Missing either data or entire lines on serial port read - perl

Question

I am trying to read streaming serial data at 115200b and cant seem to pick it all up.
using the input method ($data = $Port -> input), I get the first 14 or 15 characters of every line. I need the whole line.
using the read method ($data= $Port -> read(4096)) and by adjusting the read_interval I can either get partials of every line using
$Port->read_interval(1);
or fully every third line using
$Port->read_interval(2);
I need all of every line.
here is the code
my $App_Main_Port = Win32::SerialPort->start ($Test_cfgfile);
$App_Main_Port->read_interval(1);
$App_Main_Port->read_char_time(1);
for ($i=0;;) {
# $data = $App_Main_Port -> input;
$data= $App_Main_Port -> read(4096);
print "$data\n";
}
by adjusting the read interval I get the results mentioned above. I started with the default values of 100 in the interval and char_time parameters, but only get every third line.
Tx for any insight!
Chris

Answer 1

Serial port reads often just return what's buffered in the serial port at that moment. A 16550 UART only buffers 16 bytes total, and that's what most PCs emulate.
From the Win32::SerialPort page, it appears you need to call ->read() in a list context, so you can find out how many bytes actually got read. If you really do want to block until you've received all 4K characters, try a loop like this:
# read in 4K bytes
my ($data, $temp, $count_in, $total_in);
$total_in = 0;
while ($total_in < 4096) {
( $count_in, $temp ) = $App_Main_Port->read( 4096 - $total_in );
$data .= $temp;
$total_in += $count_in;
}
That said, your real problem sounds like it could be a flow control issue. Even with such a loop, you might still get dropped characters if you don't have proper flow control. You might experiment with handshake("dtr") or handshake("rts").