Browse Prior Art Database

Improved L2 Cache Interface through use of Early Transfer

IP.com Disclosure Number: IPCOM000118072D
Original Publication Date: 1996-Sep-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Milling, PE: AUTHOR

Abstract

Disclosed is a method for improving the performance of systems with L2 caches through the use of an Early Transfer Acknowledge (ETA) signal. The memory controller asserts the ETA signal one clock cycle before it asserts the Transfer Acknowledge (TA) signal.

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Improved L2 Cache Interface through use of Early Transfer

      Disclosed is a method for improving the performance of systems
with L2 caches through the use of an Early Transfer Acknowledge (ETA)
signal.  The memory controller asserts the ETA signal one clock cycle
before it asserts the Transfer Acknowledge (TA) signal.

      For cpu read cycles, the memory controller asserts the TA
signal when the read data is valid.  For cpu write cycles, the memory
controller asserts the TA signal when it accepts the write data.  The
L2 cache controller can use the ETA signal to allow it assert control
signals such as Burst Address Advance (BAA) to the synchronous burst
static Random Access Memories (RAMs) which are used to store the
cache data.

      For a L2 castout when the L2 cache needs to write out a
modified cache line, the L2 cache controller asserts BAA during each
clock cycle that the memory controller asserts TA allowing a n-1-1-1
transfer rate as is illustrated in Fig. 1.  The L2 cache controller
uses the ETA input signal to time when to assert the BAA signal.
Without the ETA signal, the look-aside L2 cache controller would cast
out data at a n-2-2-2 transfer rate as in Fig. 2.

      For Fig. 1 and Fig. 2, TS# means Transfer Start, DOE# means
Static RAM (SRAM) Data Output Enable, DWE# means SRAM Data Write
Enable, TA# means Transfer Acknowledge, ETA# means Early Transfer
Acknowledge.  A signal name which has "#" as its last character means
that the si...