Freescale Semiconductor MPC8260 Chapter 8 The 60x Bus

MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 8-1
Chapter 8
The 60x Bus
The 60x bus, which is used by processors that implement the PowerPC architecture, provides flexible
support for the on-chip MPC603 processor as well as other internal and external bus devices. The 60x bus
supports 32-bit addressing, a 64-bit data bus, and burst operations that transfer as many as 256 bits of data
in a four-beat burst. The 60x data bus can be accessed in 8-, 16-, 32-, and 64-bit data ports. The 60x bus
supports accesses of 1, 2, 3, and 4 bytes, aligned or unaligned, on 4-byte (word) boundaries; it also supports
64-, 128-, 192-, and 256-bit accesses.
The address and data buses support synchronous, one-level pipeline transactions. The 60x bus interface
can be configured to support both external and internal masters or internal masters only.
8.1 Terminology
Tabl e 8-1 defines terms used in this chapter.
Table8-1. Terminology
Term Definition
Atomic A bus access that attempts to be part of a read-write operation to the same address uninterrupted
by any other access to that address. The PowerQUICCII initiates the read and write separately, but
signals the memory system that it is attempting an atomic operation. If the operation fails, status is
kept so that PowerQUICCII can try again.
Beat A single state on the PowerQUICCII interface that may extend across multiple bus cycles. (An
PowerQUICCII transaction can be composed of multiple address or data beats.)
Burst A multiple-beat data transfer whose total size is typically equal to a cache block size (in
PowerQUICCII: 32 bytes, or 4 data beats at 8 bytes per beat).
Cache block The PowerPC architecture defines the basic unit of coherency as a cache block, which can be
considered the same thing as a cache line.
Clean An operation that causes a cache block to be written to memory if modified, and then left in a valid,
unmodified state in the cache.
Flush An operation that causes a cache block to be invalidated in the cache, and its data, if modified, to
be written back to main memory.
Kill An operation that causes a cache block to be invalidated in the cache without writing any modified
data to memory.
Lane A sub-grouping of signals within a bus. An 8-bit section of the address or data bus may be referred
to as a byte lane for that bus.
Master The device that owns the address or data bus, the device that initiates or requests the transaction.
Modified Identifies a cache block The M state in a MESI or MEI protocol.