Debug Support
e200z3 Power Architecture Core Reference Manual, Rev. 2
9-14
Freescale Semiconductor
The initial entry by the CPU into the debug state (or mode) from normal, stopped, halted, or checkstop
states (all indicated by the OnCE status register (OSR) described in
Section 9.5.5.1, “OnCE Status Register
) by assertion of one or more debug requests begins a debug session. The jd_debug_b output signal
indicates that a debug session is in progress, and the OSR indicates that the CPU is in the debug state.
Instructions may be single-stepped by scanning new values into the CPUSCR and performing a OnCE
Go+NoExit command (see
Section 9.5.5.2, “OnCE Command Register (OCMD)”
). The CPU then
temporarily exits the debug state (but not the debug session) to execute the instruction and returns to the
debug state (again indicated by the OSR). The debug session remains in force until the final Go+Exit
command is executed, at which time the CPU returns to its previous state (unless a new debug request is
pending). A scan into the CPUSCR is required before executing each Go+Exit or Go+NoExit command.
9.5.2
JTAG/OnCE Signals
The JTAG/OnCE interface is used to transfer OnCE instructions and data to the OnCE control block.
Depending on the resource being accessed, the CPU may need to be placed in debug mode. For resources
outside the CPU block and contained in the OnCE block, the processor is not disturbed and may continue
execution. If a processor resource is required, an internal debug request (dbg_dbgrq) may be asserted to
the CPU by the OnCE controller, and causes the CPU to finish the instruction being executed, save the
instruction pipeline information, enter debug mode, and wait for further commands. Asserting dbg_dbgrq
causes the chip to exit the low-power mode enabled by setting MSR[WE].
details the primary JTAG/OnCE interface signals.
A full description of JTAG signals is provided in
Section 7.3.2, “JTAG ID Signals.”
Table 9-3. JTAG/OnCE Primary Interface Signals
Signal Name
I/O
Description
j_trst_b
I
JTAG test reset
j_tclk
I
JTAG test clock
j_tms
I
JTAG test mode select
j_tdi
I
JTAG test data input
j_tdo
O
Test data out to master controller or pad
j_tdo_en
O
Enables TDO output buffer
Set when the TAP controller is in the Shift-DR
or Shift-IR state.