APPENDIX A
SYSTEM OBJECT STRUCTURES
The object structures of Interface Processors are described belOil. The only objects structures described are for those whose form or interpretation differ fran GOP object structures. Note that the values found in the length fields in the var ious objects descr ibed belOil are encoded as "actual length minus 1" in bytes. Also note that the object indices refered to below are of the same format as object selectors with the entry access segment index subfield uninterpreted. The displacement subfield is interpreted as an index into the associated domain access segment.
In the Trost general terms, contexts for Interface Processors and General Data Processors serve the same purpose. They are used to represent an access environment in which process execution can take
place. On closer inspection, hCMever, the differences are significant. For example, with Interface Processors there is no concept of a sequential instruction stream. Instead the only instructions executed by Interface Processors are functions requested, one at a t:ime, by software executing on the associated Attached Processor. At a mundane level, this means that Interface Processor contexts need not provide access to instruction segments or operand stacks. More significantly, without a sequential instruction stream there are no concepts of intracontext or intercontext control flow either. This results in the binding between Interface Processor processes and contexts being static. In fact, context access and data segments are refinements of the corresponding process access and data segments respectively.
Given these differences, an Interface Processor context represents the access environment available within the 432 system to the logical process being executed on the logical processor comprised of the Interface Processor and the associated Attached Processor. The operators provided by the Attached Processor affect the contents of data segments in this environment via the address mapping facility of the Interface Processor. The operators provided by the Interface Processor affect this environment via the function request facility of the Interface Processor.
