Millicode register management and pipeline reset

Abstract

An alternate instruction architecture which uses the preexisting dataflow and hardware controlled execution units of an otherwise conventional pipelined processor to accomplish complex functions. Additional hardware controlled instructions (private milli-mode only instructions) are added to provide control functions or to improve performance. These milli-mode instructions augment the standard 'user visible' architected instruction set (which in the preferred embodiment is the System 390 instruction set). Millicode routines can intermingle the milli-mode only instructions with standard system instructions to implement complex functions. The set of instructions available in milli-mode can be considered to be an alternate architecture that the processor can execute. The millicode and standard system architectures each have there own set of architected registers. However, these registers are dynamically taken from and returned to a common physical register pool under control of a register management system. Provision is also made for communication between the two architectures such that data in the milli-registers and the standard architected registers (such as GPRs) can be exchanged. A set of register operand registers is provided to enable explicit updates of general purpose registers from millicoded routines. Both milli-instructions and standard architecture instructions can be present in the pipeline simultaneously. Provision is thus also made for performing a controlled pipeline reset of the facilities manipulated by the two types of architectures.