AMD-762 Datasheet, PDF (27/122 Pages) Advanced Micro Devices – System Controller

24416C—December 2001
Preliminary Information
AMD-762™ System Controller Data Sheet
n 33-MHz-only mode that always supports 33-MHz maximum
PCI bus speed. In this mode, the Southbridge and all
downstream PCI agents are clocked from the system clock
generator’s PCI clocks.
The desired PCI clocking mode is selected with the AD[15]
pinstrap on the AMD-762 system controller. Refer to Chapter 7
on page 81 for details of the AMD-762 system controller’s
pinstrapping.
The AMD-762 system controller drives the 64-bit PCI bus
synchronously with the PCI clock. For 32-bit agents, the
AMD-762 system controller converts the 64-bit processor data
to 32-bit PCI data and regenerates commands with minimal
overhead. A processor-to-PCI posted write buffer enables the
processor and PCI to operate concurrently. The AMD-762
system controller converts consecutive processor addresses to
burst PCI cycles. A PCI-to-DRAM posted write buffer and a
DRAM-to-PCI prefetch buffer enable concurrent PCI bus and
processor-DRAM accesses during PCI-initiator transactions.
When the processor drives an I/O cycle to an address other than
the AMD-762 system controller configuration register
addresses, the AMD-762 system controller passes the I/O cycle
to the PCI bus and responds to the CPU only after the PCI
cycle completes. The AMD-762 system controller does not
respond to I/O cycles driven by PCI initiators on the PCI bus.
The AMD-762 system controller allows these cycles to complete
on the PCI bus. A memory write is the only transaction
permitted from PCI to AGP.
The PCI block can be broken up into two sub-blocks—the PCI
target module and the PCI master module. The PCI target
module handles cycles initiated by an external master on the
PCI bus. The AMD-762 system controller responds to cycles
that are directed to main memory or writes that are sent to the
other PCI interface (the AGP interface). This module contains
write buffers (PCI-to-memory and PCI-to-PCI), read buffers
from memory, and a target sequencer that keeps track of the
bus while the AMD-762 system controller is a PCI target.
The PCI master module handles processor-to-PCI bus cycles.
Within a processor stream, no reordering is done.
Chapter 2
Functional Operation
15