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Debug Support
e200z3 Power Architecture Core Reference Manual, Rev. 2
Freescale Semiconductor
9-11
the CPU is halted at a recoverable boundary, and an external debug control module may control CPU
operation through the OnCE logic. No debug interrupts can occur while DBCR0[EDM] remains set.
NOTE
On the initial setting of DBCR0[EDM], other bits in DBCR0 are unchanged.
After DBCR0[EDM] is set, all debug register resources may be
subsequently controlled through the OnCE interface. DBSR should be
cleared as part of the process of enabling external debug activity. The CPU
should be placed into debug mode through the OCR[DR] control bit before
setting EDM. This allows the debugger to cleanly write to the DBCRn
registers and the DBSR to clear out any residual state/control information
that could cause unintended operation.
NOTE
It is intended for the CPU to remain in external debug mode
(DBCR0[EDM] = 1) in order to single-step or perform other debug mode
entry/reentry through the OCR[DR], by performing OnCE Go+NoExit
commands, or by assertion of jd_de_b.
NOTE
DBCR0[EDM] operation is blocked if the OnCE operation is disabled
(jd_en_once negated) regardless of whether it is set or cleared. This means
that if DBCR0[EDM] was previously set and then jd_en_once is negated
(this should not occur), entry into debug mode is blocked, all events are
blocked, and watchpoints are blocked.
Due to clock domain design, the CPU clock (m_clk) must be active for writes to be performed to debug
registers other than the OnCE command register (OCMD), the OnCE control register (OCR), or
DBCR0[EDM]. Register read data is synchronized back to the j_tclk clock domain. The OnCE control
register provides the capability of signaling the system level clock controller that the CPU clock should be
activated if not already active.
Updates to DBCRn, DBSR, and DBCNT through the OnCE interface should be performed with the CPU
in debug mode to guarantee proper operation. Due to the various points in the CPU pipeline where control
is sampled and event handshaking is performed, it is possible that modifications to these registers while
the CPU is running may result in early or late entry into debug mode and incorrect status information
posted in DBSR.
9.5.1
OnCE Introduction
The on-chip emulation circuitry (OnCE/Nexus class 1 interface) provides a means of interacting with the
core and integrated system so that a user may examine registers, memory, or on-chip peripherals. OnCE
operation is controlled through an industry-standard IEEE 1149.1 TAP controller. By using JTAG
instructions, the external hardware debugger can freeze or halt the CPU, read and write internal state, and
resume normal execution. The core does not contain IEEE 1149.1 standard boundary cells on its interface,
as it is a building block for further integration. It does not support the JTAG-related boundary scan
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