Distributing Microcode Patches
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
A peripheral data processing system having a plurality of peripheral devices, such as magnetic tape drives, have a read-only memory (ROM) for sequencing the microprocessor in the peripheral unit. Because of inherent delays in updating a ROM, each peripheral unit has a random-access memory (RAM) which stores patches to the code of the ROM. The RAM is called a patch memory (PM) and is sensed during the execution of the ROM programs by the microprocessor for substituting RAM-stored code patches for the ROM-stored code. Each PM in the peripheral units is updated each time the peripheral system is initially microprogram loaded (IML). A control unit of the peripheral subsystem senses the engineering change (EC) level of all the peripheral units and stores the EC number within the control unit.