Linux Remove UART extra characters

Question

Working on linux, sending data to the serial port at 115200 bauds using:

echo -e "\x1B\x11\x00\x00" > /dev/ttyAMA0

The receiver side is reading the following data:

\xF8\x1B\x11\x00\x00\x0D\x0A

I dont want \\xF8 as starting byte and \\x0D\\x0A as tails (carriage return and new line bytes). How could I remove them? So far all I found is

stty raw -F /dev/ttyAMA0

This deactivates the \\x0D , but i want to get rid of \\xF8 and \\x0A and no other options have worked for me.

Answer 1

You can eliminate the newline with echo -en . Or use printf instead.

Are you sending from a raspberry pi? It seems to be a known issue that 0xF8 is sent each time the connection is opened (eg by calling echo ). I don't know if there's a fix but you can keep the connection open to prevent further 0xF8 's by using a serial terminal program.

There's an example in the third post here that shows how to keep the connection using a redirection in bash: exec 9> /dev/ttyAMA0
http://www.raspberrypi.org/forums/viewtopic.php?t=34528&p=293067

The underlying problem:
Some say it's a driver issue (see this answer ) but as far as i understand, the following indicates that it's hardware related:

http://elinux.org/RPi_Serial_Connection#Glitch_when_opening_serial_port
When the serial port is opened the voltage on TXD pulses negative for approximately 32 us (regardless of the baud rate). This pulse may be interpreted as a transmission by a device connected to the TXD pin, which could have unintended effects.

This also means that the garbage you receive is dependant on the baud rate. I wouldn't rely on a fix and look for a workaround instead.

If you have control over the receiver, you could make it wait for a self-defined sequence of bytes and only start operating after this sequence has been received.

The link to elinux.org above could give you some other ideas.

Answer 2

EDITED*

what about using stty to change how your device terminal is interpreting carriage return and newline character?

link

http://www.computerhope.com/unix/ustty.htm

********************OLD ANSWER*******************

What about using sed to remove "\\xF8" and "\\x0D\\x0A"?

 sed -e 's/\\x0D\\x0A$//g' -e 's/^\\xF8//g' my_file > new_file

pratical example?

echo '\xF8\x1B\x11\x00\x00\x0D\x0A' |sed -e 's/\\x0D\\x0A$//g' -e 's/^\\xF8//g'

output

\x1B\x11\x00\x00