void js_LoadConfig(void)
{
    U8 *p = (U8 *)(CONFIG_START_FLASH_ADDRESS);
    U8 last_seq = *p;
    U8 *pLastConfig = p;
    U8 buf[sizeof(jsContext.Cfg)];
    PJS_CONFIG pCfg = (PJS_CONFIG)buf;
    int i;

    for (i = 0; i < CONFIG_MIRROR_PAGE_COUNT; i++)
    {
        p += FLASH_PAGE_SIZE_BYTES;
        if (((U8)(last_seq + 1)) == *p)
        {
            last_seq = *p;
            pLastConfig = p;
        }
        else
        {
            p = pLastConfig;
            break;
        }
    }
    // at this point p - points to the address with the most fresh config record
    memcpy( buf, p, sizeof(buf));
    jsContext.LastLocation = (U32)p;
    jsContext.Cfg.Sequence = *p;

    // check CRC of the record
    if ( CRC16( buf, sizeof(buf) != 0 )
    {
        printf("CRC error exp=%2x, cur=%2x, flash_addr=%x, seq=%d\n", hCRC, pCfg->CRC, (U32)p, *p);
        printf("The configuration has NOT been applied!\n" );
        printf("or there is no previously saved configuration.\n");
        // store defaults
        js_StoreConfig();
    }
    else
    {
        // CRC is ok, applying new settings
        memcpy( &jsContext.Cfg, pCfg, sizeof(jsContext.Cfg));
        printf("Configuration applied, seq_%x\n", *p);
    }
}


void js_StoreConfig(void)
{
    jsContext.Cfg.Sequence += 1;
    jsContext.LastLocation += FLASH_PAGE_SIZE_BYTES;
    if (jsContext.LastLocation > CONFIG_LAST_FLASH_CELL_ADDRESS)
        jsContext.LastLocation = CONFIG_START_FLASH_ADDRESS;

    jsContext.Cfg.CRC = CRC16( (U8 *)&jsContext.Cfg, sizeof(jsContext.Cfg) - 2);
    iap_PageWrite( jsContext.LastLocation, (U32 *)&jsContext.Cfg, sizeof(jsContext.Cfg) );

    printf("configuration stored, L(%x), Sq(%x), (%d)bytes\n", jsContext.LastLocation, jsContext.Cfg.Sequence, sizeof(jsContext.Cfg));
}

sn[i+1] - sn[ i ] != 1

#include <stdio.h>

static char str[100];

#define EEPROM_ADDRESS_TO_DESTROY 4094U

uint32_t cycles_;
uint16_t cycles_1000_;

void show_cycles(uint8_t is_failed)
{
if(is_failed)
{
sprintf(str, "\r\nFAILED ON: %ld", cycles_);
}
else
{
sprintf(str, "\r\nCURRENT: %ld", cycles_);
}

for(uint8_t i = 0; i < 100; i++)
{
if(str[i]) USB_TransmitByte(str[i]);
else break;
}
}

void eeprom_write_no_check(uint16_t address, uint8_t data)
{
while(EECR & _BV(EEWE));

EEAR = address;

EEDR = data;

ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
{
EECR |= _BV(EEMWE);
EECR |= _BV(EEWE);
}
}

uint8_t eeprom_read_no_check(uint16_t address)
{
while(EECR & _BV(EEWE));

EEAR = address;

EECR |= _BV(EERE);

return EEDR;
}


__attribute__((OS_main)) int main(void)
{
USB_Initialize();

sei();

for(;;)
{
eeprom_write_no_check(EEPROM_ADDRESS_TO_DESTROY, 0xFF);

++cycles_;
++cycles_1000_;

if(eeprom_read_no_check(EEPROM_ADDRESS_TO_DESTROY) != 0xFF)
{
show_cycles(TRUE);

for(;;);
}

if(cycles_1000_ == 1000)
{
cycles_1000_ = 0;

show_cycles(FALSE);

for(uint8_t data = 1; data; data <<= 1)
{
eeprom_write_no_check(EEPROM_ADDRESS_TO_DESTROY, data);

++cycles_;
++cycles_1000_;

if(eeprom_read_no_check(EEPROM_ADDRESS_TO_DESTROY) != data)
{
show_cycles(TRUE);

for(;;);
}
}
}

if(USB_IsDataReceived())
{
if(USB_ReceiveByte() == '?')
{
show_cycles(FALSE);
}
}
}

return 0;
}