Background: In JTAG boot mode, the user can select independent JTAG mode to support a debugger connected to the ARM DAP controller and another tool connected to the Xilinx PL TAP controller.
The Xilinx PL TAP controller is accessible using the PL JTAG interface connected to dedicated PL pins. The access to the ARM DAP controller (for another tool) is done using the EMIO JTAG interface. This requires the user to download a bitstream into the PL. The bitstream can be downloaded using the Xilinx PL TAP controller.
The Issue: In early Zynq revisions, this functionality does not exist and independent JTAG is not possible in JTAG boot mode. In those cases, if independent JTAG is selected the PL TAP controller is accessible but the PS cannot be accessed through the DAP and will remain perpetually in an idle state.