Chapter 36 Nexus Development Interface (NDI)
MPC5602P Microcontroller Reference Manual, Rev. 4
908
Freescale Semiconductor
36.12.3.2 CPU Debug Acknowledge (cpu_dbgack)
The
cpu_dbgack
signal is asserted by the CPU upon entering the debug state. This signal is used as part
of the handshake mechanism between the OnCE control logic and the rest of the CPU. The CPU core may
enter debug mode either through a software or hardware event.
36.12.3.3 CPU Address, Attributes
The CPU address and attribute information are used by a Nexus class 2-4 debug unit with information for
real-time address trace information.
36.12.3.4 CPU Data
The CPU data bus(es) are used to supply a Nexus class 2-4 debug unit with information for real-time data
trace capability.
36.12.4 OnCE Interface Signals
The following paragraphs describe additional OnCE interface signals to other external blocks such as a
Nexus Controller and external blocks which may need information pertaining to debug operation.
36.12.4.1 OnCE Enable (jd_en_once)
The OnCE enable signal
jd_en_once
is used to enable the OnCE controller to allow certain instructions
and operations to be executed. Assertion of this signal will enable the full OnCE command set, as well as
operation of control signals and OnCE Control register functions. When this signal is disabled, only the
Bypass, ID and Enable_OnCE commands are executed by the OnCE unit, and all other commands default
to a “Bypass” command. The OnCE Status register (OSR) is not visible when OnCE operation is disabled.
In addition, OnCE Control register (OCR) functions are disabled, as is the operation of the
jd_de_b
input.
Secure systems may choose to leave the
jd_en_once
signal negated until a security check has been
performed. Other systems should tie this signal asserted to enable full OnCE operation. The
j_en_once_regsel
output signal is provided to assist external logic performing security checks.
The
jd_en_once
input must only change state during the Test-Logic-Reset, Run-Test/Idle, or Update_DR
TAP states. A new value will take affect after one additional
j_tclk
cycle of synchronization. In addition,
jd_enable_once
input signal must not change state during a debug session, or undefined activity may
occur.
36.12.4.2 OnCE Debug Request/Event (jd_de_b, jd_de_en)
If implemented at the SoC level, a system level bidirectional open drain debug event pin
DE_b
(not part
of the interface) provides a fast means of entering the Debug Mode of operation from an external command
controller (when input) as well as a fast means of acknowledging the entering of the Debug Mode of
operation to an external command controller (when output). The assertion of this pin by a command
controller causes the CPU core to finish the current instruction being executed, save the instruction
pipeline information, enter Debug Mode, and wait for commands to be entered. If
DE_b
was used to enter
the Debug Mode then
DE_b
must be negated after the OnCE controller responds with an acknowledge and