How to Change the serial console

Summary

The serial console is essential for communication with and development of your design. This how-to guide will demonstrate the steps required to change the default serial debug console configuration.

Specifically, the phyBOARD-Zeta uses UART5 as the default serial console. This requires a breakout cable assembly to expose the RS-232 pins that are available on a pin header on the Zeta board, a null modem cable, and finally a serial cable to the host. The PEB-EVAL-02 board exposes UART1 via RS-232 on a DB9 connector. This will be the target configuration that the how-to guide will demonstrate.

Step-by-step guide

u-boot

To change the serial console for u-boot, you'll need to modify the CONFIG_CONS_INDEX and CONFIG_MXC_UART_BASE definitions in the u-boot source.

Change CONFIG_CONS_INDEX to indicate the index of the UART that is desired. In this case, we will change it from 5 to 1:

/* allow to overwrite serial and ethaddr */
#define CONFIG_ENV_OVERWRITE
#undef CONFIG_CONS_INDEX
#define CONFIG_CONS_INDEX 5
#define CONFIG_BAUDRATE 115200

/* allow to overwrite serial and ethaddr */
#define CONFIG_ENV_OVERWRITE
#undef CONFIG_CONS_INDEX
#define CONFIG_CONS_INDEX 1
#define CONFIG_BAUDRATE 115200

Change CONFIG_MXC_UART_BASE to indicate the UART base address of the UART that is desired. In this case, we will change it from 5 to 1:

#define CONFIG_MXC_UART_BASE        UART5_IPS_BASE_ADDR

#define CONFIG_MXC_UART_BASE        UART1_IPS_BASE_ADDR

Verify the desired UART pins are muxed correctly in u-boot:

&uart1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart1>;
	assigned-clocks = <&clks IMX7D_UART1_ROOT_SRC>;
	assigned-clock-parents = <&clks IMX7D_PLL_SYS_MAIN_240M_CLK>;
	status = "okay";
};

Linux

Change the SERIAL_CONSOLE to indicate the desired 'ttymxc' device in the imx7d_phyboard_zeta_001 machine configuration. In this case, we will change it from a 4 to a 0:

SERIAL_CONSOLE = "115200 ttymxc4"

SERIAL_CONSOLE = "115200 ttymxc0"

You'll also want to verify the desired UART pins are muxed in your device tree:

&uart1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart1>;
	assigned-clocks = <&clks IMX7D_UART1_ROOT_SRC>;
	assigned-clock-parents = <&clks IMX7D_PLL_SYS_MAIN_240M_CLK>;
	status = "okay";
};

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