One of the most difficult things to deal with is port set up on recent powerful CPU's.

Chip makers are trying to accommodate as wide a range of hardware  applications as
possible. Consequently even though a chip may have 100 pins each of those pins may
have different functions. Input, output, capture, oscillator in, frequency out,
analog input, PWM out and so on and so on.

This is a nightmare for the hardware application engineers. Get it wrong and your
hardware won't work.

Switch registers are provided to set up the ports. There could be hundreds of switch
registers.  Here is a list for the ARM. Two switch registers in series give four
combinations. Some of the combinations may not make sense and become not allowed or
do nothing. See my attached illustration.

Three switches in series gives nine combinations! A real nightmare indeed.

With every drawback there is a business opportunity. Somebody could set up a port
configuration service where you can mail them a chip and they can set it up for your
needs and mail it back. The switch registers being in flash memory don't forget.
Something you could do in your home. Also possible is a program that generates the
ASCii source code that sets up the ports. You tell it what you want the pin to do. A
program that writes a program.

Paul Lamar

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