PXN20RM Datasheet, PDF (1193/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Nexus Development Interface (NDI)
Reading/writing of a Nexus3+ register then requires two (2) passes through the data-scan (DR) path of the
JTAG state machine (see 36.6.10.8).
1. The first pass through the DR selects the Nexus3+ register to be accessed by providing an index
(see Table 36-19), and the direction (read/write). This is achieved by loading an 8-bit value into the
JTAG data register (DR). This register has the following format:
(7 bits)
(1 bit)
Nexus Register Index
R/W
RESET Value: 0x00
Nexus Register Index:
Read/Write (R/W)
Selected from values in Table 36-19
0 Read
1 Write
2. The second pass through the DR then shifts the data in or out of the JTAG port, LSB first.
a) During a read access, data is latched from the selected Nexus register when the JTAG state
machine passes through the CAPTURE-DR state.
b) During a write access, data is latched into the selected Nexus register when the JTAG state
machine passes through the UPDATE-DR state.
36.6.10 Nexus3+ Functional Description
36.6.10.1 Debug Status Messages
Debug Status Messages report low power mode and debug status. Debug Status Messages are enabled
when Nexus 3+ is enabled. Entering/exiting Debug Mode as well as entering a Low Power Mode triggers
a Debug Status Message, indicating the value of the most significant byte in the Development Status
register. Debug status information is sent out in the following format:
Table 36-30. Debug Status Message Format
(8 bits)
DS[31:24]
Fixed Length = 18 bits
(4 bits)
(6 bits)
Source Processor TCODE (000000)
36.6.10.2 Ownership Trace
This section details the ownership trace features of the Nexus3+ module.
36.6.10.2.1 Overview
Ownership trace provides a macroscopic view, such as task flow reconstruction, when debugging software
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.
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
36-43