TMPR4956C datasheet(176/286 Pages) TOSHIBA

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Chapter 11 TX4956 System Interface

11-8

If data have not been returned to the issued processor read request, the applicable request is said

to be “on hold.” This state continues until the requested read data are returned.

The external agent must be able to accept processor read requests at any time if both of the

following two conditions are met.

•

There is no processor read request that is on hold.

•

The RdRdy* signal is asserted for 1 cycle 2 cycles before the issue cycle.

11.2.6.4 Processor write requests

When the processor issues a write request, the specified resources are accessed, then the data are

written to those resources.

Processor write requests are completed when the final data word is transferred to the external

agent.

The external agent must be able to accept processor write requests at any time if either of the two

following conditions are met.

•

There is no processor read request that is on hold.

•

The WrRdy* signal is asserted for 1 cycle 2 cycles before the issue cycle.

11.2.6.5 External requests

As illustrated in Figure 11.2.9, there are three types of external request: read, write, and null.

Figure 11.2.9 External Requests

Read requests are used to call 1-word data from processor internal resources. Write requests are

used to write 1-word data to the processor internal resources. Null requests are requests that do not

require processor operation.

As illustrated in Figure 11.2.10, the processor uses arbitration signals ExtRqst* and Release* to

control the flow of external requests. The external agent cannot issue external requests unless access

privileges to the system interface are obtained. In order to do so, the external agent asserts the

ExtRqst* signal, then waits until the processor asserts the Release* signal for 1 cycle.

External request

• Read

• Write

• Null

TX4956

External agent

TMPR4956C Datasheet(PDF) 176 Page - Toshiba Semiconductor