UM0434 datasheet(331/390 Pages) STMICROELECTRONICS

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Nexus3 module

UM0434

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12.2

Enabling Nexus3 operation

The Nexus module is enabled by loading a single instruction, NEXUS3-Access

, into the

JTAG instruction register/OnCE OCMD register. For the e200z3 Nexus3 module, the OCMD

value is 0b00_0111_1100. Once enabled, the module is ready to accept control input

through the JTAG/OnCE pins.

The Nexus module is disabled when the JTAG state machine reaches the test-logic-reset

state. This state can be reached by the assertion of the

j_trst_b pin or by cycling through the

state machine using the

j_tms pin. The Nexus module can also be disabled if a power-on

reset (POR) event occurs. If the Nexus3 module is disabled, no trace output is provided, and

the module disables auxiliary port output pins,

nex_mdo[n:0], nex_mseo[1:0], and

nex_mcko. Nexus registers are not available for reads or writes.

Note:

See Nexus 3 Integration Guide for details on IEEE-ISTO 5001 compliance output pins &

multiple Nexus module configurations.

12.3

TCODEs supported

The Nexus3 pins allow for flexible transfer operations through public messages. A TCODE

defines the transfer format, the number and/or size of the packets to be transferred, and the

purpose of each packet. The

IEEE-ISTO 5001-2003 standard defines a set of public

messages. The Nexus3 block supports the public TCODEs seen in

Table 211. Each

message contains multiple packets transmitted in the order shown in the table.

Table 211.

Public TCODEs supported

Message name

Minimum

Packet

Size (Bits)

Maximum

Packet

Size (Bits)

Packet

type

Packet description

Debug status

Fixed

TCODE number = 0 (0x00)

Fixed

Source processor identifier (multiple Nexus

configuration)

Fixed

Debug status register (DS[31–24])

Ownership trace

message

Fixed

TCODE number = 2 (0x02)

Fixed

Source processor identifier (multiple Nexus

configuration)

Fixed

Task/process ID tag

Program trace–Direct

branch message

Fixed

TCODE number = 3 (0x03)

Fixed

Source processor identifier (multiple Nexus

configuration)

Variable

Number of sequential instructions executed since last

taken branch

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