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]
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 ...