
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B
)
72
The PHB does not support byte merging or byte collapsing. Each and every single beat
transaction presented to the PPC Slave is presented to the PCI bus as a unique single beat
transfer.
2.3.2.4
PPC Master
The PPC Master can transfer data either in 1-to-8 byte single beat transactions or 32 byte, four
beat burst transactions. This limitation is strictly imposed by the PPC60x bus protocol. The PPC
Master attempts to move data using burst transfers whenever possible. If a transaction starts
on a non-cache line address, the PPC Master performs as many single beat transactions as
needed until the next highest cache line boundary is reached. If a write transaction ends on a
non-cache line boundary, then the PPC Master finishes the transaction with as many single
beat transactions as needed to complete the transaction.
The table shows the relationship between the starting addresses and the PPC60x bus
transaction types when write posting and read ahead are enabled.
Table 2-3 PPC Master Transaction Profiles and Starting Offsets
Start Offset
(i.e. from
0x00,0x20,0x40,etc.)
Write Profile
Read Profile
Notes
0x...00 -> 0x....07
Burst @ 0x00
Burst @ 0x20
....
Burst @ 0x00
Burst @ 0x20
....
Most efficient
0x....08 -> 0x....0f
Single @ 0x08
Single @ 0x10
Single @ 0x18
Burst @ 0x20
....
Burst @ 0x00
Burst @ 0x20
....
Discard read beat 0x00
0x....10 -> 0x....17
Single @ 0x10
Single @ 0x18
Burst @ 0x20
....
Burst @ 0x00
Burst @ 0x20
....
Discard read beat 0x00
and 0x08
0x....18 -> 0x....1f
Single @ 0x18
Burst @ 0x20
....
Single @ 0x18
Burst @ 0x20
....
Содержание MVME5100
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