Honeywell Information Systems Inc.

Allen C Hirtle

Gary J Goss

David B O'Keefe

A communication multiplexer stores the receive and transmit channel numbers of input/output devices coupled to the multiplexer by communication lines in a first-in-first out (FIFO) memory. The input/output devices are polled by sending the channel numbers from the FIFO to the input/output devices. An input/output device requesting service responds to its channel number. The remaining channel numbers in the FIFO are recirculated to give the receive channel numbers priority over the transmit channel numbers. This gives high priority to a most recently used receive channel operative in a burst mode and equal priority to all transmit channels.

Communication multiplexer variable priority scheme

A data processing system includes means which are operative when the system is conditioned for operating in a trace mode during the processing of program instructions, to record the op code of each instruction designated as executable by the bit contents of a table referenced before beginning instruction execution. When the op code of an instruction is designated by the table as not being executable, the system traps the instruction and generates a call to the operating system software without recording its op code. The selective recording and trapping of instruction operation codes facilitates diagnosis of program errors or faults within the system. This is particularly valuable when the system includes emulation apparatus which may not be completely compatible in every detail with the system being emulated.

Trace method and apparatus for use in a data processing system

A processing unit includes emulation apparatus which operates to execute instructions of a target system, one of a plurality of ways depending upon the options and features of the target system being emulated. The options, features and characteristics of the target system for which the program was originated is defined by the different bits of an option mask word stored within the emulation apparatus. Initially, upon switching to an emulation mode of operation, the emulation apparatus under microprogram control is operative to store signal representations of the option mask word in one of its storage registers. The signals from the stored option mask word are applied to different portions of the emulation apparatus for conditioning the apparatus to execute target system program instructions in accordance with the structural characteristics of the target system for which the program was originated.

Emulation apparatus

A host system includes a plurality of memory cells, each reserved for a different one of a plurality of peripheral control devices of a target system. During the running of a target system program, the host system being emulated includes means for switching one of the memory cells reserved for a particular peripheral control upon detection of an interrupt condition resulting from the execution of a target system input/output instruction. Each time an interrupt condition causes the switching of one of these cells, the host system increments by one the contents of a counter representative of a bus present in the target system. Each time one of the cells of a bus is reset or cleared, the host system decrements by one the corresponding counter contents. A count of zero stored in the counter simulates the condition of a binary ZERO of providing a logical OR operation upon all of the interrupt signals of the peripheral devices connected to share the same target system bus while a non zero count stored in the counter simulates a binary ONE of performing a logical OR operation upon the interrupt signal lines on the bus.

Emulation of target system interrupts through the use of counters

A host microprogrammed data processing system includes a plurality of tables to store information coded to define a plurality of a variety of different input-output system configurations of resources required to execute input-output instructions in a corresponding number of target systems being emulated by the host system. The host system further includes emulation apparatus which includes a control store which stores microprograms for directing the system in processing input-output instructions of target programs and for verifying whether each such instruction can be executed by the host system. The emulation apparatus generates coded information indicating which one of a given number of channel program routines the host system is required to use to execute the input-output instruction using the host input-output resources. Using the information of the tables, the emulation apparatus is able to execute completely certain types of target system input-output instructions used to perform control operations.

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Needham, MA, United States of America

Allen C Hirtle