz */
+        uint32_t           : 1;   /* [7]    reserved */
+        uint32_t MAP       : 1;   /* [8]    0: base=2400 MHz  1: base=2360 MHz */
+        uint32_t           : 23;  /* [31:9] reserved */
+    } bit;
+    uint32_t reg;
+} radio_frequency_t;
+
+#define RADIO_MAP_DEFAULT 0u   /* channel n -> 2400+n MHz */
+#define RADIO_MAP_BLE     1u   /* channel n -> 2360+n MHz */
+
+/* TXPOWER: transmit power */
+typedef union {
+    struct {
+        int32_t TXPOWER : 8;   /* [7:0]  signed dBm: +8, +7, +6, +5, +4, +3, +2,
+                                          0, -4, -8, -12, -16, -20, -40 */
+        uint32_t        : 24;  /* [31:8] reserved */
+    } bit;
+    uint32_t reg;
+} radio_txpower_t;
+
+/* MODE: radio data rate and modulation */
+typedef union {
+    struct {
+        uint32_t MODE : 4;   /* [3:0]  0=NRF_1Mbit  1=NRF_2Mbit  4=BLE_1Mbit ... */
+        uint32_t      : 28;  /* [31:4] reserved */
+    } bit;
+    uint32_t reg;
+} radio_mode_t;
+
+#define RADIO_MODE_NRF_1MBIT  0u
+#define RADIO_MODE_NRF_2MBIT  1u
+#define RADIO_MODE_BLE_1MBIT  4u

justfile

@@ -0,0 +1,44 @@
+# variables
+image     := "ptt-builder"
+build_dir := "build"
+
+# podman takes priority over docker
+engine := `command -v podman 2>/dev/null \
+           || command -v docker 2>/dev/null \
+           || { echo "error: podman or docker required" >&2; exit 1; }`
+
+# user-namespace mapping: podman rootless vs docker
+user_ns := `command -v podman >/dev/null 2>&1 \
+            && echo "--userns=keep-id" \
+            || echo "--user $(id -u):$(id -g)"`
+
+# recipes
+# build container image (only rebuilt when Dockerfile changes)
+image-build:
+    {{engine}} build -t {{image}} .
+
+# compile firmware inside the container
+build: image-build
+    {{engine}} run --rm \
+        {{user_ns}} \
+        -v "{{justfile_directory()}}:/src:z" \
+        {{image}} \
+        sh -c "cmake -B /src/{{build_dir}} -G Ninja \
+                     -DCMAKE_BUILD_TYPE=MinSizeRel /src \
+               && ninja -C /src/{{build_dir}}"
+
+# flash firmware via pyocd on the host (requires USB / DAPLink)
+flash: build
+    pyocd flash --target nrf52840 {{build_dir}}/firmware.hex
+
+# start GDB server for debugging
+gdbserver:
+    pyocd gdbserver --target nrf52840 --port 3333
+
+# remove build artifacts
+clean:
+    rm -rf {{build_dir}}
+
+# remove build artifacts AND the container image
+clean-all: clean
+    {{engine}} rmi {{image}} 2>/dev/null || true

link/nrf52840.ld

@@ -0,0 +1,66 @@
+/*
+ * nRF52840  -  no SoftDevice
+ * Flash: 1 MB @ 0x00000000
+ * RAM:   256 KB @ 0x20000000
+ *
+ * Before first flash, erase the entire chip to remove any SoftDevice:
+ *   pyocd erase --target nrf52840 --chip
+ */
+
+MEMORY
+{
+    FLASH (rx)  : ORIGIN = 0x00000000, LENGTH = 1024K
+    RAM   (rwx) : ORIGIN = 0x20000000, LENGTH = 256K
+}
+
+/* stack grows downward from the top of RAM */
+_estack = ORIGIN(RAM) + LENGTH(RAM);
+
+ENTRY(Reset_Handler)
+
+SECTIONS
+{
+    /* vector table must be at the start of Flash */
+    .isr_vector :
+    {
+        KEEP(*(.isr_vector))
+        . = ALIGN(4);
+    } > FLASH
+
+    /* code and read-only data */
+    .text :
+    {
+        *(.text .text.*)
+        *(.rodata .rodata.*)
+        . = ALIGN(4);
+        _etext = .;
+    } > FLASH
+
+    /* load address of .data in Flash  -  Reset_Handler copies from here */
+    _sidata = LOADADDR(.data);
+
+    /* initialized variables: stored in Flash, run from RAM */
+    .data :
+    {
+        _sdata = .;
+        *(.data .data.*)
+        . = ALIGN(4);
+        _edata = .;
+    } > RAM AT > FLASH
+
+    /* zero-initialized variables: Reset_Handler clears this region */
+    .bss (NOLOAD) :
+    {
+        _sbss = .;
+        *(.bss .bss.*)
+        *(COMMON)
+        . = ALIGN(4);
+        _ebss = .;
+    } > RAM
+
+    /DISCARD/ :
+    {
+        *(.ARM.exidx*)
+        *(.gnu.linkonce.armexidx.*)
+    }
+}

