Structured control instruction fetch unit

摘要

The structured control instruction fetch unit is a structured instruction stream controller that processes expand (XP), expand register indirect (XPR), loop (LOOP), and break (BRK) instructions for structured control. The fetch unit processes stop bits that mark the end of instruction blocks. Any instruction can be marked with a stop bit to indicate that it is the last one in an instruction block. All instructions are encoded with a predicate to reduce the use of control instructions and to simplify the control. A control stack guides instruction fetching by storing return addresses, loop block addresses, loop predicates, and loop counters. Control instructions and stop bits manage operation of the control stack. An instruction unit feeds execution units and includes a set-associative instruction cache, a control stack, an instruction buffer that decouples instruction fetching from execution, instruction decoders, and program counter (PC) control logic.

主权项

1. A structured control instruction fetch unit, comprising:
a stack controller; a control stack having an address stack and a counter stack, the stack controller managing the control stack; and execution units in operable communication with the control stack; wherein the structured control instruction fetch unit is configured for processing fixed format block structured instructions, the fixed format block structured instructions having a control instruction including a predicate field, an opcode field, an offset field, and a stop field, the instructions being processes via the control stack, the stack controller feeding the fixed format block structured instructions to the execution units, the execution units executing blocks of the instructions based on the content of the predicate, opcode, offset, and stop fields, the execution units terminating execution of the instruction blocks upon reading stop bits in the stop fields; and wherein the instruction blocks are executed by the execution units in direct correspondence with blocks of high-level code, the structured control instruction fetch unit implementing loops and nested block expansions without the necessity of low level branch and jump instructions.