UM0434 datasheet(347/390 Pages) STMICROELECTRONICS

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Nexus3 module

UM0434

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12.5

Nexus3 register access through JTAG/OnCE

Access to Nexus3 register resources is enabled by loading a single instruction, NEXUS3-

Access, into the JTAG instruction register/OnCE OCMD register. For the Nexus3 block, the

OCMD value is 0b00_0111_1100.

Once the NEXUS3-Access instruction has been loaded, the JTAG/OnCE port allows

tool/target communications with all Nexus3 registers according to the register map in

Table 216.

Reading/writing of a Nexus3 register then requires two passes through the data-scan path

of the JTAG state machine 12 (see

Chapter 12.15: IEEE 1149.1 (JTAG) RD/WR sequences

on page 379”).

The first pass through the DR selects the Nexus3 register to be accessed by providing

an index (see

Table 216), and the direction, read/write. This is achieved by loading an

8-bit value into the JTAG data register (DR). This register has the format shown in

Table 241.

The second pass through the DR then shifts the data in or out of the JTAG port, least

significant bit first.

During a read access, data is latched from the selected Nexus register when the

JTAG state machine passes through the capture-DR state.

During a write access, data is latched into the selected Nexus register when the

JTAG state machine passes through the update-DR state.

12.6

Ownership trace

This section details the ownership trace features of the Nexus3 module.

12.6.1

Overview

Ownership trace provides a macroscopic view, such as task flow reconstruction, when

debugging software is written in a high-level or object-oriented language. It offers the

highest level of abstraction for tracking operating system software execution. This is

especially useful when the developer is not interested in debugging at lower levels.

Table 241.

Nexus3 Register Access through JTAG/OnCE (Example)

(7 bits)

(1 bit)

Nexus Register Index

R/W

Reset Value: 0x00

Table 242.

Nexus register example

Field

Description

Nexus Register Index

Selected from values in

Table 216

Read/write (R/W)

0 Read

1 Write

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