8.9.3. TRACECTL and TRACEDATA multiplexing

If pin minimization is a priority, and it is also necessary to support legacy TPAs that still require TRACECTL, it is possible to support both systems in the same implementation by multiplexing the TRACECTL pin with a data pin. This enables the support of the current method of using the control pin at the same time as enabling the connection of a next generation trace capture device with the added advantage of an extra data pin. A possible choice for this extra data pin would be the most significant bit because this could be switched without having to change the signal paths of any other connection.

The ability to switch TRACECTL with a data pin is not directly supported by the TPIU. Problems can arise when trying to drive multiple connector pins, for connector re-use, because of impedance and load differences. In addition, timing can be affected because of the inclusion of a multiplexor on a limited number of signals

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