AB 144 I N F O R M A T I O N R E L E A S E
Sco Unix and Charisma
Charisma normally uses a direct print feature. This means it bypasses lp and writes print jobs directly to the device file.
After a system boot SCO Unix does not enable Xon/Xoff for serial ports.
Unless this is resolved then data loss will occur when these "direct print jobs" are generated.
Flow control is enabled during bootup with the following file.
/etc/rc.d/8/userdef
An entry is added to the end of this file for each serial printer defined on the system as follows.
(stty 9600 cs8 ixon ixoff onlcr;cat>/dev/null)/p>
The ?? in the device name is replaced with the appropriate device name of the printer i.e. ttya16.
This will work all the time the printer device is accessed directly through Charisma. However if the printer is accessed via the Unix lp spooler the process keeping the flow control active will die. This is also the case when a Charisma user prints to DISK and then uses the Charisma SPOOL program to print the report (this makes use of the lp spooler). This means that once the lp process has finished printing, the port will revert to the Unix default of not having any flow control running on the port.
When Charisma then directly prints to the port again data can be lost due to buffer over-runs in the printer.
This can be overcome however by modifying the lp interface script for each serial printer port as follows.
For Sco Unix version prior to Open Server the lp interface scripts are held in the directory.
/usr/spool/lp/admins/lp/interfaces
For Sco Open Server the lp interface scripts are held in the directory.
/var/spool/lp/admins/lp/interfaces
This directory contains files that are named after the printer queue that they relate to i.e. LP01, LP02 etc.
A sample interface script is shown on the next pages with the changes required highlighted in bold text.
The first change to line 24 sets additional stty parameters to enable Xon/Xoff flow control to function during the course of the lp print job.
The second change at the end of the script restarts the process to enable Xon/Xoff flow control for direct print jobs from Charisma.
This line must be entered before the exit 0 command otherwise it will be ignored.