init.c

// Based on libopencm3 project.
#include <stdint.h>

extern unsigned _data_loadaddr, _data, _edata, _ebss, _stack;

typedef void (*vector_table_entry_t)(void);

typedef struct {
    unsigned int *initial_sp_value; /**< Initial stack pointer value. */
    vector_table_entry_t reset;
    vector_table_entry_t nmi;
    vector_table_entry_t hard_fault;
    vector_table_entry_t memory_manage_fault; /* not in CM0 */
    vector_table_entry_t bus_fault;           /* not in CM0 */
    vector_table_entry_t usage_fault;         /* not in CM0 */
    vector_table_entry_t reserved_x001c[4];
    vector_table_entry_t sv_call;
    vector_table_entry_t debug_monitor;       /* not in CM0 */
    vector_table_entry_t reserved_x0034;
    vector_table_entry_t pend_sv;
    vector_table_entry_t systick;
} vector_table_t;

// A handler that does nothing, we use no interrupts
void null_handler(void) {
	while (1);
}

/* Less common symbols exported by the linker script(s): */
typedef void (*funcp_t) (void);

void main(void);

void __attribute__ ((naked)) reset_handler(void) {
	volatile unsigned *src, *dest;

	for (src = &_data_loadaddr, dest = &_data;
		dest < &_edata;
		src++, dest++) {
		*dest = *src;
	}

	while (dest < &_ebss)
		*dest++ = 0;

	/* Ensure 8-byte alignment of stack pointer on interrupts */
	/* Enabled by default on most Cortex-M parts, but not M3 r1 */
	volatile uint32_t *_scb_ccr = (uint32_t*)0xE000ED14U;
	*_scb_ccr |= (1 << 9);

	/* Call the application's entry point. */
	main();
}

// Vector table (bare minimal one)
__attribute__ ((section(".vectors")))
vector_table_t vector_table = {
	.initial_sp_value = &_stack,
	.reset = reset_handler,
	.nmi = null_handler,
	.hard_fault = null_handler,
	.memory_manage_fault = null_handler,
	.bus_fault = null_handler,
	.usage_fault = null_handler,
	.debug_monitor = null_handler,
	.sv_call = null_handler,
	.pend_sv = null_handler,
	.systick = null_handler,
};