Patent GB-1425173-A (GB)
Title: Data processing systems
IPC: G06F13/24
Filed: 1972-05-03
Abstract: 1425173 Interrupt arrangements GENERAL ELECTRIC CO Ltd 2 May 1973 [3 May 1972] 20596/72 Heading G4A A data processing system including at least one processor P0, P1 (Fig. 1) and input-output channels CH0, CH1 connected to a plurality of peripherals includes an interrupt arrangement connected to at least one of the input/output channels and comprising two duplicate units D0, D1, each consisting of storage elements 200 (Fig. 2) for storing interrupt requests from the peripherals, control logic circuitry 208 responsive to instructions from the processor to read out the contents of a selected storage element for transmission to the processor and a comparator 210 which compares the contents of like elements in each of the stores 200 to derive an error signal in the event of disparity, the control logic circuitry being responsive to further instructions from the processor to perform test operations on the stores to lock out any faulty storage elements.  As described two channels are connected to the interrupt arrangement. Each store 200 comprises 16 groups of 16 elements, one group being shown in Fig. 3 and consisting of 16 primary and 16 secondary bi-stable toggles 4, 5 read out via gates 22 when the group is selected by an address signal at level " 0 " at terminal 21. The outputs of pairs of toggles associated with peripherals requiring an immediate interrupt of processor are strapped to a bus 28 to provide a local interrupt signal on terminal 30 to input terminal 31 of the other duplicate when a lock out toggle 24 is not set. Either the local interrupt signal, or if the toggle 24 is set an incoming interrupt signal, is fed via OR gate 41 to terminal 44. Control logic circuitry (Figs. 4A, 4B, 4C, not shown).-One of the channels is selected by applying the appropriate address on to an upper byte address highway, the lower byte address highway, normally used for selecting a peripheral, being used in the channels associated with interrupt circuitry to transmit an instruction. The parity of this byte is checked and combined with the parity check bit from the upper and lower data bytes to derive an enabling signal for gates in the control circuitry. The most significant bit 7 indicates whether the operation is to be a test or normal load. Bits 5, 6 select one of the two duplicates and bits 0-3 are decoded in a decoder (60) to provide a " zero " signal on one of 10 lines to 10 toggles (T0-T9) controlling inter alia the reading out of the storage toggles 4, 5 (Fig. 3) the setting and resetting of the lock out toggle 24 and the setting of a partition toggle which is set in one duplicate when the other duplicate is found to be faulty. A gate (81) is enabled by a " load suspended priority register " instruction to clock a register (100, Fig. 5, not shown) receiving 4-bit data representing the priority of the head of a suspended process queue. This is added to the four bit priority of the lowest priority process being currently run and if the waiting process priority is the greater an immediate interrupt signal is applied, after a persistence check, to one of the " immediate interrupt " inputs of the store 200. A gate (82) is enabled by a " freeze, read, reset " instruction to supply a signal on lead 10 (Fig. 2) to hold the contents of toggles 5, followed by a read signal, followed by a resetting signal for the toggles 4. Determination of lowest priority.-Logic circuitry (Fig. 6, not shown) determines which of the two processors P0, P1 is running the lower priority process by examining the bits of the priority data to determine the most significant bit in which the data differs to derive a signal if processor P1 has a " 1 " in that bit position. This signal controls two sets of gates (130, 131) to feed out the lower priorty data to the adder of Fig. 5. Duplicate selector circuits.-Data from interrupt data bus 209 (Fig. 2) of one of the duplicates is selected under the control of logic circuitry DS0, DS1 (Fig. 1). The lower bytes from each duplicate are fed to AND gates (160, 161, Fig. 8A, not shown) in each of the selectors. Bits 0-3 of the lower address byte are decoded in a decoder (163, Fig. 8B, not shown) to provide a " 0 " signal on one of four outputs, two of which control the locking out of the duplicate by controlling a toggle (165), one of which resets the toggle (165) and one of which provides an enabling signal for gates (180-184) to read out the states of toggles in the system. Similar circuitry processes the upper data byte.