src/fhss.c

@@ -0,0 +1,41 @@
+#include "fhss.h"
+#include <aes.h>
+
+#define FHSS_CHANNELS  40u
+#define FHSS_DWELL_MS   2u
+
+/* TODO: replace with a real shared secret before deployment */
+static const uint8_t shared_key[16] = {
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+};
+
+static uint32_t slot;
+
+void fhss_init(void)
+{
+    slot = 0u;
+}
+
+uint8_t fhss_next_channel(void)
+{
+    uint8_t block[16] = {0};
+    struct AES_ctx ctx;
+
+    /* encode slot counter big-endian into the AES input block */
+    block[0] = (uint8_t)(slot >> 24);
+    block[1] = (uint8_t)(slot >> 16);
+    block[2] = (uint8_t)(slot >>  8);
+    block[3] = (uint8_t)(slot      );
+
+    AES_init_ctx(&ctx, shared_key);
+    AES_ECB_encrypt(&ctx, block);   /* encrypts block in-place */
+
+    slot++;
+    return block[0] % FHSS_CHANNELS;
+}
+
+void fhss_sync_tick(void)
+{
+    slot++;
+}

src/main.c

@@ -0,0 +1,15 @@
+#include "radio.h"
+#include "fhss.h"
+#include "power.h"
+
+int main(void)
+{
+    power_init();
+    radio_init();
+    fhss_init();
+
+    while (1) {
+        power_sleep_until_button();
+        radio_tx_burst();
+    }
+}

src/power.c

@@ -0,0 +1,37 @@
+#include "power.h"
+#include "regs.h"
+#include <nrf52840.h>
+#include <cmsis_gcc.h>
+
+/* P0.02 on XIAO BLE  -  adjust to match your schematic */
+#define BUTTON_PIN  2u
+
+void power_init(void)
+{
+    /* DC/DC converter has lower quiescent current than the LDO */
+    NRF_POWER->DCDCEN = 1u;
+
+    NRF_GPIOTE->CONFIG[0] = (gpiote_config_t){
+        .bit = {
+            .MODE     = GPIOTE_MODE_EVENT,
+            .PSEL     = BUTTON_PIN,
+            .PORT     = 0u,
+            .POLARITY = GPIOTE_POL_LOTOHI,
+        }
+    }.reg;
+
+    NRF_GPIOTE->INTENSET = (gpiote_inten_t){ .bit.IN0 = 1u }.reg;
+
+    NVIC_EnableIRQ(GPIOTE_IRQn);
+}
+
+void power_sleep_until_button(void)
+{
+    NRF_POWER->TASKS_LOWPWR = 1u;
+    __WFI();
+}
+
+void GPIOTE_IRQHandler(void)
+{
+    NRF_GPIOTE->EVENTS_IN[0] = 0u;
+}

src/radio.c

@@ -0,0 +1,27 @@
+#include "radio.h"
+#include "fhss.h"
+#include "regs.h"
+#include <nrf52840.h>
+
+void radio_init(void)
+{
+    /* TODO: configure RADIO peripheral (MODE, PCNF0/1, BASE/PREFIX, CRC) */
+}
+
+void radio_set_channel(uint8_t ch)
+{
+    NRF_RADIO->FREQUENCY = (radio_frequency_t){
+        .bit = { .FREQUENCY = ch, .MAP = RADIO_MAP_DEFAULT }
+    }.reg;
+}
+
+void radio_tx(const uint8_t *data, uint8_t len)
+{
+    (void)data; (void)len;
+    /* TODO: load packet, enable TX, wait for END event, disable */
+}
+
+void radio_tx_burst(void)
+{
+    /* TODO: hop + TX loop driven by fhss_next_channel() */
+}

