Download Open On-Chip Debugger: OpenOCD User's Guide

Chapter 9: Reset Configuration
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[Command]
This validates the scan chain using just the four standard JTAG signals (TMS, TCK,
TDI, TDO). It starts by issuing a JTAG-only reset. Then it performs checks to verify
that the scan chain configuration matches the TAPs it can observe. Those checks
include checking IDCODE values for each active TAP, and verifying the length of
their instruction registers using TAP -ircapture and -irmask values. If these tests
all pass, TAP setup events are issued to all TAPs with handlers for that event.
jtag arp_init
[Command]
This uses TRST and SRST to try resetting everything on the JTAG scan chain (and
anything else connected to SRST). It then invokes the logic of jtag arp_init.
jtag arp_init-reset