CODEWITHSUNDEEP
serial-portavratmegausart
Bob
Bob

Reputation: 39

Broken data read from AVR USART transmission

I have an atmega162 chip on stk500 dev board connected to ubuntu with serial cable. On atmega, I initialize usart and write some bytes. On Ubuntu side, something comes out of the pipe, but it's definitely not what was sent...

To be more precise: For each byte sent, I get a series of about 6 or 7 bytes, each of them with either 0x00 or 0xC0 values.

Relevant snippets of my code:

compile flags:

CFLAGS = -g
CFLAGS += -mmcu=atmega162
CFLAGS += -W -Wall -Wshadow
CFLAGS += -Os
CFLAGS += -mcall-prologues
CFLAGS += -finline-limit=10
CFLAGS += -mno-interrupts
CFLAGS += -ffunction-sections
CFLAGS += -DF_CPU=7372800ULL

usart functions:

void Serial0Init(int baud)
{
        unsigned int    ubrr;

        ubrr = ((F_CPU+8*baud)/(16*baud))-1;
        // Baud rate
        UBRR0H = (unsigned char)(ubrr>>8);
        UBRR0L = (unsigned char)ubrr;
        UCSR0A &= ~(1 << U2X0); // U2X off
        // Transmission settings
        UCSR0C = (1<<URSEL0)|(3<<UCSZ00);       // 8N1
        UCSR0B = (1<<RXEN0)|(1<<TXEN0);
}

unsigned char Serial0CheckTxReady()
{
        return (UCSR0A&_BV(UDRE0));     // nonzero if transmit register is ready to receive new data.
}

void Serial0Write(unsigned char data)
{
        while (Serial0CheckTxReady()==0)        // while NOT ready to transmit
                {}
        UDR0 = data;
}

main code:

Serial0Init(9600);
Serial0Write('!');

I receive data with simple python script:

import serial
import os

port = serial.Serial('/dev/ttyS0', 9600)

print 'Reading from serial...'
while True:
  c = port.read()
  print c, ord(c)

I double checked byte size settings and baud rate calculations, and everything seems okay... Any ideas what I'm doing wrong?

Upvotes: 2

Views: 1992

Answers (1)

Rev
Rev

Reputation: 6132

As far as I can tell (and was already suspected in the comments), the baud rate calculation is wrong.
Try

UBRR = ((fOSC / (16 * BAUD)) - 1

what results in 

UBRR = 47

for 9600 @ 7372800MHz.

Upvotes: 1

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