
Chapter 7. Direct-Store Interface
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7.3 Store Operations
Store operations are defined for the 60x as follows:
Store immediate and store last operations transfer up to 32 bits of data to the device.
A store reply from the slave device indicates the success or failure of that access.
A direct-store access consists of one or more data transfer operations followed by a store
reply operation from the slave device. 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, shown in the following:
STORE LAST (from 60x).....STORE REPLY (from slave device)
If more data is involved, there is one or more store immediate operations. The slave device
detects the last transfer by looking for the store last transfer code, shown in the following:
STORE IMMEDIATE(s).....STORE LAST....STORE REPLY
7.4 Load Operations
Direct-store load accesses are like stores, except that the 60x receives instead of transmits
data. As with basic transfer protocol, the 60x is master on both load and store operations.
The system must grant the data bus to the 60x when the device is ready to provide data.
Direct-store load requests have no analogous store operation; these address-only operations
inform the addressed device of the number of bytes required on the subsequent load
immediate/load last operations. The simplest, 32-bit or less, direct-store load is as follows:
LOAD REQUEST.....LOAD LAST.....LOAD REPLY (from slave device)
If more data is involved, there is one or more load immediate operations. The device detects
the last data transfer by looking for the load last transfer code, shown in the following:
LOAD REQUEST.....LOAD IMMEDIATE(s).....LOAD LAST.....LOAD REPLY
Three of the seven defined operations are address-only transactions, which like basic
transfer protocol, do not use the data bus. Unlike the basic transfer protocol, however, these
transactions are not broadcast from one master to all snooping devices; rather, they pass
control information between the processor and a specific slave device.