The 14 Pin Port J2205 on Series 3 (BCM7401 based) and Series 4 (BCM7413) is the EJTAG Port.

PIN 1 - TRST_N
PIN 3 - TDI
PIN 5 - TDO
PIN 7 - TMS
PIN 9 - TCK
PIN 11 -
PIN 13 - N/C

PIN 2 - GND
PIN 4 - GND
PIN 6 - GND
PIN 8 - GND
PIN 10 - GND
PIN 12 - N/C
PIN 14 - VCC

Square pad is PIN 1. on Series 4 the JTAG port is in the cable card slot
VCC is 3.3V so you need 3.3V compatible JTAG Adapter.

Also R2201 (4.7K) must be tied to GND to enable JTAG.

Hope this helps, if there are enough interest I can work on the JTAG and post results here.