10. Endian Mapping
187
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
10.4.3
PowerPC Little-endian Mode
In PowerPC little-endian mode, the PB Master swaps byte lanes according to
and munges
outgoing addresses PB_A[29:31] according to
. Address munging does not occur for burst and
extended cycles.
In PowerPC little-endian mode, the PB Master is restricted to transferring naturally aligned quantities.
External PCI masters or the PowerSpan II’s DMA channels can request transactions that are not
naturally aligned. The PB Master breaks up these requests into single byte transactions on the
processor bus, with a performance penalty.
The PB Slave asserts PB_TEA_ in response to a transaction that is not naturally aligned. These cases
are as follows:
•
PB_TSIZ = 3, 5, 6, 7 bytes
•
PB_TSIZ = 2 bytes and PB_A[31] = 1
For DMA transactions between the processor (60x) bus and the PCI-1 bus, the END bit in the
Transfer Control Register” on page 311
must be set to 11. For all other PowerPC little-endian transfers,
the END bit must be set to 01.
Seven
bytes
000
D0
D1
D2
D3
D4
D5
D6
D0
D1
D2
D3
D4
D5
D6
001
D1
D2
D3
D4
D5
D6
D7
D1
D2
D3
D4
D5
D6
D7
Double 000
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
Table 52: PowerSpan II Little-endian Mode Byte Lane Mapping
Transfer
Size
Start
Address
PowerPC Byte Lanes
PCI Byte Lanes
0
1
2
3
4
5
6
7
7
6
5
4
3
2
1
0