GT-64260A Design Guide
Doc. No. MV-S300165-00, Rev. A
CONFIDENTIAL
Copyright © 2002 Marvell
Page 18
Document Classification: Proprietary Information
May 21, 2002, Preliminary
On the 60x bus, the internal 60x master supports snoop and master capability for data transfers between the GT-
64260A and other agents on the 60x bus, such as another GT-64260A device.
3.3
MPX Bus Mode
Note
The GT-64260A does not support multi-GT mode in MPX bus mode.
The GT-64260A can act as master and slave on the MPX bus. In this mode, the GT-64260A 60x internal arbiter
supports two masters on the bus, one external MPX compatible master and the internal CPU bus master for
snoop transaction only. The GT-64260A is configured to MPX bus mode by AD[7:6] signals sampled to b’01’ at
reset de-assertion. The CPU bus configuration can be read in the CPU Mode Register (Offset: 0x120) bits CPU-
Type (bits 7:4).
describes the MPX bus features that are supported by the GT-64260A.
3.4
Cache Coherency
The GT-64260A supports full cache coherency between the SDRAM and CPU caches.
Any access to the SDRAM (from PCI or IDMA) may result in a snoop transaction driven by the GT-64260A on the
CPU bus. The SDRAM access to a cache coherent region is always suspended until the snoop is resolved. In
case of a HIT in a modified line in CPU cache, the SDRAM access might be suspended until the line write-back to
SDRAM is completed.
describes the transaction flow for PCI reads from cache coherent regions.
Table 2:
GT-64260A Supported Features in MPX Bus Mode
Features Description
Address streaming
The CPU initiates a new address tenure the cycle after AACK* assertion without a
dead cycle between the two address tenures.
Data streaming
If the data bus is driven by the same agent in both data tenures, no dead cycle is
required between two consecutive data tenures.
16 byte burst
Load/store of AltiVec uncached operands.
Read out of order
completion
The CPU read response data of pipelined transactions in any order. The DTI[0-2] pins
indicates data tenure ID.
•
000 = data of the oldest pending read.
•
001 = the second oldest pending read.
•
010 = the third oldest pending read.
NOTE:
To enable the read out of order completion, the CPU Configuration register’s
RdOOO
bit [16] and
Pipeline
bit [13] must be set to ‘1’, at offset 0x000.