Posted on May 17, 2011 at 13:34Hi-
You've identified a potential problem ''before'' causing yourself trouble - good for you.
As you sense - ''appropriating'' JTAG pins for other purposes will most always defeat the JTAG.
What to do? If your chip has a 2nd SPI port suggest that you develop your software on that port. (in this way you keep your JTAG functionality) After you're done/satisfied - carefully alter this code to the alternate function pins which are shared with JTAG. Doing this - you will lose JTAG.
One trick - very early in your code - ''before'' you change pins from their default JTAG - read a switch which - when active - will prevent the switch of the JTAG pins to alternate function (or GPIO). In this way - you can quickly/easily recover JTAG operation without resorting to more complex, time-consuming methods.
Hope this helps...
