TMPR4956C datasheet(191/286 Pages) TOSHIBA

191 / 286 page

Chapter 11 TX4956 System Interface

11-23

11.2.8.11 Read response protocol

The external agent must use the read response protocol to return data to the processor if a

processor read request has been received. The sequence of the read response protocol is as follows.

The external agent waits for the processor to automatically execute a shift into the slave state.

The external agent uses either a single data cycle or a series of data cycles to return data.

After issuing the final data cycle, the read response ends, then the external agent sets the

SysCmd and SysAD busses to tri-state.

The system interface returns to the master state.

Note:

After issuing a read response, the processor automatically shifts to the slave state.

Data identifiers of a data cycle must indicate that the data are response data.

Final data cycle identifiers must contain an indication that a cycle is the final data cycle.

In the case of read responses to non-coherent block read requests, it is not necessary for the

response data to check the initial cache state. The cache state is automatically set to exclusively

dirty.

Data identifiers of data cycles can send notification of transfer data errors in those cycles. The

external agent must return data blocks with the correct size even when there is an error in the

data. Whether there is a single error or multiple errors in the read response data cycles, the

processor processes them as bus errors.

Read responses must always be returned to the processor when a processor read request is being

held. Processor operation is not defined if a read response was returned in a state where there were

no processor read requests on hold.

Figure 11.2.22 illustrates a processor word read request and the subsequent word read response.

Also, Figure 11.2.23 illustrates the read response to a processor block read request when the system

interface is in the slave state.

TMPR4956C Datasheet(PDF) 191 Page - Toshiba Semiconductor