/******************************************************************************/
/* avr-gcc v 4.1.2 */
#include <avr/io.h>

#define BIT(b)    (1 << b)

void spi_transmit (unsigned char c)
   {
   asm ("wdr");
   SPDR = c;
   while (!(SPSR & BIT(SPIF)));
   }  
  
void spi_str_transmit (const unsigned char * str, unsigned char size, unsigned char no)
   {
   static const unsigned char cs_bit [] = {BIT(PB4), BIT(PB6)};
   PORTB &= ~cs_bit [no];
    
   for (;size--;)
      spi_transmit (*str++);
    
   PORTB |= cs_bit [no];    
   }  
/******************************************************************************/
void twi_transmit (unsigned char data, unsigned char flags, const unsigned char stat)
   {
   asm ("wdr");
   TWDR = data;
   TWCR = flags;    
   while (!(TWCR & BIT (TWINT)));
   }

void send_twi_addr (const char a)
   {
   twi_transmit (a, BIT(TWINT) | BIT(TWEN), 0x18);
   }  

void send_twi_byte (const char b)
   {
   twi_transmit (b, BIT(TWINT) | BIT(TWEN), 0x28);
   }      
  
unsigned char read_twi_byte (void)
   {
   twi_transmit (0xFF, BIT(TWEA) | BIT(TWINT) | BIT(TWEN), 0x50);
   return TWDR;
   }    
  
void twi_start (void)
   {
   twi_transmit (0xFF, BIT(TWSTA) | BIT(TWINT) | BIT(TWEN), TWI_START);
   }    
  
void twi_stop (void)
   {  
   TWCR = BIT (TWSTO) | BIT (TWINT) | BIT (TWEN);
   TWCR = BIT (TWSTO) | BIT (TWINT);
   }

/******************************************************************************/

void init (void)
   {
   DDRF |= BIT(PF4) | BIT(PF5) | BIT(PF6) | BIT(PF7);   /* all leds */
   PORTF |= BIT(PF4) | BIT(PF5) | BIT(PF6) | BIT(PF7);  /* on */
  
   asm ("wdr");

   WDTCR = BIT(WDCE) | BIT(WDE);
   WDTCR = BIT(WDP2) | BIT(WDP1) | BIT(WDP0);           /* watchdog timeout ~ 2 sec  */
   WDTCR = BIT(WDE);  

   DDRE = BIT (0x03);                                   /* w/r rs485 driver ctrl. output enable */

   DDRA |= BIT(PA3);                                    /* debug led */
   PORTA |= BIT(PA3);                                   /* off */
   PORTD |= BIT(PD3);                                   /* internal pullup resistor */

   PORTB = BIT(PB7) | BIT(PB6)  | BIT(PB5) | BIT(PB0) | BIT(PB4);  
   DDRB = BIT(PB7) | BIT(PB6) | BIT(PB5) | BIT(PB4) | BIT(PB2) | BIT(PB1) | BIT(PB0);  
  
   while (!(PIND & BIT(PD3)));                          /* wait pwr signal */
    
   SPCR = BIT(SPE) | BIT(MSTR) | (SPR0);                /* init SPI (250 kHz) */

/* Two wire interface initialization */
   TWSR = 0; /* <- setting prescaler */
   TWBR = 0;  /* F_CPU / 16;  Bit rate = 250 kHz */

   EIMSK = BIT(INT7) | BIT(INT6) | BIT(INT3);           /* Extrnal intr. 7, 6, 3  */
   EICRB = BIT(ISC71) | BIT(ISC61);                     /* Falling edge sens.  */
  
   EICRA = BIT(ISC31);                                  /* Falling edge sens. */

   PORTE = ~BIT(0x03);                                  /* w/r rs485 driver read enable */

   UCSR0B = BIT(RXCIE0) | BIT(TXCIE0) | BIT(RXEN0) | BIT(TXEN0); /* enable intr/ on recv/send  byte  usart0 */
   UCSR0C = BIT(UCSZ01) | BIT(UCSZ00) | BIT(UPM01) | BIT(UPM00); /* async, even parity, 2 stop bit 8 bit usart0 */
   init_r (0);       /* spi_str_transmit */
   init_r (1);       /* spi_str_transmit */
  
   reset_tm ();      /* r/w twi  */
   init_s ();        /* r/w twi  */
   init_m ();        /* eeprom_read ->  UBRR0H, UBRR0L; */
   clear_list ();    /* r/w twi  */
   asm ("sei");
   PORTF &= ~(BIT(PF4) | BIT(PF5) | BIT(PF6) | BIT(PF7)); /* leds off */
   }
  
void loop (void)
   {
   for (;;)
      { /* ... */ }
   }
  
int main (void)
   {
   init ();
   loop ();
   return 0;
   }

SIG_UART0_RECV:
push r16 ; 2
in r16, IO_PORT(SREG) ; 1
push r17 ; 2

lds r17, LED_PORT ; 2 /* atmega128 */
ori r17, RECV_LED ; 1
sts LED_PORT, r17 ; 2 /* atmega128 */

push r30 ; 2
push r31 ; 2

in r31, IO_PORT(UDR0) ; 1 /* atmega128 */

in r17, IO_PORT(UCSR0A) ; 1 /* atmega128 */
andi r17, parity_error ; 1
lds r30, modbus_line_state ; 2
or r30, r17 ; 1
sts modbus_line_state, r30 ; 2

lds r16, modbus_line_timeout; 2
out IO_PORT(TCNT0), r16 ; 1 /* atmega128 */

in r17, IO_PORT(TIMSK) ; 1 /* atmega128 */
ori r17, BIT(TOIE0) ; 1
out IO_PORT(TIMSK), r17 ; 1 /* atmega128 */

in r17, IO_PORT(TIFR) ; 1
ori r17, BIT(TOV0) ; 1
out IO_PORT(TIFR), r17 ; 1

mov r17, r31 ; 1

lds r30, rxtx_buffer_ptr ; 2
lds r31, rxtx_buffer_ptr + 1; 2

st Z+, r17 ; 2
cpi r30, lo8(rxtx_buffer + RECV_MODBUS_BUFFER_SIZE) /* buffer size <= 256 bytes */
breq HERE + 8 ; 1 / 2

sts rxtx_buffer_ptr, r30 ; 2
sts rxtx_buffer_ptr + 1, r31; 2

pop r31 ; 2
pop r30 ; 2
pop r17 ; 2
out IO_PORT(SREG), r16 ; 1
pop r16 ; 2
reti