
MOTOROLA
Chapter 1. Overview
1-31
Implementation-Specific Information
1.3.5
Memory Management
The following sections describe the memory management features of the PowerPC
architecture and the G2 core implementation, respectively.
1.3.5.1
PowerPC Memory Management
The primary functions of the MMU are to translate logical (effective) addresses to physical
addresses for memory accesses and to provide access protection on blocks and pages of
memory.
The core generates two types of accesses that require address translation—instruction
accesses and data accesses to memory generated by load and store instructions.
The PowerPC MMU and exception model support demand-paged virtual memory. Virtual
memory management permits execution of programs larger than the size of physical
memory; demand-paged implies that individual pages are loaded into physical memory
from system memory only when they are first accessed by an executing program.
The hashed page table is a variable-sized data structure that defines the mapping between
virtual page numbers and physical page numbers. The page table size is a power of two, and
its starting address is a multiple of its size.
The page table contains a number of page table entry groups (PTEGs). A PTEG contains
eight page table entries (PTEs) of 8 bytes each; therefore, each PTEG is 64 bytes long.
PTEG addresses are entry points for table search operations.
Address translations are enabled by setting bits in the MSR—MSR[IR] enables instruction
address translations and MSR[DR] enables data address translations.
1.3.5.2
Implementation-Specific Memory Management
The instruction and data memory management units in the G2 core provide 4 Gbytes of
logical address space accessible to supervisor and user programs with a 4-Kbyte page size
and 256-Mbyte segment size. Block sizes range from 128 Kbytes to 256 Mbytes and are
Instruction
address
breakpoint
01300
An instruction address breakpoint exception occurs when the address (bits 0–29)
in the IABR matches the next instruction to complete in the completion unit, and
IABR[bit 30] is set.
System
management
interrupt
01400
A system management interrupt is caused when MSR[EE] = 1 and the core_smi
input signal is asserted.
Reserved
01500–02FFF —
Table 1-4. Exceptions and Conditions (continued)
Exception Type
Vector Offset
(hex)
Causing Conditions
F
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