Initializing UART1 after raw boot from SD-Card - iMX.6

[adrianthewlis]

I am working on low-level boot code. The first thing I need to do is get some debug out of UART1. So far I can't get a signal out.

Tx line is CSI0_DATA10, Rx line is CSI0_DATA11... although at this point I am not interested in input. I am sure I have the right pins, as I ran a test with it switched to GPIO mode.

For both lines MUX is set to Alt3, and PAD_CTL to 0x0001b0b0, the UART1_RX daisy chain is set to 0 (although I tried all four values).

I am monitoring the TRDY in USR1 and writing bytes to UTXD when its set. By toggling an LED after an appropriate number of writes, I can tell that the UART module is working fine and set to the right baud rate.

Other than the MUX, CTL and daisy chain regs, is there anything else that controls/inhibits signals from the UART pins?

[igorpadykov]

Hi Adrian

it is recommended to check that uart clocks are enabled in CCM_CCGRn registers, then

one can try to run OS-less UART1 test code with SDK (one can run it with jtag),

recommended to check signals with oscilloscope

i.MX 6Series Platform SDK  : Bare-metal SDK for the i.MX 6

then compare SDK register settings with uboot/linux.

Best regards

igor

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