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G2 PowerPC Core Reference Manual
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MOTOROLA
Implementation-Specific Information
1.3.7
System Interface
The system interface is specific for each processor core implementation.
The G2 core provides a versatile system interface that allows for a wide range of
implementations. The interface includes a 32-bit 60x address bus, a 32- or 64-bit 60x data
bus, and 56 control and information signals (see Figure 1-4). The system interface allows
for address-only transactions, as well as address and data transactions. The core control and
information signals include the address arbitration, address start, address transfer, transfer
attribute, address termination, data arbitration, data transfer, data termination, and core
state signals. Test and control signals provide diagnostics for selected internal circuits.
Figure 1-4. System Interface
The system interface supports bus pipelining, allowing the address tenure of one
transaction to overlap the data tenure of another. The extent of the pipelining depends on
external arbitration and control circuitry. Similarly, the core supports split-bus transactions
for systems with multiple potential bus masters—one device can have mastership of the
address bus while another has mastership of the data bus. Allowing multiple bus
transactions to occur simultaneously increases the available bus bandwidth for other
activity, and as a result, improves performance.
The G2 core supports multiple masters through a bus arbitration scheme that allows various
devices to compete for the shared bus resource. Arbitration logic can implement priority
protocols, such as fairness, and can park masters to avoid arbitration overhead. The MEI
protocol ensures coherency among multiple devices and system memory. Also, the core
on-chip caches, TLBs, and optional second-level caches can be controlled externally.
The core clocking structure allows the bus to operate at integer multiples of the core cycle
time.
G2 Core
1.5 V
Address Arbitration
Transfer Attribute
Address Transfer
Address Start
Clocks
Data Arbitration
Data Termination
Interrupt, Checkstops
Debug Control
JTAG/COP Interface
Processor Status
Output Enable
Input Enable
High-Impedance Control
Data Transfer
Address Termination
Test Interface
Reset
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