Lpc2000

My suggestion:

On low pin count devices, should you ever revisit the concept of a
"secondary JTAG port," reserve a pin that selects the JTAG port at
reset.  Alternatively, make the port with the ETM module the secondary
port, since this is the one that's more difficult to fit into most
designs.  Enabling (what usually amounts to) the main JTAG interface in
software is too fragile for such a debug mechanism.

I realize that subtle debug improvements are hard to sell.  But the
usefulness of the 210X JTAG is really diminished by the way it is
implemented, in my opinion.