AM2634-Q1: Pinmux Setting Problems For SPI CS pin

Dear Expert

As title description, for example

AM2634 SPI4 support two CS, (A14) & (M1) for CS0, (K2) for CS1

So I except I can create these two pin assignment in MCSPI PIN Configuration,

Create CS0 is fine without error

But create CS1 error happens, !!

My question is

1. Why I can not choice pin "K2" for CS1?

2. Why MCAN0_RX/M1 appear on pinmux tool for CS1? Not pin K1?

Or, May I miss something?

Many Thanks

Gibbs