Thats what I would try:

open(COM,"< /dev/ttyS0")
[download]

Then try the rewind. I have a few examples of reading serial ports that seem to work on linux, if you want I could mail them off to you. You might want to look at Device::SerialPort;

Here is a nice explanation-script I found once on the net.

#!/usr/bin/perl                                                       
+                                                                     
+           
                                                                      
+                                                                     
+           
#the ubiquitous RS-232 Serial Port.  built an interface               
+                                                                     
+           
#for my Aware Electronics Geiger Counter (RM-70) that                 
+                                                                     
+           
#used a Basic Stamp IISX chip set. Every 20 seconds it                
+                                                                     
+           
#would spit out an ASCII string of radiation and                      
+                                                                     
+           
#temperature data. I had hunted around for examples                   
+                                                                     
+           
#using the Device::SerialPort module and found many.                  
+                                                                     
+           
#Most were copies of code used to read PBX data. But                  
+                                                                     
+           
#it wouldn't work. Ouch. Finally, after much research                 
+                                                                     
+           
#I realized that - by golly - you had to terminate                    
+                                                                     
+           
#the IO with a new line and not a carriage return.                    
+                                                                     
+           
#Oddly doing a cat </dev/ttyS0 worked, which faked me                 
+                                                                     
+           
#out. So I added the line in the tty setup below that                 
+                                                                     
+           
#converts CR to NL and zap-ity-do-dah it started terminating          
+                                                                     
+           
#and sending each read. Long live RS-232. Please send                 
+                                                                     
+           
#along any suggestions and improvements. This also probably           
+                                                                     
+           
#explains why I had failed to get good reads from a                   
+                                                                     
+           
#cheap-o RS-232 capable DVM a few years ago.                          
+                                                                     
+           
                                                                      
+                                                                     
+           
#This was done in Perl 5.8.0 under RH Linux 9.0.                      
+                                                                     
+           
                                                                      
+                                                                     
+           
#file geiger.pl                                                       
+                                                                     
+           
#                                                                     
+                                                                     
+           
# Author: David Drake                                                 
+                                                                     
+           
# Date:   July 18, 2003                                               
+                                                                     
+           
# Requirements: Device::SerialPort 0.22 (from cpan  July 2003)        
+                                                                     
+           
#                                                                     
+                                                                     
+           
# Version: 1.0                                                        
+                                                                     
+           
#This script is used to read a serial port to obtain data from a      
+                                                                     
+           
#combined Geiger counter and temperature sensor.                      
+                                                                     
+           
#The Geiger Counter is an Aware Electronics RM-70 unit. Each count    
+                                                                     
+           
#maps to one microR per hour. The RM-70 pulse output is sent to a     
+                                                                     
+           
#Basic Stamp-IISX microcontroller. The BS2SX accumulates counts for 20
+                                                                     
+           
#seconds and then sends a serial data stream out of its serial port.  
+                                                                     
+           
#The data stream goes into the input serial port on the Linux system. 
+                                                                     
+           
#This program then tabulates the data to a log file.                  
+                                                                     
+           
                                                                      
+                                                                     
+           
use Device::SerialPort;                                               
+                                                                     
+           
use Time::gmtime;                                                     
+                                                                     
+           
                                                                      
+                                                                     
+           
$LOGDIR  = "/home/zentara/perlplay/serial-comm";    # path to data fil
+e                                                                    
+           
$LOGFILE = "geiger.log";                      # file name to output to
+                                                                     
+           
$PORT    = "/dev/ttyS1";                      # port to watch         
+                                                                     
+           
                                                                      
+                                                                     
+           
#                                                                     
+                                                                     
+           
#                                                                     
+                                                                     
+           
# Serial Settings                                                     
+                                                                     
+           
#                                                                     
+                                                                     
+           
                                                                      
+                                                                     
+           
#make the serial port object                                          
+                                                                     
+           
#note the need to convert carriage returns to new lines to terminate e
+ach                                                                  
+           
#read.                                                                
+                                                                     
+           
                                                                      
+                                                                     
+           
$ob = Device::SerialPort->new($PORT) || die "Can't Open $PORT: $!";   
+                                                                     
+           
                                                                      
+                                                                     
+           
$ob->baudrate(9600)    || die "failed setting baudrate";              
+                                                                     
+           
$ob->parity("none")    || die "failed setting parity";                
+                                                                     
+           
$ob->databits(8)       || die "failed setting databits";              
+                                                                     
+           
$ob->stty_icrnl(1)     || die "failed setting convert cr to new line";
+                                                                     
+           
$ob->handshake("none") || die "failed setting handshake";             
+                                                                     
+           
                                                                      
+                                                                     
+           
$ob->write_settings || die "no settings";                             
+                                                                     
+           
                                                                      
+                                                                     
+           
#                                                                     
+                                                                     
+           
# open the logfile, and Port                                          
+                                                                     
+           
#                                           
open( LOG, ">>${LOGDIR}/${LOGFILE}" )                                 
+                                                                     
+           
  || die "can't open smdr file $LOGDIR/$LOGFILE for append: $SUB $!\n"
+;                                                                    
+           
                                                                      
+                                                                     
+           
select(LOG), $| = 1;    # set nonbuffered mode, gets the chars out NOW
+                                                                     
+           
                                                                      
+                                                                     
+           
open( DEV, "<$PORT" ) || die "Cannot open $PORT: $_";                 
+                                                                     
+           
                                                                      
+                                                                     
+           
#                                                                     
+                                                                     
+           
# Loop forver, logging data to the log file                           
+                                                                     
+           
#                                                                     
+                                                                     
+           
                                                                      
+                                                                     
+           
while ( $_ = <DEV> ) {    # print input device to file                
+                                                                     
+           
    $gmc = gmctime();                                                 
+                                                                     
+           
    print LOG $gmc, " ", $_;                                          
+                                                                     
+           
}                                                                     
+                                                                     
+           
                                                                      
+                                                                     
+           
undef $ob;                                                            
+                                                                     
+           
                                                                      
+                                                                     
+           
#we are done dude
[download]

---

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