/**
 * @file main.c
 * @brief CAIIC minimal bootloader: bootsetting arbitration, vector sanity
 *        check, vector remap and jump to the active application bank.
 *
 * No interrupts, no peripherals: flash is read through the memory map only.
 *
 * Policy: the application image CRC is verified during the OTA process
 * (app_ota.c) BEFORE bootsetting is switched - boot itself never validates
 * image contents, it only trusts the bootsetting sector integrity
 * (magic + own CRC32) to pick the active bank, then jumps straight to it.
 * If the chosen vector table looks dead the CPU stays here forever
 * (recover via SWD).
 */
#include <stddef.h>
#include "n32wb03x.h"

#include "dfu_layout.h"
#include "boot_crc32.h"

/**
 * @brief  Sanity check of an app vector table at @p base.
 * @return 1 if MSP points into SRAM and the reset vector into the bank.
 */
static int bank_vector_ok(uint32_t base)
{
    uint32_t msp   = *(volatile uint32_t*)base;
    uint32_t reset = *(volatile uint32_t*)(base + 4) & ~1u;

    return ((msp & 0xFFFF0000u) == 0x20000000u) &&
           (reset >= base) && (reset < base + CAIIC_APP_BANK_SIZE);
}

/**
 * @brief  Remap the vector table to the app and jump to it. Never returns.
 */
static void jump_to_app(uint32_t base)
{
    typedef void (*app_entry_t)(void);

    __disable_irq();
    PWR->VTOR_REG = CAIIC_VTOR_EN | base;   /* Cortex-M0 has no SCB->VTOR */
    __set_MSP(*(volatile uint32_t*)base);
    ((app_entry_t)(*(volatile uint32_t*)(base + 4)))();

    for (;;)
    {
    }
}

/**
 * @brief  Main program.
 */
int main(void)
{
    const caiic_bootsetting_t* bs = (const caiic_bootsetting_t*)CAIIC_BOOTSETTING_ADDR;
    uint32_t target = CAIIC_APP1_BASE;      /* default bank */

    /* Pick the active bank. Only the bootsetting sector integrity is
     * checked (magic + its own CRC32); the app image itself is NOT
     * verified here - it was already verified at OTA time before this
     * record was written. */
    if (bs->magic == CAIIC_BOOT_MAGIC &&
        bs->crc32 == caiic_crc32((const uint8_t*)bs, offsetof(caiic_bootsetting_t, crc32)) &&
        bs->active_bank == CAIIC_ACTIVE_BANK2)
    {
        target = CAIIC_APP2_BASE;
    }

    /* Last-resort sanity: never jump into a blank/garbage vector table */
    if (bank_vector_ok(target))
    {
        jump_to_app(target);
    }

    for (;;)
    {
    }
}