NAME

cpu — HP PA-RISC CPU

SYNOPSIS

cpu* at mainbus0 irq 31

DESCRIPTION

The following table lists the PA-RISC CPU types and their characteristics, such as TLB, maximum cache sizes (where the ‘*’ character means on-chip) and HP 9000/700 machines they were used in (see also intro(4) for the reverse list).

FLOATING-POINT COPROCESSOR

The following table summarizes available floating-point coprocessor models for the 32-bit PA-RISC processors.

SUPERSCALAR EXECUTION

The following table summarizes the superscalar execution capabilities of 32-bit PA-RISC processors.

In conclusion, all of the above CPUs are dual-issue, or 2-way superscalar, with the exception that on CPUs with two integer ALUs only one of these units is capable of doing shift, load/store and test operations. Additionally, there are several kinds of restrictions placed upon the superscalar execution:

For the purpose of showing which instructions are allowed to proceed together through the pipeline, they are divided into classes:

For CPUs with two integer ALUs (7100LC, 7200, 7300LC), the following table lists the instructions which are allowed to be executed concurrently:

ldst + ldst is also possible under certain circumstances, which is then called "double word load/store".

The following restrictions are placed upon the superscalar execution:

• An instruction that modifies a register will not be bundled with another instruction that takes this register as operand. Exception: a flop can be bundled with an FP store of the flop's result register.
• An FP load to one word of a doubleword register will not be bundled with a flop that uses the other doubleword of this register.
• A flop will not be bundled with an FP load if both instructions have the same target register.
• An instruction that could set the carry/borrow bits will not be bundled with an instruction that uses carry/borrow bits.
• An instruction which is in the delay slot of a branch is never bundled with other instructions.
• An instruction which is at an odd word address and executed as a target of a taken branch is never bundled.
• An instruction which might nullify its successor is never bundled with this successor. Only if the successor is a flop instruction is this bundle allowed.

PERFORMANCE MONITOR COPROCESSOR

The performance monitor coprocessor is an optional, implementation-dependent coprocessor which provides a minimal common software interface to implementation-dependent performance monitor hardware.

DEBUG SPECIAL UNIT

The debug special function unit is an optional, architected SFU which provides hardware assistance for software debugging using breakpoints. The debug SFU is currently defined only for Level 0 processors.

SEE ALSO

asp(4), intro(4), lasi(4), mem(4), pdc(4), wax(4)

Hewlett-Packard, PA-RISC 1.1 Architecture and Instruction Set Reference Manual, May 15, 1996.

Hewlett-Packard, PA7100LC ERS, Public version 1.0, March 30 1999.

Hewlett-Packard Journal, Design of the PA7200 CPU, February 1996.

Hewlett-Packard, PA7300LC ERS, Version 1.0, March 18 1996.

HISTORY

The cpu driver was written by Michael Shalayeff <mickey@openbsd.org> for the HPPA port for OpenBSD 2.5.