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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
127
Intel XScale
®
Processor—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
DBG.HLD_RST can only be cleared by scanning in a ‘0’ to DBG_SR[1] and scanning in
the appropriate values for the DCSR and DBG.BRK.
3.6.11.2.2
DBG.BRK
DBG.BRK allows the debugger to generate an external debug break and
asynchronously re-direct execution to a debug handling routine.
A debugger sets an external debug break by scanning data into the DBG_SR with
DBG_SR[2] set and the desired value to set the DCSR JTAG writable bits in
DBG_SR[34:3].
Once an external debug break is set, it remains set internally until a debug exception
occurs. In Monitor mode, external debug breaks detected during abort mode are
pended until the processor exits abort mode. In Halt mode, breaks detected during
SDS are pended until the processor exits SDS. When an external debug break is
detected outside of these two cases, the processor ceases executing instructions as
quickly as possible. This minimizes breakpoint skid, by reducing the number of
instructions that can execute after the external debug break is requested. However, the
processor will continue to process any instructions which may have already begun
execution. Debug mode will not be entered until all processor activity has ceased in an
orderly fashion.
3.6.11.2.3
DBG.DCSR
The DCSR is updated with the value loaded into DBG.DCSR following an Update_DR.
Only bits specified as writable by JTAG in
3.6.11.3
DBGTX JTAG Command
The ‘DBGTX’ JTAG instruction selects the DBGTX JTAG data register. The JTAG op code
for this instruction is ‘0b10000’. Once the DBGTX data register is selected, the
debugger can receive data from the debug handler.
3.6.11.4
DBGTX JTAG Register
The DBGTX JTAG instruction selects the Debug JTAG Data register (
debugger uses the DBGTX data register to poll for breaks (internal and external) to
debug mode and once in debug mode, to read data from the debug handler.