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B-6
MPC8240 Integrated Processor User’s Manual
Little-Endian Mode
Note that munging makes individually aligned scalars appear to the processor as stored in
little-endian byte order when, in fact, they are stored in big-endian order but at different
byte addresses within double words. Only the address is modified not the byte order.
The munged address is used by the memory interface of the MPC8240 to access local
memory. To provide true little-endian byte-ordering to the PCI bus, the MPC8240
unmunges the address to its original value and the byte lanes are reversed. The MPC8240
unmunges aligned addresses by XORing the three low-order address bits with a three-bit
value that depends on the length of the operand (1, 2, 3, 4, or 8 bytes), as shown in Table
B-3.
The MPC8240 also supports misaligned 2-byte transfers that do not cross word boundaries
in little-endian mode. The MPC8240 XORs the address with 0x100. Note that the
MPC8240 does not support 2-byte transfers that cross word boundaries in little-endian
mode.
The byte lane translation for little-endian mode is shown in Table B-4.
Table B-2. Processor Address Modification for Individual Aligned Scalars
Data Length
(in Bytes)
Address Modification
A[29–31]
8
No change
4
XOR with 0b100
2
XOR with 0b110
1
XOR with 0b111
Table B-3. MPC8240 Address Modification for Individual Aligned Scalars
Data Length
(in Bytes)
Address Modification
A[29–31]
8
No change
4
XOR with 0b100
3
XOR with 0b101
2
XOR with 0b110
1
XOR with 0b111
Table B-4. Byte Lane Translation in Little-Endian Mode
Processor
Byte Lane
Processor Data Bus
Signals
PCI Byte Lane
PCI Address/Data Bus
Signals During PCI Data
Phase
0
DH[0–7]
3
AD[31–24]
1
DH[8–15]
2
AD[23–16]
2
DH[16–23]
1
AD[15–8]
3
DH[24–31]
0
AD[7–0]
Содержание MPC8240
Страница 1: ...MPC8240UM D Rev 1 1 2001 MPC8240 Integrated Processor User s Manual ...
Страница 38: ...xviii MPC8240 Integrated Processor User s Manual TABLES Table Number Title Page Number ...
Страница 48: ...xlviii MPC8240 Integrated Processor User s Manual Acronyms and Abbreviations ...
Страница 312: ...6 94 MPC8240 Integrated Processor User s Manual ROM Flash Interface Operation ...
Страница 348: ...7 36 MPC8240 Integrated Processor User s Manual PCI Host and Agent Modes ...
Страница 372: ...8 24 MPC8240 Integrated Processor User s Manual DMA Register Descriptions ...
Страница 394: ...9 22 MPC8240 Integrated Processor User s Manual I2O Interface ...
Страница 412: ...10 18 MPC8240 Integrated Processor User s Manual Programming Guidelines ...
Страница 454: ...12 14 MPC8240 Integrated Processor User s Manual Internal Arbitration ...
Страница 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Страница 516: ...16 14 Watchpoint Trigger Applications ...
Страница 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
Страница 546: ...C 8 MPC8240 Integrated Processor User s Manual ...
Страница 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...