UM0434 datasheet(375/390 Pages) STMICROELECTRONICS

375 / 390 page

Nexus3 module

UM0434

376/391

For example, if the

nex_mdo[n:0] port is 2 bits wide and the unique portion of an indirect

address TCODE is 5 bits, the remaining 1 bit of

nex_mdo[n:0] must be packed with a zero.

12.13

Auxiliary port arbitration

In a multiple Nexus environment, the Nexus3 module must arbitrate for the shared Nexus

port at the SoC level.The request scheme is implemented as a 2-bit request with various

levels of priority. The priority levels are defined in

Table 274 below. The Nexus3 module

receives a 1-bit grant signal (

npc_aux_grant) from the SoC level arbiter. When a grant is

received, the Nexus3 module begins transmitting its message following the protocol outlined

Chapter 12.11.2: Pin protocol on page 373.” The Nexus3 module maintains control of the

port, by asserting the

nex_aux_busy signal, until the MSEO state machine reaches the end

message state.

12.14

Examples

The following are examples of program trace and data trace messages.

Table 275 shows an example of an indirect branch message with 2 MDO/1 MSEO

configuration.

Table 276 shows the same example with an 8 MDO/2 MSEO configuration.

Note:

During clock 12, the nex_mdo[n:0] pins are ignored in the single MSEO case.

Table 274.

MDO request encodings

Request level

MDO request

Encoding(nex_aux_req[1:0])

Condition of queue

No request

No message to send

Low priority

Message queue less than half full

—10

Reserved

High priority

Message queue at least half full

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