src/startup.c

@@ -0,0 +1,168 @@
+#include <stdint.h>
+
+/* linker script symbols */
+extern uint32_t _sidata;  /* load address of .data in Flash */
+extern uint32_t _sdata;   /* start of .data in RAM */
+extern uint32_t _edata;   /* end of .data in RAM */
+extern uint32_t _sbss;
+extern uint32_t _ebss;
+extern uint32_t _estack;  /* address equals initial SP value */
+
+extern int main(void);
+
+void Reset_Handler(void);
+
+static void __attribute__((used)) Default_Handler(void)
+{
+    while (1);
+}
+
+/* ARM Cortex-M4 core exceptions */
+void NMI_Handler(void)        __attribute__((weak, alias("Default_Handler")));
+void HardFault_Handler(void)  __attribute__((weak, alias("Default_Handler")));
+void MemManage_Handler(void)  __attribute__((weak, alias("Default_Handler")));
+void BusFault_Handler(void)   __attribute__((weak, alias("Default_Handler")));
+void UsageFault_Handler(void) __attribute__((weak, alias("Default_Handler")));
+void SVC_Handler(void)        __attribute__((weak, alias("Default_Handler")));
+void DebugMon_Handler(void)   __attribute__((weak, alias("Default_Handler")));
+void PendSV_Handler(void)     __attribute__((weak, alias("Default_Handler")));
+void SysTick_Handler(void)    __attribute__((weak, alias("Default_Handler")));
+
+/* nRF52840 peripheral IRQs (IRQ0-IRQ47) */
+void POWER_CLOCK_IRQHandler(void)                        __attribute__((weak, alias("Default_Handler")));
+void RADIO_IRQHandler(void)                              __attribute__((weak, alias("Default_Handler")));
+void UARTE0_UART0_IRQHandler(void)                       __attribute__((weak, alias("Default_Handler")));
+void SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler(void) __attribute__((weak, alias("Default_Handler")));
+void SPIM1_SPIS1_TWIM1_TWIS1_SPI1_TWI1_IRQHandler(void) __attribute__((weak, alias("Default_Handler")));
+void NFCT_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void GPIOTE_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void SAADC_IRQHandler(void)                              __attribute__((weak, alias("Default_Handler")));
+void TIMER0_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void TIMER1_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void TIMER2_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void RTC0_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void TEMP_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void RNG_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void ECB_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void CCM_AAR_IRQHandler(void)                            __attribute__((weak, alias("Default_Handler")));
+void WDT_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void RTC1_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void QDEC_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void COMP_LPCOMP_IRQHandler(void)                        __attribute__((weak, alias("Default_Handler")));
+void SWI0_EGU0_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void SWI1_EGU1_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void SWI2_EGU2_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void SWI3_EGU3_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void SWI4_EGU4_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void SWI5_EGU5_IRQHandler(void)                          __attribute__((weak, alias("Default_Handler")));
+void TIMER3_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void TIMER4_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void PWM0_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void PDM_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void MWU_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void PWM1_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void PWM2_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void SPIM2_SPIS2_SPI2_IRQHandler(void)                  __attribute__((weak, alias("Default_Handler")));
