check mux mode when using digitalWrite

[bigdinotech]

-check and make sure that the pin is in GPIO_MUX_MODE when doing a
digitalWrite()
-this has a slight performance impact of digitalWrite
-it also comsumes an extra byte in SRAM per pin
-it does however give us the ability to track the muxing state of each
pin

[bigdinotech]

@SidLeung @eriknyquist please review
@khanning @agdl @facchinm this should fix #280 and #334
as I mentioned before there is a slight performance impact but it seems more negligeable than I initially though

[eriknyquist]

I think I2S, I2SDMA and possibly some more need to set pinMuxMode too. See the following two commits, where I removed them, for reference;

3d3c1f9
1a5e3f7

[agdl]

Works for me!

[noelpaz]

@russmcinnis . Can you please verify?

[bigdinotech]

@eriknyquist I2S will be added once the @SidLeung finishes the changes for it

[russmcinnis]

I test variations of the examples and it works for me too. I was doing some testing using sketch delayMicroseconds() to just measure the frequency of 100 consecutive digitalRead() or digitalWrite() calls without checking any signals. The digitalWrite() function speed with the mux checking added was about 75% of the speed without it.

[bigdinotech]

@russmcinnis please test this with CurieSoftwareSerial library.
It should only affect the tx performance of it and the appropriate changes is already in this commit

[eriknyquist]

@russmcinnis can you see what SoftwareSerial behaviour is like with these changes?

[russmcinnis]

I don't see any difference. I ran the BAT test that hooks up SoftwareSerial pins to Hardware Serial (Serial1) pins. The test runs a lot of transactions and passes.

Next I ran most of the baud rates by looping:
mySerial.write(0x1);
I have some tables of the frequency from the scope and I don't see any difference. I thought I would see a difference since before I was measuring digitalWrite(HIGH and LOW) in a tight loop and saw performance fall by 25%.

[bigdinotech]

@calvinatintel please merge this one also. Jenkins merger is also failing for this one