I wrote a Perl script to control a BT 8x2 switcher via a serial port. I
did this so I can read the status of the switcher and have rdairplay
display it after a command is executed. The actual script is listed below.
When I tested the script, I found that it couldn't open the serial port
when I ran it from rdairplay, but worked perfectly from the command line.
I had it display the real and effective UID and GID to see what user
Rivendell was running the script as; to my astonishment, they were all
1000, which is the same user and group I am logged in as.
Yet doing a chmod o+rw /dev/ttyS0 made the problem go away, indicating
that it is indeed a permissions problem.
I hve no problem doin a chmod o+rw /dev/ttyS0 before starting Rivendell,
but I'd love to know how it's possible that a Perl script can show the
same UID and GID in Rivendell as on the command line (and this user is in
the dialout group), yet be unable to access a serial port when running
from Rivendell until the serial port is chmodded.
There are things about Rivendell and permissons I clearly don't
understand. Doesn't Rivendell always run as the user designated in
/etc/rd.conf (AudioOwner and AudioGroup)? This is RD 2.17.0, by the way.
Rob
=========================================================================
#!/usr/bin/perl
use Device::SerialPort qw( :PARAM :STAT 0.07);
sub getstat {
my $timeout = 1;
my $chars = 0;
my $buffer = '';
my $saw = '';
$p->read_char_time(0); # don't wait for each character
$p->read_const_time(100); # .1 second per unfulfilled read
while ($timeout > 0) {
($count,$saw) = $p->read(255);
if ($count > 0) {
$chars += $count;
$buffer .= $saw;
} else { $timeout-- }
}
return $buffer;
}
sub is_valid {
my $a = shift;
my $b = shift;
my $c = '';
my $i = 0;
my $k = $#$b;
for ($i = 0; $i <= $k; $i++) {
$c = shift @$b;
if ($a eq $c) { return 1 }
}
return 0;
}
sub parse {
my $a = shift;
my $o1 = '';
my $o2 = '';
my @a = ($a =~
/(\w\w)(\d{3})(\d{3})(\d{3})(\d{3})(\d{3})(\d{3})(\d{3})(\d{3})/);
my @b = ($a[$in] =~ /(\d)(\d)(\d)/);
my $o = '';
if ($b[1] eq '1') { $o .= $DST[1] . ',' }
if ($b[2] eq '1') { $o .= $DST[2] . ',' }
if ($o gt '') {
chop $o;
$o = $SRC[$in] . " -> " . $o;
} else { $o = $SRC[$in] . " -> MUTE" }
return $o;
}
sub rmllabel {
my $a = shift;
my @c = ('rmlsend',"--to-host=$HOST","LB $a" . '!');
system(@c);
}
# MAIN PROGRAM
$HOST = 'pelamis';
$PORT = '/dev/ttyS0';
@SRC = ('0','Air Studio','Source 2','Main Production','Source 4','Green Room',
'Source 6','Rivendell','Source 8');
@DST = ('0','All Xmtrs','Dest 2');
@SRX = ('1','2','3','4','5','6','7','8');
@DSX = ('0','1','2');
$in = $ARGV[0];
$out = $ARGV[1];
if ((&is_valid($in,'SRX')) && (&is_valid($out,'DSX'))) {
if ($p = Device::SerialPort->new($PORT)) {
$p->baudrate(2400);
$p->parity('none');
$p->databits(8);
$p->stopbits(1);
$p->handshake('none');
$p->write_settings;
$p->write('*' . $in . $out .'1' . "\r\n");
$a = &parse(&getstat);
&rmllabel($a);
$p->close;
undef $p;
} else { &rmllabel("Serial port error") }
} else { &rmllabel("Invalid parameters") }
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