12-2
MPC8240 Integrated Processor User’s Manual
Internal Buffers
The MPC8240 supports critical word first burst transactions (double-word aligned) from
the processor core. The CCU transfers this double word of data first followed by double
words from increasing addresses wrapping back to the beginning of the eight-word block,
as required.
Figure 12-1 depicts the organization of the internal buffers.
Figure 12-1.
MPC8240 Internal Buffer Organization
12.1.1 Processor Core/Local Memory Buffers
Because the MPC8240 has a shared internal data bus between the processor and local
memory, for most cases it is unnecessary to buffer data transfers between these devices.
However, there is a 32-byte copyback buffer which is used for temporary storage of the
following:
•
L1 copyback data due to snooping PCI-initiated reads from memory
•
sub-double-word, single-beat writes when read-modify-write (RMW) parity is used
•
processor burst writes when ECC is enabled
The copyback buffer can only be in one of two states—invalid or modified with respect to
local memory. Since the buffer is only used for burst write data, the entire cache line in the
buffer is always valid if any part of the cache line is valid.
Figure 12-2 shows the address and data buffers between the peripheral logic bus and the
local memory bus.
Memory Interface
Control Block
PCI Interface Control Block
Processor/Local Memory
Buffers
PCI/Local Memory
Buffers
Processor/PCI
Buffers
Peripheral Logic Bus Control Block
Summary of Contents for MPC8240
Page 1: ...MPC8240UM D Rev 1 1 2001 MPC8240 Integrated Processor User s Manual ...
Page 38: ...xviii MPC8240 Integrated Processor User s Manual TABLES Table Number Title Page Number ...
Page 48: ...xlviii MPC8240 Integrated Processor User s Manual Acronyms and Abbreviations ...
Page 312: ...6 94 MPC8240 Integrated Processor User s Manual ROM Flash Interface Operation ...
Page 348: ...7 36 MPC8240 Integrated Processor User s Manual PCI Host and Agent Modes ...
Page 372: ...8 24 MPC8240 Integrated Processor User s Manual DMA Register Descriptions ...
Page 394: ...9 22 MPC8240 Integrated Processor User s Manual I2O Interface ...
Page 412: ...10 18 MPC8240 Integrated Processor User s Manual Programming Guidelines ...
Page 454: ...12 14 MPC8240 Integrated Processor User s Manual Internal Arbitration ...
Page 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Page 516: ...16 14 Watchpoint Trigger Applications ...
Page 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
Page 546: ...C 8 MPC8240 Integrated Processor User s Manual ...
Page 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...