# Bootloader start address (ATMega 128, 1024)
BOOTLOADER_ADDRESS = 0x1F800

#---------------- Linker Options ----------------

LDFLAGS += -Wl,--section-start=.text=$(BOOTLOADER_ADDRESS)

//UART0 initialize
// desired baud rate: 500000
// actual: baud rate:500000 (0,0%)
// char size: 8 bit
// parity: Disabled
void USART0_Initialize(void) // initialization
{    
    UCSR0B = 0x00; //disable while setting baud rate
    UCSR0A = 0x00;
    UCSR0C = (_BV(UCSZ01) | _BV(UCSZ00));
    UBRR0L = 0x01; //set baud rate lo
    UBRR0H = 0x00; //set baud rate hi
    UCSR0B = (_BV(RXEN0) | _BV(TXEN0));        
}

BYTE USART0_GetChar(void)
{
    while(!(UCSR0A & _BV(RXC0)));
    return UDR0;
}

void USART0_PutChar(BYTE data)
{
    while(!( UCSR0A & _BV(UDRE0)));
    UDR0 = data;
}

void Initialize(void)
{
    ACSR |= _BV(ACD); // disable Analog Comparator
    MCUCSR |= _BV(JTD); // disable JTAG; need to set JTD twice within a 4 cycles; refer to ATMega128 daatasheet for detais
    MCUCSR |= _BV(JTD);        
    USART0_Initialize();
}

void boot_program_page(uint32_t page, uint8_t *buf)
{
    uint16_t i;

    eeprom_busy_wait();
    boot_page_erase(page);
    boot_spm_busy_wait();      // Wait until the memory is erased.

    for(i = 0; i < SPM_PAGESIZE; i += 2)
    {
        // Set up little-endian word.

        uint16_t w = *buf++;
        w += (*buf++) << 8;
    
        boot_page_fill(page + i, w);
    }

    boot_page_write(page);     // Store buffer in flash page.
    boot_spm_busy_wait();       // Wait until the memory is written.

    // Reenable RWW-section again. We need this if we want to jump back
    // to the application after bootloading.

    boot_rww_enable ();
}

int main(void)
{
    BYTE data, mode = 0;
    WORD idx = 0;
    uint8_t data_buf[SPM_PAGESIZE];
    Initialize();
    while(TRUE)
    {
        data = USART0_GetChar();
        switch(data)
        {
            case 'S':
                USART0_PutChar('D');
                USART0_PutChar('a');
                USART0_PutChar('t');
                USART0_PutChar('a');
                USART0_PutChar('>');
                USART0_PutChar(' ');
                idx = 0;
                mode = 1;
                break;
            case 'W':                
                USART0_PutChar(' ');
                USART0_PutChar('W');
                USART0_PutChar('a');
                USART0_PutChar('i');
                USART0_PutChar('t');
                USART0_PutChar('.');
                USART0_PutChar('.');
                USART0_PutChar('.');
                mode = 0;
                boot_program_page(0, data_buf);
                USART0_PutChar('O');
                USART0_PutChar('K');
                USART0_PutChar('!');
                USART0_PutChar(' ');
                break;
            default:
                if(mode)
                {
                    USART0_PutChar(data);
                    data_buf[idx++] = data;
                    if(idx >= SPM_PAGESIZE) idx = 0;
                }
                break;
        }
    }
    return 0;
}