Debugging Guide¶

This comprehensive guide covers debugging techniques, tools, and best practices for Nexus embedded applications.

Overview ¶

Debugging embedded systems presents unique challenges compared to desktop applications. This guide provides strategies and tools for effective debugging on Nexus.

Key Topics:

Debug tools and setup
Printf-style debugging
Hardware debuggers (GDB, OpenOCD)
Log framework for debugging
Common debugging scenarios
Platform-specific debugging
Performance profiling
Memory debugging

Debug Build Configuration ¶

Enabling Debug Symbols ¶

CMake Configuration:

# Debug build with symbols
cmake -B build -DCMAKE_BUILD_TYPE=Debug

# Release with debug info
cmake -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo

Compiler Flags:

Debug builds automatically include:

-g3 - Maximum debug information
-Og - Optimize for debugging
DEBUG - Debug macro defined
No optimization that hinders debugging

Kconfig Options:

# Enable debug features
CONFIG_DEBUG=y
CONFIG_DEBUG_ASSERTIONS=y
CONFIG_DEBUG_VERBOSE=y

# Enable framework debug output
CONFIG_FRAMEWORK_LOG=y
CONFIG_LOG_LEVEL_DEBUG=y

Optimization Levels ¶

Different optimization levels affect debuggability:

Build Type	Optimization	Debuggability
Debug	`-Og`	Excellent
RelWithDebInfo	`-O2 -g`	Good
Release	`-O2`	Limited
MinSizeRel	`-Os`	Limited

Printf-Style Debugging ¶

Using Log Framework ¶

The Log framework is the primary debugging tool:

#define LOG_MODULE "mymodule"
#include "log/log.h"

void my_function(int value)
{
    LOG_DEBUG("Entering my_function with value=%d", value);

    if (value < 0) {
        LOG_WARN("Negative value detected: %d", value);
    }

    /* Function logic */

    LOG_DEBUG("Exiting my_function");
}

Advantages:

Minimal performance impact
Works on all platforms
Supports multiple backends
Module-level filtering
Timestamp information

Best Practices:

Use appropriate log levels
Include context in messages
Log function entry/exit for complex flows
Log error conditions with details
Use module names for filtering

Debug Macros ¶

Conditional Debug Code:

#ifdef DEBUG
static void dump_buffer(const uint8_t* buf, size_t len)
{
    for (size_t i = 0; i < len; i++) {
        LOG_DEBUG("buf[%zu] = 0x%02X", i, buf[i]);
    }
}
#endif

void process_data(const uint8_t* data, size_t len)
{
#ifdef DEBUG
    dump_buffer(data, len);
#endif
    /* Process data */
}

Assertions:

#include "hal/nx_assert.h"

void set_speed(uint32_t speed)
{
    /* Assert valid range */
    NX_ASSERT(speed >= MIN_SPEED && speed <= MAX_SPEED);

    /* Set speed */
}

UART Debug Output ¶

Setup UART for Debug:

/* Initialize UART for debug output */
nx_uart_config_t uart_cfg = {
    .baudrate = 115200,
    .word_length = 8,
    .stop_bits = 1,
    .parity = 0,
};

nx_uart_t* debug_uart = nx_factory_uart_with_config(0, &uart_cfg);

/* Register UART backend for logging */
log_backend_t* uart_backend = log_backend_uart_create(debug_uart);
log_backend_register(uart_backend);

Connect Serial Terminal:

# Linux/macOS
screen /dev/ttyUSB0 115200

# Windows (PowerShell)
# Use PuTTY, TeraTerm, or similar

Hardware Debugger Setup ¶

GDB + OpenOCD (STM32)¶

Install Tools:

# Ubuntu/Debian
sudo apt-get install gdb-multiarch openocd

# macOS
brew install gdb openocd

# Windows
# Download from ARM website and OpenOCD releases

OpenOCD Configuration:

Create openocd.cfg:

# STM32F4 Discovery
source [find interface/stlink.cfg]
source [find target/stm32f4x.cfg]

# Optional: Enable semihosting
$_TARGETNAME configure -event gdb-attach {
    echo "Debugger attached"
    reset init
}

Start OpenOCD:

# Terminal 1: Start OpenOCD
openocd -f openocd.cfg

# Output should show:
# Info : Listening on port 3333 for gdb connections

Connect GDB:

# Terminal 2: Start GDB
arm-none-eabi-gdb build/applications/blinky/blinky.elf

# In GDB:
(gdb) target extended-remote localhost:3333
(gdb) monitor reset halt
(gdb) load
(gdb) monitor reset init
(gdb) continue

GDB Commands ¶

Basic Commands:

# Load program
(gdb) load

# Set breakpoint
(gdb) break main
(gdb) break hal_gpio.c:123

# Run program
(gdb) continue
(gdb) run

# Step execution
(gdb) step          # Step into functions
(gdb) next          # Step over functions
(gdb) finish        # Step out of function

