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Controlling UART RI Pin from u-boot

Question asked by Allen Kennedy on Apr 1, 2013
Latest reply on Apr 4, 2013 by Juan Antonio Gutierrez Rosas


  I have a iMX512 processor booting with u-boot.  I get to the prompt and it seems okay.  From here I added a command to u-boot so that I can toggle UART1s Ring Indicator Pin.  However I am unable to see the pin change state on a scope.

In my command function I:

- Disable Uart 1 (via UCR1 bit 0)


- Set IOMUXC_SW_PAD_CTL_PAD_KEY_COL4 to open drain (0x01ED) (1k pullup on output)

- Re-enable Uart1

- read RI state (via UCR3, bit 9)

- write a new RI state


I also print out the values of the registers before I modify them (except while the UART is disabled).


The UCR3 register indicates that the write was successful, as the new value is correct but the pin doesn't change state.

I know the peripheral is engaged and working and the clocking to it is correct because that's the terminal I use for u-boot.


Am I missing something? Do I need to get the IO mux controller to latch in the changes somehow?