7-12
MPC8240 Integrated Processor User’s Manual
PCI Bus Protocol
7.3.3.1 Memory Space Addressing
For memory accesses, PCI defines two types of burst ordering controlled by the two
low-order bits of the address—linear incrementing (AD[1:0] = 0b00) and cache wrap mode
(AD[1:0] = 0b10). The other two AD[1:0] possibilities (0b01 and 0b11) are reserved.
As an initiator, the MPC8240 always encodes AD[1:0] = 0b00 for PCI memory space
accesses. As a target, the MPC8240 executes a target disconnect after the first data phase
completes if AD[1:0] = 0b01 or AD[1:0] = 0b11 during the address phase of a local
memory access. See Section 7.4.3.2, “Target-Initiated Termination,” for more information
on target disconnect conditions.
For linear incrementing mode, the memory address is encoded/decoded using AD[31:2].
Thereafter, the address is incremented by 4 bytes after each data phase completes until the
transaction is terminated or completed (a 4-byte data width per data phase is implied). Note
that the two low-order bits on the address bus are included in all parity calculations.
For cache wrap mode (AD[1:0] = 0b10) reads, the critical memory address is decoded
using AD[31:2]. The address is incremented by 4 bytes after each data phase completes
until the end of the cache line is reached. For cache-wrap reads, the address wraps to the
beginning of the current cache line and continues incrementing until the entire cache line
(32 bytes) is read. The MPC8240 does not support cache-wrap write operations and
executes a target disconnect after the first data phase completes for writes with
AD[1:0] = 0b10. Again, note that the two low-order bits on the address bus are included in
all parity calculations.
7.3.3.2 I/O Space Addressing
For PCI I/O accesses, all 32 address signals (AD[31:0]) are used to provide a byte address.
After a target has claimed an I/O access, it must determine if it can complete the entire
access as indicated by the byte enable signals. If all the selected bytes are not in the address
range of the target, the entire access cannot complete. In this case, the target does not
transfer any data and terminates the transaction with a target-abort error. See
Section 7.4.3.2, “Target-Initiated Termination,” for more information.
Table 7-3. Supported Combinations of AD[1:0]
AD[1:0]
MPC8240 as Target
MPC8240 as Initiator
Read
Write
Read
Write
00
Linear
√
√
√
√
01
reserved
TD
TD
—
—
10
Cache wrap
√
TD
—
—
11
reserved
TD
TD
—
—
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 ...