# Examine variables
(gdb) print variable_name
(gdb) print *pointer
(gdb) print array[5]

# Examine memory
(gdb) x/10x 0x20000000    # 10 hex words
(gdb) x/10i $pc           # 10 instructions at PC

# Backtrace
(gdb) backtrace
(gdb) bt full

# Watchpoints
(gdb) watch variable_name
(gdb) rwatch variable_name  # Read watchpoint
(gdb) awatch variable_name  # Access watchpoint

Advanced Commands:

# Conditional breakpoint
(gdb) break main if argc > 1

# Breakpoint commands
(gdb) break hal_gpio_write
(gdb) commands
> print port
> print pin
> print value
> continue
> end

# Display expressions
(gdb) display variable_name
(gdb) display/x register

# Examine registers
(gdb) info registers
(gdb) info all-registers

# Examine threads (RTOS)
(gdb) info threads
(gdb) thread 2

GDB Init Script ¶

Create .gdbinit in project root:

# Connect to OpenOCD
target extended-remote localhost:3333

# Load symbols
file build/applications/blinky/blinky.elf

# Reset and halt
monitor reset halt

# Load program
load

# Set breakpoint at main
break main

# Start execution
continue

# Enable pretty printing
set print pretty on
set print array on

Then simply run:

arm-none-eabi-gdb

J-Link Debugger ¶

J-Link GDB Server:

# Start J-Link GDB Server
JLinkGDBServer -device STM32F407VG -if SWD -speed 4000

# Connect GDB
arm-none-eabi-gdb build/app.elf
(gdb) target remote localhost:2331

J-Link RTT (Real-Time Transfer):

#include "SEGGER_RTT.h"

void debug_output(void)
{
    SEGGER_RTT_printf(0, "Debug message: %d\n", value);
}

IDE Integration ¶

VS Code ¶

Install Extensions:

C/C++ (Microsoft)
Cortex-Debug
CMake Tools

launch.json Configuration:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Debug STM32F4",
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "openocd",
            "cwd": "${workspaceRoot}",
            "executable": "${workspaceRoot}/build/applications/blinky/blinky.elf",
            "device": "STM32F407VG",
            "configFiles": [
                "interface/stlink.cfg",
                "target/stm32f4x.cfg"
            ],
            "svdFile": "${workspaceRoot}/vendors/st/STM32F407.svd",
            "runToMain": true,
            "preLaunchTask": "build"
        }
    ]
}

tasks.json for Build:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "type": "shell",
            "command": "cmake",
            "args": [
                "--build",
                "build",
                "--config",
                "Debug"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ]
}

Eclipse ¶

Setup:

Install Eclipse IDE for Embedded C/C++ Developers
Install GNU MCU Eclipse plugins
Configure ARM toolchain path
Import CMake project

Debug Configuration:

Run → Debug Configurations
GDB Hardware Debugging → New
Configure: * C/C++ Application: path to .elf * GDB Command: arm-none-eabi-gdb * Remote Target: localhost:3333 * Startup: load image, set breakpoint at main

CLion ¶

CMake Configuration:

CLion automatically detects CMakeLists.txt.

Embedded Development Plugin:

Install "Embedded Development Support" plugin.

Debug Configuration:

Run → Edit Configurations
Add → Embedded GDB Server
Configure target and GDB server settings

Common Debugging Scenarios ¶

Hard Fault Debugging ¶

Symptoms:

Program crashes
Enters HardFault_Handler
System becomes unresponsive

Debugging Steps:

Enable Fault Handlers:

void HardFault_Handler(void)
{
    /* Capture fault information */
    volatile uint32_t* cfsr = (uint32_t*)0xE000ED28;
    volatile uint32_t* hfsr = (uint32_t*)0xE000ED2C;
    volatile uint32_t* mmfar = (uint32_t*)0xE000ED34;
    volatile uint32_t* bfar = (uint32_t*)0xE000ED38;

    LOG_FATAL("HardFault!");
    LOG_FATAL("CFSR: 0x%08lX", *cfsr);
    LOG_FATAL("HFSR: 0x%08lX", *hfsr);
    LOG_FATAL("MMFAR: 0x%08lX", *mmfar);
    LOG_FATAL("BFAR: 0x%08lX", *bfar);

    /* Infinite loop for debugging */
    while (1) {
        __asm("NOP");
    }
}

Examine Stack:

(gdb) backtrace
(gdb) info registers
(gdb) x/32x $sp

Common Causes:

Null pointer dereference
Stack overflow
Invalid memory access
Unaligned access
Division by zero

Memory Corruption ¶

Symptoms:

Variables change unexpectedly
Random crashes
Data corruption

Debugging Techniques:

Watchpoints:

