[AVR] Receiving Data with using a State Machine

[vitruvius]

Hello,

I am sending some data from one Atmega644P to another Atmega644P consecutively. The first three bytes are SYN(0x16), DLE(0x10), and STX(0x02). On the receiving part, I made a state machine to control if I receive those bytes correctly.

When it is in DLE_1_s state, it goes directly to the "else" statement, even though the data is 0x10. Why is this happening?

I am using Peter Fleury's uart library.

This is the flow chart diagram I am trying to implement:

This is the code:

int main(void)
{
	DDRD = 0b11111010;	//	PORTD input/output.
	DDRC = 0xFF;
	
	uart_init( UART_BAUD_SELECT(UART_BAUD_RATE,F_CPU) );
	
	sei();

	unsigned int rec_char;
	char buffer[7];
	
    while(1)
    {
        rec_char=uart_getc();
        
        switch(state)
        {
	        case SYN_s:
				{					
					if ((unsigned char) rec_char == 0x16) // SYN
					{
						state=DLE_1_s;
					}
					else
					{
						state=SYN_s;
					}
				}
			break;
				
			case DLE_1_s:
				{
					if ((unsigned char) rec_char == 0x10) // DLE
					{
						state=STX_s;
					}
					else if ((unsigned char) rec_char == 0x16) // SYN
					{
						state=DLE_1_s;
					}
					else
					{
						state=SYN_s;
					}
				}
			break;
			
			case STX_s:
				{
					if ((unsigned char) rec_char == 0x02) // STX
					{
						state=TARGET_NO_1_s;
					}
					else if ((unsigned char) rec_char == 0x16) // SYN
					{
						state=DLE_1_s;
					}
					else
					{
						state=SYN_s;
					}
				}
			break;

Thank you.

 

[Gorgon]

If you take a look at the assembly code generated, you may see what is happening.

You could also add a second level of case statment under each state.

 

[vitruvius]

Unfortunately I do not know how to read the assembly code.

What is the second level of case statement for?