GB1443176A - Data processor control of a plurality of devices - Google Patents

Abstract

1443176 Data processing INTERNATIONAL COMPUTERS Ltd 11 April 1974 [13 April 1973] 17865/73 Heading G4A In a data processing system a system manager program 10, when in control of the processor, issues commands to device manager programs 11, 12, and when control has been passed to a device manager for execution of a command the device manager supervises the operation of an associated one or more peripheral devices and control is passed from each device manager to the next in a predetermined cyclic sequence without return to the system manager until one of the device managers detects that execution of a command issued to it has been terminated. Control may be passed between device managers by including in each the start address of the next manager in the sequence, but immediate return to the system manager after setting-up a command may be caused by including a qualifier bit in the command code. Alternatively control may be passed between device managers using a table of device manager start addresses accessed sequentially by the device managers, the table being set up by the system manager or other software. The system manager 10 issues a command to a device manager 11, 12 by causing a jump to the entry point of the device manager and storing the command code and a return link address in two reserved registers. A device manager returns control to the system manager, when execution of its command has been terminated, by adding 0, 4 8 or 12 to the link address, depending on the the reason for the return, the modified link address storing a GO TO instruction pointing to the appropriate system manager routine. Device managers include a routine for each command: TRANSFER (specified number of characters into specified buffer area), DEMAND STATUS (software state of device manager and address of a first word in a set indicating the hardware state of the peripheral to be transferred to the system manager), SET MODE (set or unset peripheral in autonomous or slave mode), DEALLOCATE (disconnect peripheral from processor), RESET; and a MONITOR routine which checks for conditions requiring return to the system manager. Normal level operations round the device manager sequence loop 20 are interspersed with interrupt operations concerned with transfer of characters between peripherals and the buffer area. Each device manager may also enter the system manager as a conceptual routine, e.g. to cause print-out of a message at an operator console to indicate that a particular peripheral device should be connected into the system, the console being treated as a peripheral device and having its own device manager program in the sequence loop 20.