AMD-762 Advanced Micro Devices, AMD-762 Datasheet - Page 31

• Manufacturer Part Number: AMD-762
• Description: System Controller
• Manufacturer: Advanced Micro Devices

24416C—December 2001
2.3.5
2.4
Chapter 2
Accelerated Graphics Port (AGP)
PCI Accesses by an Initiator
A P C I i n i t i a t o r b egins a me mor y r e ad or writ e cycle by
asse rting FRAME# and pla c in g t h e m e m o ry a dd r e ss on
AD[31:00] (note that the AMD-762 system controller supports a
maximum a dd ress spa ce of 32 bits). The AMD-762 system
controller decodes the address. If the address is within the
m e m o ry re gion as d e f i n e d by PCI Top of Me m o ry (Dev
0:F0:0x9C), the AMD-762 system controller accepts the cycle
and responds as a PCI target by asser t ing DEVSEL#. If the
address is not within the defined memory region, the AMD-762
system controller ignores the cycle and allows it to complete on
the PCI.
Read requests from PCI masters to the memory subsystem are
full cache lines only. After fetching the initial cache line, the
AMD-762 system controller can optionally start prefetching the
next cache line. Prefetching the next cache line is preferred,
because the PCI master typically reads more than one line, but
can waste DRAM bandwidth if this line is thrown away.
The length of a read request is always 8 quadwords (one cache
line). During writes, the AMD-762 system controller attempts
to accumulate an entire cache line. If the start address is not
cache aligned, the AMD-762 system controller makes single
write requests until it reaches a cache-aligned address. When
aligned, it makes a request every 8 quadwords. If a partial
cache line write is detected, no more data is accumulated, and
a request is issued to the memory subsystem.
Th e Acce l e ra ted Gra p h i cs Por t (AGP) is a poin t-to-p oint
connection between a graphics adapter (AGP initiator) and the
AMD-762 system controller memory controller (AGP target),
which enables the adapter to store and use graphics data in
main memory. This connection relieves graphics traffic from
the PCI bus and greatly accelerates video performance.
The AMD-762 system controller functions as an AGP target,
providing all the signals, buffers, and logic required for full
complia n ce wit h t h e Accelerat ed Graphics Port Interface
Specification, Revision 2.0.
Preliminary Information
Functional Operation
AMD-762™ System Controller Data Sheet
19