(gdb) watch my_variable
(gdb) continue

Memory Protection:

/* Add guard bytes */
#define GUARD_BYTE 0xDEADBEEF

typedef struct {
    uint32_t guard_start;
    uint8_t data[256];
    uint32_t guard_end;
} protected_buffer_t;

void check_guards(protected_buffer_t* buf)
{
    NX_ASSERT(buf->guard_start == GUARD_BYTE);
    NX_ASSERT(buf->guard_end == GUARD_BYTE);
}

Stack Canaries:

Enable stack protection:

add_compile_options(-fstack-protector-strong)

Task Debugging (RTOS)¶

FreeRTOS Thread Awareness:

GDB with FreeRTOS plugin:

# List tasks
(gdb) info threads

# Switch to task
(gdb) thread 3

# Task backtrace
(gdb) bt

Task State Inspection:

void debug_task_info(void)
{
    osal_task_handle_t current = osal_task_get_current();

    LOG_DEBUG("Current task: %s", osal_task_get_name(current));
    LOG_DEBUG("Priority: %d", osal_task_get_priority(current));
    LOG_DEBUG("Stack high water: %lu",
              osal_task_get_stack_high_water(current));
}

Deadlock Detection:

/* Timeout on mutex locks */
if (osal_mutex_lock(mutex, 5000) != OSAL_OK) {
    LOG_ERROR("Mutex lock timeout - possible deadlock");
    /* Dump task states */
    debug_all_tasks();
}

Peripheral Debugging ¶

GPIO:

void debug_gpio_state(char port, uint8_t pin)
{
    nx_gpio_t* gpio = nx_factory_gpio(port, pin);
    if (gpio) {
        uint8_t state = gpio->read(gpio);
        LOG_DEBUG("GPIO %c%d = %d", port, pin, state);
        nx_factory_gpio_release(gpio);
    }
}

UART:

void debug_uart_status(nx_uart_t* uart)
{
    nx_status_t status = uart->get_status(uart);
    LOG_DEBUG("UART status: 0x%08X", status);

    /* Check for errors */
    if (status & UART_ERROR_OVERRUN) {
        LOG_WARN("UART overrun error");
    }
    if (status & UART_ERROR_FRAMING) {
        LOG_WARN("UART framing error");
    }
}

SPI:

void debug_spi_transfer(nx_spi_t* spi,
                        const uint8_t* tx_data,
                        uint8_t* rx_data,
                        size_t len)
{
    LOG_DEBUG("SPI transfer: %zu bytes", len);

#ifdef DEBUG
    LOG_DEBUG("TX:");
    for (size_t i = 0; i < len; i++) {
        LOG_DEBUG("  [%zu] = 0x%02X", i, tx_data[i]);
    }
#endif

    nx_status_t status = spi->transfer(spi, tx_data, rx_data, len, 1000);

#ifdef DEBUG
    if (status == NX_OK) {
        LOG_DEBUG("RX:");
        for (size_t i = 0; i < len; i++) {
            LOG_DEBUG("  [%zu] = 0x%02X", i, rx_data[i]);
        }
    }
#endif
}

Performance Profiling ¶

Timing Measurements ¶

Simple Timing:

uint32_t start = osal_get_time_ms();

/* Code to measure */
perform_operation();

uint32_t elapsed = osal_get_time_ms() - start;
LOG_INFO("Operation took %lu ms", elapsed);

High-Resolution Timing:

/* Use hardware timer for microsecond precision */
uint32_t start = hal_timer_get_counter(TIMER_0);

/* Code to measure */
perform_operation();

uint32_t end = hal_timer_get_counter(TIMER_0);
uint32_t cycles = end - start;
uint32_t us = cycles / (SystemCoreClock / 1000000);

LOG_INFO("Operation took %lu us (%lu cycles)", us, cycles);

Function Profiling:

#ifdef PROFILE
#define PROFILE_START(name) \
    uint32_t __profile_##name##_start = osal_get_time_ms()

#define PROFILE_END(name) \
    do { \
        uint32_t __elapsed = osal_get_time_ms() - __profile_##name##_start; \
        LOG_INFO("PROFILE: %s took %lu ms", #name, __elapsed); \
    } while (0)
#else
#define PROFILE_START(name)
#define PROFILE_END(name)
#endif

void my_function(void)
{
    PROFILE_START(my_function);

    /* Function code */

    PROFILE_END(my_function);
}

CPU Usage Monitoring ¶

FreeRTOS Runtime Stats:

#if (configGENERATE_RUN_TIME_STATS == 1)
void print_task_stats(void)
{
    char stats_buffer[512];
    vTaskGetRunTimeStats(stats_buffer);
    LOG_INFO("Task Statistics:\n%s", stats_buffer);
}
#endif

