20.2.4 ETAP EJTAG Boot
(ETAP_EJTAGBOOT) Command
The ETAP_EJTAGBOOT command causes the processor to fetch code from the
debug exception vector after a Reset. This allows the programmer to send instructions to
the processor to execute, instead of the processor fetching them from the normal Reset
vector. The Reset value of the EjtagBrk, ProbTrap and ProbE bits follows the setting of
the internal EJTAGBOOT indication.
If the EJTAGBOOT instruction has been given, and the internal EJTAGBOOT
indication is active, then the Reset value of the three bits is set
(‘1’), otherwise the Reset value is clear (‘0’).
The results of setting these bits are:
- Setting the EjtagBrk bit causes a
Debug interrupt exception to be requested right after the processor Reset from the
EJTAGBOOTinstruction - The debug handler is executed from the EJTAG memory because ProbTrap is set to indicate debug vector in EJTAG memory at 0xFF200200
- Service of the processor access is indicated because ProbEn is set
With this configuration in place, an interrupt exception will occur and the processor
fetches the handler from the DMSEG at 0xFF200200. Since ProbEn bit is
set, the processor will wait for the instruction to be provided by the probe.