GB1441444A - Logging the sequence of a programme in data processing systems - Google Patents

Abstract

1441444 Monitoring data processing systems INTERNATIONAL BUSINESS MACHINES CORP 30 Aug 1973 [23 Sept 1972] 40774/73 Heading G4A A record of a sequence of instructions executed in a data processing system is made by recording the store address of executed instructions in a selected one of the following three modes, viz. recording for each branch instruction in which the branch is taken only the "branch-to" address, for each branch instruction in which the branch is taken the "branch-to" and branch from addresses, and the address of each executed instruction. The system which is monitored consists of a microprogram control word store 4 addressed by register 3 in response to signals from the previous address incrementer 1, the output register 9 in the case of branch instructions specifying a "branch-to" instruction address, and lines TRAP and TLU supplying interrupt instruction addresses. A mode switch 17 causes the relevent instruction addresses to be stored in store 19 in response to mode-control signals. The store includes 16 locations which are addressed cyclically so that at any time the store contains a log of the most recently executed part of the program. A gating network is described, Fig. 4 (not shown), to fulfill the function of mode switch 17. The network provides a write signal to store the contents of address register 3 in each machine cycles. The network also provides "advance" signals to increment address counter 18 to address the next storage location in store 19 when the contents of address register 3 are to be retained, e.g. in mode 3 in every cycle. Mode 3 operation may be used for retry purposes when an error occurs. The record stored in store 19 may be printed out.