Browse Prior Art Database

Virtual Line Buffer

IP.com Disclosure Number: IPCOM000100070D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 54K

Publishing Venue

IBM

Related People

Chang, JH: AUTHOR [+2]

Abstract

Disclosed is a Line Buffer (LB) access scheme for fast accessing to/ from the LB in a cache system. The virtual address, instead of the real address, of the line in the LB is used for fast access.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 57% of the total text.

Virtual Line Buffer

       Disclosed is a Line Buffer (LB) access scheme for fast
accessing to/ from the LB in a cache system.  The virtual address,
instead of the real address, of the line in the LB is used for fast
access.

      On a cache miss, a cache line is fetched from the main memory.
When the first DW (Double Word) arrives, it will be passed to the CPU
(Central Processing Unit) while the rest of the line is loaded into a
LB.  A LB is used for buffering the incoming line while the CPU can
continue accessing the cache.  The LB can be emptied either on free
cache cycles or simply at the next cache miss.  Due to access
locality, both temporal and spatial, direct accesses of a partially
loaded line are also important for improving the cache performance.
To allow directed accesses from LB, the LB is tagged with the line
address and DW valid bits.  For a conventional implementation, the
real line address is used as the tag, then it is necessary to wait
until the completion of the address translation before it can be
decided whether the content of the LB or the cache array are to be
accessed by the CPU.  Thus cycle time will be longer, especially when
there is a chip-crossing between the address translation hardware and
the LB.

      A virtual LB has both virtual and real address tags. The
virtual address and the DW valid bits are used to decide whether or
not the content in the LB are to be sent to the CPU during a
fetch access.  If the virtual addre...