linuxperlserial-portat-commandmodem

Use perl to send AT commands to modem

I have a embedded Linux box with perl 5.10 and a GSM modem attached. I have written a simple perl script to read/write AT commands through the modems device file (/dev/ttyACM0).

If I write a simple 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 (I do not have Device::Serialport on my embedded Linux perl installation):

open(FH, "+<", "/dev/ttyACM0") or die "Failed to open com port $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?

Solution

  • Thanks for your answer. Although not the explicit answer to my question it certainly brought me on the right track.

    As noted by mti2935 this was indeed not a perl problem, but a mere tty configuration problem.

    Using the stty command with the following parameters set my serial port in the "expected" mode:

    It is also possible to use the combination setting "raw" to set all these parameters the correct way.