MULTI-PROGRAMMING DATA PROCESSING SYSTEM PROCESS SUSPENSION

摘要

MULTI-PROGRAMMING DATA PROCESSING SYSTEM PROCESS SUSPENSION Each process in a multi-process computing system using so-called capabilities may have associated with it a process dumpstack protected by the capability mechanism. The functions of this dumpstack are (i) to provide the state of the process at the point at which it was suspended and (ii) to stack (or nest) information relating to the invoked procedures (i.e. sub-routines) of the process. Thus there is a fixed sized portion containing principally the machine registers, the indicators and the watchdog timer values and a variable sized portion containing information related to each nested procedure. Each stack link is of fixed size and contains three items:- relativised instruction address, the code block capability and process capability pointer list block capability. This arrangement is enhanced to allow two additional classes of information to be stored in each link namely (a) an indication of the data and capability registers preserved during the domain change procedure and (b) descriptors for local storage segments. The use of descriptors for local storage allows a pool of storage particular to the process to be allocated on a segmented basis with the security of the capability mechanism extended into that local storage area. The descriptors for local storage segments resemble closely SCT entries (i.e. they contain sumcheck, base and limit values) and they are relative to a new protected stack, the local store stack, which is referenced by a hidden capability register C(L). The processor module is provided with a new instruction "subset local store" for use in local store segment allocation and - ii automatic de-allocation occurs when a return is made from the procedure in which the local segment was allocated. Such allocation and de-allocation mechanisms use the indications which takes the form of a primary descriptor held in the most sigificant eight bits of the IAR word. This descriptor is allocated as follows:- (i) zero, no stacked registers or local segments allocated, (ii) m.s.b. = 1, stacked registers to be passed and (iii) l.s.b. 1-7 = 1, indicates the number of local store segments allocated. Associated with the stacked register set is a one word descriptor which indicates the registers stacked.