+void RTC2_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void I2S_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void FPU_IRQHandler(void)                                __attribute__((weak, alias("Default_Handler")));
+void USBD_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void UARTE1_IRQHandler(void)                             __attribute__((weak, alias("Default_Handler")));
+void QSPI_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void CRYPTOCELL_IRQHandler(void)                         __attribute__((weak, alias("Default_Handler")));
+void PWM3_IRQHandler(void)                               __attribute__((weak, alias("Default_Handler")));
+void SPIM3_IRQHandler(void)                              __attribute__((weak, alias("Default_Handler")));
+
+/* vector table: 64 entries (16 core + 48 IRQs) */
+
+typedef void (*vector_fn)(void);
+
+__attribute__((section(".isr_vector"), used))
+const vector_fn vectors[64] = {
+    /* 0  */ (vector_fn)&_estack,
+    /* 1  */ Reset_Handler,
+    /* 2  */ NMI_Handler,
+    /* 3  */ HardFault_Handler,
+    /* 4  */ MemManage_Handler,
+    /* 5  */ BusFault_Handler,
+    /* 6  */ UsageFault_Handler,
+    /* 7  */ 0,
+    /* 8  */ 0,
+    /* 9  */ 0,
+    /* 10 */ 0,
+    /* 11 */ SVC_Handler,
+    /* 12 */ DebugMon_Handler,
+    /* 13 */ 0,
+    /* 14 */ PendSV_Handler,
+    /* 15 */ SysTick_Handler,
+
+    /* IRQ0  */ POWER_CLOCK_IRQHandler,
+    /* IRQ1  */ RADIO_IRQHandler,
+    /* IRQ2  */ UARTE0_UART0_IRQHandler,
+    /* IRQ3  */ SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler,
+    /* IRQ4  */ SPIM1_SPIS1_TWIM1_TWIS1_SPI1_TWI1_IRQHandler,
+    /* IRQ5  */ NFCT_IRQHandler,
+    /* IRQ6  */ GPIOTE_IRQHandler,
+    /* IRQ7  */ SAADC_IRQHandler,
+    /* IRQ8  */ TIMER0_IRQHandler,
+    /* IRQ9  */ TIMER1_IRQHandler,
+    /* IRQ10 */ TIMER2_IRQHandler,
+    /* IRQ11 */ RTC0_IRQHandler,
+    /* IRQ12 */ TEMP_IRQHandler,
+    /* IRQ13 */ RNG_IRQHandler,
+    /* IRQ14 */ ECB_IRQHandler,
+    /* IRQ15 */ CCM_AAR_IRQHandler,
+    /* IRQ16 */ WDT_IRQHandler,
+    /* IRQ17 */ RTC1_IRQHandler,
+    /* IRQ18 */ QDEC_IRQHandler,
+    /* IRQ19 */ COMP_LPCOMP_IRQHandler,
+    /* IRQ20 */ SWI0_EGU0_IRQHandler,
+    /* IRQ21 */ SWI1_EGU1_IRQHandler,
+    /* IRQ22 */ SWI2_EGU2_IRQHandler,
+    /* IRQ23 */ SWI3_EGU3_IRQHandler,
+    /* IRQ24 */ SWI4_EGU4_IRQHandler,
+    /* IRQ25 */ SWI5_EGU5_IRQHandler,
+    /* IRQ26 */ TIMER3_IRQHandler,
+    /* IRQ27 */ TIMER4_IRQHandler,
+    /* IRQ28 */ PWM0_IRQHandler,
+    /* IRQ29 */ PDM_IRQHandler,
+    /* IRQ30 */ 0,  /* reserved */
+    /* IRQ31 */ 0,  /* reserved */
+    /* IRQ32 */ MWU_IRQHandler,
+    /* IRQ33 */ PWM1_IRQHandler,
+    /* IRQ34 */ PWM2_IRQHandler,
+    /* IRQ35 */ SPIM2_SPIS2_SPI2_IRQHandler,
+    /* IRQ36 */ RTC2_IRQHandler,
+    /* IRQ37 */ I2S_IRQHandler,
+    /* IRQ38 */ FPU_IRQHandler,
+    /* IRQ39 */ USBD_IRQHandler,
+    /* IRQ40 */ UARTE1_IRQHandler,
+    /* IRQ41 */ QSPI_IRQHandler,
+    /* IRQ42 */ CRYPTOCELL_IRQHandler,
+    /* IRQ43 */ 0,  /* reserved */
+    /* IRQ44 */ 0,  /* reserved */
+    /* IRQ45 */ PWM3_IRQHandler,
+    /* IRQ46 */ 0,  /* reserved */
+    /* IRQ47 */ SPIM3_IRQHandler,
+};
+
+/* Reset_Handler */
+
+void Reset_Handler(void)
+{
+    /* copy .data initializers from Flash to RAM */
+    uint32_t *src = &_sidata;
+    uint32_t *dst = &_sdata;
+    while (dst < &_edata) {
+        *dst++ = *src++;
+    }
+
+    /* zero .bss */
+    dst = &_sbss;
+    while (dst < &_ebss) {
+        *dst++ = 0u;
+    }
+
+    main();
+    while (1);
+}