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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Reference Number: 306262-004US
67
Functional Overview—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
2.2.12
Debug Unit
The debug unit is accessed through the JTAG port. The industry-standard, IEEE 1149.1
JTAG port consists of a test access port (TAP) controller, boundary-scan register,
instruction and data registers, and dedicated signals JTG_TMS, JTG_TDI, JTG_TDO,
JTG_TCK, and JTG_TRST_N.
The debug unit — when used with debugger application code running on a host system
outside of the Intel XScale processor — allows a program, running on the Intel XScale
processor, to be debugged. It allows the debugger application code or a debug
exception to stop program execution and redirect execution to a debug-handling
routine.
Debug exceptions are instruction breakpoint, data breakpoint, software breakpoint,
external debug breakpoint, exception vector trap, and trace buffer full breakpoint. Once
execution has stopped, the debugger application code can examine or modify the Intel
XScale processor’s state, coprocessor state, or memory. The debugger application code
can then restart program execution.
The debug unit has two hardware-instruction, break point registers; two hardware,
data-breakpoint registers; and a hardware, data-breakpoint control register. The
second data-breakpoint register can be alternatively used as a mask register for the
first data-breakpoint register.
A 256-entry trace buffer provides the ability to capture control flow messages or
addresses. A JTAG instruction (LDIC) can be used to download a debug handler via the
JTAG port to the mini-instruction cache (the I-cache has a 2-Kbyte, mini-instruction
cache, like the mini-data cache, that is used only to hold a debug handler).