The "Holy Bible" for embedded engineers
Mastering code coverage analysis to ensure comprehensive testing and quality assurance in embedded software development
Code coverage is a critical metric in embedded software development that measures how much of your source code is executed during testing. Unlike desktop applications, embedded systems require careful consideration of hardware interactions, real-time constraints, and resource limitations when implementing coverage analysis.
┌─────────────────────────────────────────────────────────────┐
│ Code Coverage Types │
├─────────────────────────────────────────────────────────────┤
│ Statement Coverage │ Line-by-line execution tracking │
│ Branch Coverage │ Decision point coverage │
│ Function Coverage │ Function call/entry tracking │
│ Condition Coverage │ Boolean expression evaluation │
│ MC/DC Coverage │ Modified Condition/Decision │
│ Path Coverage │ Complete execution path tracking │
└─────────────────────────────────────────────────────────────┘
Statement coverage tracks the execution of individual statements in your code. In embedded systems, this includes:
Branch coverage ensures that both true and false outcomes of conditional statements are tested:
// Example: Hardware status checking
if (hardware_ready()) {
// This path must be tested
start_operation();
} else {
// This path must also be tested
handle_hardware_error();
}
Function coverage tracks which functions are called during testing:
// Coverage tracking structure
typedef struct {
uint32_t function_id;
uint32_t call_count;
uint32_t branch_mask;
uint32_t branch_hits;
bool is_called;
} function_coverage_t;
#define MAX_FUNCTIONS 100
#define MAX_BRANCHES 32
function_coverage_t coverage_data[MAX_FUNCTIONS];
uint32_t function_count = 0;
// Register function for coverage tracking
uint32_t register_function_coverage(const char *name, uint32_t branch_count) {
if (function_count >= MAX_FUNCTIONS) {
return UINT32_MAX; // Error
}
coverage_data[function_count].function_id = function_count;
coverage_data[function_count].call_count = 0;
coverage_data[function_count].branch_mask = (1 << branch_count) - 1;
coverage_data[function_count].branch_hits = 0;
coverage_data[function_count].is_called = false;
return function_count++;
}
// Track function call
void track_function_call(uint32_t function_id) {
if (function_id < function_count) {
coverage_data[function_id].call_count++;
coverage_data[function_id].is_called = true;
}
}
// Track branch execution
void track_branch_execution(uint32_t function_id, uint32_t branch_id) {
if (function_id < function_count && branch_id < MAX_BRANCHES) {
coverage_data[function_id].branch_hits |= (1 << branch_id);
}
}
// Automatic instrumentation using macros
#define COVERAGE_TRACK_FUNCTION(func_id) \
track_function_call(func_id)
#define COVERAGE_TRACK_BRANCH(func_id, branch_id) \
track_branch_execution(func_id, branch_id)
// Example usage
void hardware_init(void) {
COVERAGE_TRACK_FUNCTION(FUNC_HARDWARE_INIT);
if (check_hardware_status()) {
COVERAGE_TRACK_BRANCH(FUNC_HARDWARE_INIT, 0);
configure_hardware();
} else {
COVERAGE_TRACK_BRANCH(FUNC_HARDWARE_INIT, 1);
handle_hardware_error();
}
}
// Collect coverage data without blocking
void collect_coverage_data(void) {
static uint32_t last_collection = 0;
uint32_t current_time = get_system_time();
// Collect every 100ms to avoid interference
if (current_time - last_collection >= 100) {
// Store coverage data in non-volatile memory
store_coverage_data();
last_collection = current_time;
}
}
// Store coverage data efficiently
void store_coverage_data(void) {
// Use compression to save memory
compressed_coverage_t compressed;
for (uint32_t i = 0; i < function_count; i++) {
compressed.function_calls[i] = coverage_data[i].call_count;
compressed.branch_hits[i] = coverage_data[i].branch_hits;
}
// Store in flash or external memory
flash_write(COVERAGE_DATA_ADDR, &compressed, sizeof(compressed));
}
// Coverage for hardware-specific code paths
typedef struct {
uint32_t register_access_count;
uint32_t interrupt_handling_count;
uint32_t dma_operation_count;
uint32_t power_state_transitions;
} hardware_coverage_t;
// Track hardware register access
void track_register_access(uint32_t register_addr) {
// Use hardware breakpoints or memory protection
if (is_coverage_enabled()) {
hardware_coverage.register_access_count++;
}
}
// Track interrupt handling
void track_interrupt_handling(uint32_t irq_number) {
if (is_coverage_enabled()) {
hardware_coverage.interrupt_handling_count++;
}
}
// Non-blocking coverage analysis
typedef struct {
uint32_t coverage_timer;
uint32_t analysis_interval;
bool analysis_in_progress;
} real_time_coverage_t;
// Periodic coverage analysis
void periodic_coverage_analysis(void) {
if (!real_time_coverage.analysis_in_progress) {
// Start analysis in background
start_background_analysis();
real_time_coverage.analysis_in_progress = true;
}
}
// Background analysis completion
void on_analysis_complete(void) {
real_time_coverage.analysis_in_progress = false;
// Update coverage statistics
update_coverage_statistics();
// Generate coverage report if needed
if (coverage_report_requested()) {
generate_coverage_report();
}
}
// Generate coverage report
void generate_coverage_report(void) {
printf("=== Code Coverage Report ===\n");
uint32_t total_functions = 0;
uint32_t covered_functions = 0;
uint32_t total_branches = 0;
uint32_t covered_branches = 0;
for (uint32_t i = 0; i < function_count; i++) {
total_functions++;
if (coverage_data[i].is_called) {
covered_functions++;
}
// Count branches
uint32_t branch_count = __builtin_popcount(coverage_data[i].branch_mask);
total_branches += branch_count;
uint32_t hit_count = __builtin_popcount(coverage_data[i].branch_hits);
covered_branches += hit_count;
}
float function_coverage = (float)covered_functions / total_functions * 100.0f;
float branch_coverage = (float)covered_branches / total_branches * 100.0f;
printf("Function Coverage: %.1f%% (%u/%u)\n",
function_coverage, covered_functions, total_functions);
printf("Branch Coverage: %.1f%% (%u/%u)\n",
branch_coverage, covered_branches, total_branches);
}
Q: What is the difference between statement coverage and branch coverage? A: Statement coverage tracks execution of individual statements, while branch coverage ensures both true and false outcomes of conditional statements are tested. Branch coverage is more comprehensive and catches logic errors that statement coverage might miss.
Q: How do you handle coverage analysis in real-time embedded systems? A: Use non-blocking coverage collection, minimize instrumentation overhead, perform analysis in background tasks, and use efficient data structures to store coverage information without affecting timing constraints.
Q: How would you implement coverage tracking for interrupt service routines? A: Use hardware breakpoints, track ISR entry/exit points, maintain separate coverage data for ISRs, and ensure coverage tracking doesn’t interfere with interrupt timing requirements.
Q: What are the challenges of achieving high coverage in embedded systems? A: Hardware dependencies, real-time constraints, limited resources, error handling paths, power management code, and hardware-specific optimizations that may not execute during testing.
Q: How would you design a coverage system that works across multiple MCU cores? A: Use shared memory regions, implement atomic operations for coverage updates, synchronize coverage collection across cores, and use inter-core communication to aggregate coverage data.
Q: How do you ensure coverage analysis doesn’t affect system reliability? A: Implement coverage tracking as a separate, isolated module, use hardware features when available, implement fail-safe mechanisms, and thoroughly test the coverage system itself.
Next Steps: Explore Static Analysis for code quality assessment or Dynamic Analysis for runtime behavior analysis.