12-6
MPC8240 Integrated Processor User’s Manual
Internal Buffers
previously latched data. Store gathering is only used for writes to PCI memory space not
for writes to PCI I/O space. The store gathering continues until the buffer is scheduled to
be flushed or until the processor issues a synchronizing transaction.
For example, if both PRPWBs are empty and the processor issues a single-beat write to
PCI, the data is latched in the first buffer and the PCI interface of the MPC8240 requests
mastership of the PCI bus for the transfer. The data for the next processor-to-PCI write
transaction is latched in the second buffer, even if the second transaction’s address falls
within the same half cache line as the first transaction. While the PCI interface is busy with
the first transfer, any sequential processor single-beat writes within the same half cache line
as the second transfer are gathered in the second buffer until the PCI bus becomes available.
12.1.3 PCI/Local Memory Buffers
There are four data buffers for PCI accesses to local memory—two 32-byte PCI-to-local
memory read buffers (PCMRBs) for PCI reads from local memory and two 32-byte
PCI-to-local memory write buffers (PCMWBs) for PCI writes to local memory.
Figure 12-4 shows the address and data buffers between the PCI bus and the local memory.
Figure 12-4. PCI/Local Memory Buffers
Note that many PCI accesses to local memory are snooped on the peripheral logic bus to
ensure coherency between the PCI bus, local memory, and the L1 cache of the processor.
All snoops for PCI accesses to local memory are performed strictly in order.
PCI Address/Data
PCI/Memory
Write Buffers
Processor Address/Control
Processor/Memory Data
Memory Row/Column Address
A
D0 D1 D2 D3
A
D0 D1 D2 D3
A
D0 D1 D2 D3
PCI/Memory
Read Buffers
(PCMWBs)
(PCMRBs)
A
D0 D1 D2 D3
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 ...