AMD-762JLC AMD [Advanced Micro Devices], AMD-762JLC Datasheet - Page 31

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

24416C—December 2001
2.3.5
2.4
Chapter 2
Accelerated Graphics Port (AGP)
PCI Accesses by an Initiator
A PCI initiator begins a memory read or write cycle by
asserting FRAME# and placing the memory address on
AD[31:00] (note that the AMD-762 system controller supports a
maximum address space of 32 bits). The AMD-762 system
controller decodes the address. If the address is within the
memory region as defined by PCI Top of Memory (Dev
0:F0:0x9C), the AMD-762 system controller accepts the cycle
and responds as a PCI target by asserting 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.
The Accelerated Graphics Port (AGP) is a point-to-point
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
compliance with the Accelerated Graphics Port Interface
Specification, Revision 2.0.
Functional Operation
AMD-762™ System Controller Data Sheet
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