(1) unifies the iomux definitions - previously some pins had them, and some didn't. This effectively made it impossible to use the pinmuxes without editing the header file in the standard distribution tree.
(2) unifies the pin definitions so that every pin now has a suffix. This makes it *much* easier to see when a pin is in use in your code, because it will always have a definition in your board.h file.
For anyone who is already using this CPU, a couple of small changes are needed to existing code;
In respect of (1) add IOMUX decorators to your pin definitions. You will find defaults in haardware/imxrt_iomux.h. Every pin should have a IOMUX decorator and in general the defaults should be OK. So while previously in your board.h file you might have had;
You will now have;
In respect of (2) you will need to add selectors for any function that previously only had one pinning option. There aren't many of those but LPUART1 is a good example. That just means adding into your board.h something like;
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