muxed
-0 uart0_tx spi0_sclk
-1 uart0_rx spi0_mosi
-2 uart1_tx spi0_ss
-3 uart1_rx spi0_miso
+0 uart0_tx spi0_sclk uart2_tx uart3_tx
+1 uart0_rx spi0_mosi uart2_rx uart3_rx
+2 twi0_sda spi0_ss
+3 twi0_scl spi0_miso
+dedicated
+4 uart1_tx
+5 uart1_rx
+6 twi1_sda
+7 twi1_scl