Perl for cummunicating with modem over serial

[Klaus Holst Jacobsen]

Hello
I have written a simple perl script to read/write AT commands through the modems device file (/dev/ttyACM0) on my OCG-E H5.

If i write a simle command like “ATZ\r” to the modem and wait for a response I receive very odd data like “\n\n\nATZ\n\n0\n\nOK\n\n\n\n\nATZ\n\n\n\n…” and the data keeps coming in. It almost seems like the response is garbled up with other data.

I would expect something like “ATZ\nOK\n” (if echo is enabled).

If i send the “ATZ” command manually with e.g. minicom everything works as expected.

This leads me to think it might be some kind of perl buffering issue, but that’s only guessing.

I open the device in perl like this:

open(FH, "+>", "/dev/ttyACM0") or die "Failed to open $comport";

And read the response one byte at a time with:

while(1) {
    my $response;
    read(FH, $response, 1);
    printf("hex response '0x%02X'\n", ord $response);
}

Am I missing some initialization or something else to get this right?

Regards
Klaus

[Klaus Holst Jacobsen]

Found the answer.

It was not with perl.
It was simply my low level tty settings that were way off.

It seems that tty’s support a range of \r and \n translation settings.
Set the tty in “raw” mode to receive exactly what your tty device sent fixed the behaviour.

Simply issue: “stty -F /dev/my_tty raw”

//Klaus

[Author]

Posts