Store Operations; Load Operations - IBM PowerPC 604 User Manual

8.6.1.1 Store Operations
There are
three
operations defined for direct-store store operations from the 604 to the
BUC, defined as follows:
1. Store immediate operations transfer up to 32 bits of data each from the 604 to the
BUC.
2. Store last operations transfer up to 32 bits of data each from the 604 to the BUC.
3. Store reply from the BUC reveals the success/failure of that direct-store access to
the 604.
A direct-store store access consists of one or more data transfer operations followed by the
1/0 store reply operation from the BUC. If the data can
be
transferred in one 32-bit data
transaction, it is marked as a store last operation followed by the store reply operation; no
store immediate operation is involved in the transfer, as shown in the following sequence:
STORE LAST (from 604)
•
•
STORE REPLY (from BUC)
However, if more data is involved in the direct-store access, there will be one or more store
immediate operations. The BUC can detect when the last data is being transferred by
looking for the store last opcode, as shown in the following sequence:
STORE IMMEDIATE(s)
•
•
STORE LAST
•
•
STORE REPLY
8.6.1.2 Load Operations
Direct-store load accesses are similar to store operations, except that the 604 latches data
from the addressed BUC rather
than
supplying the data to the BUC. As with memory
accesses, the 604 is the master on both load and store operations; the external system must
provide the data bus grant to the 604 when the BUC is ready to supply the data to the 604.
Chapter 8.
System
Interface Operation
8-41