+@anchor{usingopenocdsmpwithgdb}
+@section Using OpenOCD SMP with GDB
+@cindex SMP
+@cindex RTOS
+@cindex hwthread
+OpenOCD includes a pseudo RTOS called @emph{hwthread} that presents CPU cores
+("hardware threads") in an SMP system as threads to GDB. With this extension,
+GDB can be used to inspect the state of an SMP system in a natural way.
+After halting the system, using the GDB command @command{info threads} will
+list the context of each active CPU core in the system. GDB's @command{thread}
+command can be used to switch the view to a different CPU core.
+The @command{step} and @command{stepi} commands can be used to step a specific core
+while other cores are free-running or remain halted, depending on the
+scheduler-locking mode configured in GDB.
+
+@section Legacy SMP core switching support
+@quotation Note
+This method is deprecated in favor of the @emph{hwthread} pseudo RTOS.
+@end quotation
+
+For SMP support following GDB serial protocol packet have been defined :
+@itemize @bullet
+@item j - smp status request
+@item J - smp set request
+@end itemize
+
+OpenOCD implements :
+@itemize @bullet
+@item @option{jc} packet for reading core id displayed by
+GDB connection. Reply is @option{XXXXXXXX} (8 hex digits giving core id) or
+ @option{E01} for target not smp.
+@item @option{JcXXXXXXXX} (8 hex digits) packet for setting core id displayed at next GDB continue
+(core id -1 is reserved for returning to normal resume mode). Reply @option{E01}
+for target not smp or @option{OK} on success.
+@end itemize
+
+Handling of this packet within GDB can be done :
+@itemize @bullet
+@item by the creation of an internal variable (i.e @option{_core}) by mean
+of function allocate_computed_value allowing following GDB command.
+@example
+set $_core 1
+#Jc01 packet is sent
+print $_core
+#jc packet is sent and result is affected in $
+@end example
+
+@item by the usage of GDB maintenance command as described in following example (2 cpus in SMP with
+core id 0 and 1 @pxref{definecputargetsworkinginsmp,,Define CPU targets working in SMP}).
+
+@example
+# toggle0 : force display of coreid 0
+define toggle0
+maint packet Jc0
+continue
+main packet Jc-1
+end
+# toggle1 : force display of coreid 1
+define toggle1
+maint packet Jc1
+continue
+main packet Jc-1
+end
+@end example
+@end itemize
+