Idle Task Hook:

void vApplicationIdleHook(void)
{
    static uint32_t idle_count = 0;
    idle_count++;

    /* Log CPU usage periodically */
    if (idle_count % 10000 == 0) {
        uint32_t cpu_usage = calculate_cpu_usage();
        LOG_DEBUG("CPU usage: %lu%%", cpu_usage);
    }
}

Memory Debugging ¶

Stack Usage ¶

Check Stack High Water Mark:

void check_stack_usage(void)
{
    osal_task_handle_t current = osal_task_get_current();
    uint32_t high_water = osal_task_get_stack_high_water(current);
    uint32_t stack_size = osal_task_get_stack_size(current);
    uint32_t used = stack_size - high_water;
    uint32_t percent = (used * 100) / stack_size;

    LOG_INFO("Stack usage: %lu/%lu bytes (%lu%%)",
             used, stack_size, percent);

    if (percent > 80) {
        LOG_WARN("Stack usage high!");
    }
}

Stack Overflow Detection:

/* FreeRTOS stack overflow hook */
void vApplicationStackOverflowHook(TaskHandle_t xTask, char* pcTaskName)
{
    LOG_FATAL("Stack overflow in task: %s", pcTaskName);
    /* Handle error */
    while (1);
}

Heap Usage ¶

Monitor Heap:

void check_heap_usage(void)
{
    size_t free_heap = osal_get_free_heap_size();
    size_t min_free = osal_get_minimum_ever_free_heap_size();

    LOG_INFO("Free heap: %zu bytes", free_heap);
    LOG_INFO("Minimum free heap: %zu bytes", min_free);

    if (free_heap < 1024) {
        LOG_WARN("Low memory!");
    }
}

Memory Leak Detection:

#ifdef DEBUG
static size_t alloc_count = 0;
static size_t free_count = 0;

void* debug_malloc(size_t size)
{
    void* ptr = malloc(size);
    if (ptr) {
        alloc_count++;
        LOG_DEBUG("malloc(%zu) = %p [count=%zu]",
                  size, ptr, alloc_count);
    }
    return ptr;
}

void debug_free(void* ptr)
{
    if (ptr) {
        free_count++;
        LOG_DEBUG("free(%p) [count=%zu]", ptr, free_count);
        free(ptr);
    }
}

void check_memory_leaks(void)
{
    if (alloc_count != free_count) {
        LOG_WARN("Memory leak detected: %zu allocs, %zu frees",
                 alloc_count, free_count);
    }
}
#endif

Platform-Specific Debugging ¶

STM32 Debugging ¶

SWO (Serial Wire Output):

/* Enable SWO output */
void swo_init(void)
{
    /* Configure SWO pin */
    /* Enable ITM */
    ITM->LAR = 0xC5ACCE55;
    ITM->TER = 0x1;
    ITM->TCR = 0x00010005;
}

/* Printf to SWO */
int _write(int file, char* ptr, int len)
{
    for (int i = 0; i < len; i++) {
        ITM_SendChar(ptr[i]);
    }
    return len;
}

ETM Trace:

Configure ETM for instruction trace in OpenOCD.

Native Platform Debugging ¶

Valgrind:

# Memory leak detection
valgrind --leak-check=full ./build/app

# Memory error detection
valgrind --tool=memcheck ./build/app

AddressSanitizer:

# Enable ASan
add_compile_options(-fsanitize=address)
add_link_options(-fsanitize=address)

GDB on Native:

gdb ./build/app
(gdb) run
(gdb) backtrace

Best Practices ¶

Use Appropriate Log Levels * TRACE for detailed flow * DEBUG for development * INFO for normal operation * WARN for recoverable issues * ERROR for failures * FATAL for critical errors
Add Context to Logs * Include relevant variable values * Log function parameters * Log return values * Include error codes
Use Assertions * Check preconditions * Validate parameters * Verify invariants * Catch programming errors early
Minimize Debug Impact * Use conditional compilation * Avoid blocking operations in debug code * Be mindful of timing changes * Use async logging when possible
Document Debug Features * Document debug commands * Explain debug output format * Provide troubleshooting guides * Include debug build instructions
Version Control Debug Code * Keep debug code in version control * Use feature flags for debug features * Don't commit temporary debug code * Review debug code in code reviews

Troubleshooting ¶

Common Issues ¶

GDB Connection Fails

Check OpenOCD is running
Verify correct port (3333)
Check firewall settings
Try different debug adapter

Breakpoints Don't Work

Verify debug symbols (-g flag)
Check optimization level
Ensure code is not in ROM
Try hardware breakpoints

Variables Optimized Out

Use -Og optimization
Mark variables as volatile
Use -fno-omit-frame-pointer
Disable specific optimizations

Slow Debugging

Reduce log verbosity
Use hardware breakpoints
Increase GDB timeout
Check USB connection quality

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