AVR Freaks

Hello forum,

I bought two arduino pro mini boards based on ATmega328P.

I wrote a program in Atmel Studio and I used avrdude and an ISP programmer (usbasp) to flash the hex.

My intention was to connect that tiny board with an RFM95 (LoRa module).

I didn't want to make a PCB from scratch. I found those boards very cheap and I decided to use them to make some LoRa nodes.

The problem is that UART seems lose its synchronization when timer0 is enabled.

Same thing happens when I use timer1 instead of timer0.

when the function SystemTimerInit() is executed, UART stopped working for some reason and I read gibberish on my terminal.

when timer0 (or timer1) is disabled it works fine.

Fuses are: (E:FD, H:D9, L:E2)

Chip runs at 8MHz with internal RC.

Board is powered through the ISP programmer at 3.3V I also used it with other power supply but it didn't work

UART BaudRate is 38400. The error according to datasheet is about 0.2%

This is the code for timer0

void SystemTimerInit( void )
{
	cpuTimeSinceLastBoot = ( uint64_t )0;
	TCCR0B = ( 1 << CS01 ) | ( 1 << CS00 );
	TIMSK0 = ( 1 << TOIE0 ); //Enable Timer0 Overflow Interrupt
	TCNT0 = 131;
}

ISR( TIMER0_OVF_vect )
{
	cpuTimeSinceLastBoot++;
	TCNT0 = 131;
}

this is the code for UART

void UartInit(void)
{
	UCSR0B |= (1 << RXEN0) | (1 << TXEN0);   // Use 8-bit character sizes - URSEL bit set to select the UCRSC register
	UCSR0C |= (1 << UCSZ00) | (1 << UCSZ01);   // Load upper 8-bits of the baud rate value into the high byte of the UBRR register
	UBRR0H = (uint8_t)(BAUD_PRESCALE >> 8);   // Load lower 8-bits of the baud rate value into the low byte of the UBRR register
	UBRR0L = (uint8_t)BAUD_PRESCALE;
}

uint8_t UartSendByte(uint8_t data)
{
	/* Wait for empty transmit buffer */
	while (!(UCSR0A & (1<<UDRE0)));
	/* Put data into buffer, sends the data */
	UDR0 = (data & 0xFF);
	return 1;
}

void PrintLine(char *data_ptr)
{
	while(*data_ptr)
	{
		UartSendByte(*(data_ptr++));
	}
	return;
}

and this is the main function

int main(void)
{
	UartInit();
	sei();
	SystemTimerInit();

	for (;;) // Loop forever
	{
		PrintLine("Test firmware\r\n");
	}
}