Itim Technology Solutions provides an OSDI pack for each of the operating systems it supports. Each OSDI pack contains a number of source files, written in the C programming language. After user modification these files are used to build an OSDI. The OSDI receives device calls from a DP4 application, via the DP4 Terminal Manager.
The OSDI source code can be broadly split into two parts :
Code which provides an interface between the OSDI program and the DP4 Terminal Manager. This code is not intended for user alteration. It is largely operating system dependent and implements the DP4 protocol for Terminal Manager-OSDI communication. It is supplied in object code format so that you can link it with the OSDI module that you modify - the source is provided for information purposes only.
Code to be written by you which provides the interface to the specific hardware that you are accessing. DP4 provides a 'shell' of empty functions in one of the OSDI modules, which you should complete with device-specific code according to the guidelines laid out in this section. The structure of this code is introduced here.
The DP4 Terminal Manager interface code is supplied pre-compiled. After you have modified and compiled the device-specific code it must be linked to produce an executable OSDI.
All output destinations in DP4 are treated as printers, in that any data to be output to them is "printed" from a DP4 DP4 application. This definition is principally one of terminology - you may access any sort of device. Data output to that device may not necessarily be physically printed. For example, you may be using a POD to send control sequences to a robot arm. The control sequences are viewed as printed text by DP4 even though they are not physically printed.