19.6.6 JTAG/SWD PORT BEHAVIOR

Once the debugger is attached, the DSU takes ownership of the JTAG port pins to prevent application code from reclaiming them. If the debugger switches to SWD mode using the Arm JTAG to SWD switching sequence, the unused JTAG I/Os are released, claiming the SWCLK and SWDIO I/Os only. Once in SWD mode, the debugger can switch back to JTAG mode using the Arm SWD to JTAG switching sequence at which point the hardware will claim all the JTAG I/Os again.

Note: Releasing and reclaiming of JTAG ports are handled outside of the DSU and the DSU is unaware of this operation.