Patent GB-1492610-A (GB)
Title: Data equipment for the execution of maintenance operations in an information processing system
IPC: G06F11/22
Filed: 1974-12-19
Abstract: 1492610 Data processing system COMPAGNIE INTERNATIONALE POUR L'INFORMATIQUE 19 Dec 1974 [27 Dec 1973] 55002/74 Heading G4 In a data processing system comprising a plurality of interconnected processing units, each unit includes a diagnostic arrangement comprising a number of shift registers each formed by a hardwired series connection of registers certain ones of which are functional units of the processing unit and the remainder of which copy the contents or state of functional units of the processing unit, and a processing device arranged to control read and write operations in the shift registers and the execution of diagnostic operations in response to locally generated commands or commands received from a common diagnostic unit which is connected for the exchange of data and commands to the diagnostic arrangement in each processing unit. The diagnostic arrangement for a processing unit is shown in Fig. 3 and comprises a microprogram read only store MK addressed by unit MA and reading instructions into register K/AD to control logic unit LU. One of the diagnostic shift registers is formed by the series connection of registers R, forming part of the logic unit, register K/AD, and register LKx which copies the state of unit Kx which is a transfer circuit connecting the logic unit to an external data source. The second diagnostic shift register RDV includes a part E which copies the state of error indicating bi-stables in the logic unit and a part AMK which copies the address output of circuit MA. The registers which are also functional units of the processing unit are hardwire connected in the form of a shift register in addition to their normal connections with the remainder of the processing unit so that switches and other interconnecting devices are not required. The shift registers are circulated, in response to the state of respective control bistables TV, TC controlled by control circuit CG, through multiplexors Mxi and Mxo and register D from where the data is read to or written from the common diagnostic unit via bus LPM. Alternatively each shift register, which may be shifted in either direction, may have an individual register D. Bi-stables ERE and EMO indicate recoverable and non-recoverable errors and when set, cause shift register RDV and shift registers RDV and RDC to be read out respectively. In response to a recoverable error the unit may automatically initiate a recovery routine or may receive such a routine for execution from the common diagnostic unit. The operations in the unit may be interrupted by the common unit and fresh data sent to the unit to re-initialize the unit. As described shift register RDC consists of active units and can only be read out when the unit has been stopped whereas register RDV consists of passive units and may be read out at any time. A further shift register RDS may be provided to receive a set of command data from the common diagnostic unit in a single exchange, e.g. to control a local peripheral unit such as a tape reader. Register RDS contains a counter to enable a required number of operations to be performed before the unit returns to normal operations. The common diagnostic unit is connected to the central processor unit from where it may obtain programs &c. and may be connected to another source such as a further central processor and/or a magnetic tape unit.