[FAQ] TDA4VM: How to test serial UART ports on board?

On J721e/J7200 main_uart0 is used as console. So there are other UART instances like main_uart1 that are brought out on the common processor board
via the micro USB port.

By default the pin mux is not set. So we need to set the right pin mux for the main_uart1 pins as below:

diff --git a/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts b/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
index 368e9f06a..913225010 100644
--- a/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
+++ b/arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts
@@ -168,6 +168,15 @@
                >;
        };
 
+       main_uart1_pins_default: main-uart1-pins-default {
+               pinctrl-single,pins = <
+                       J721E_IOPAD(0xc8, PIN_INPUT, 1) /* (U3) ECAP0_IN_APWM_OUT.I2C1_SCL */
+                       J721E_IOPAD(0xcc, PIN_OUTPUT, 1) /* (T3) EXT_REFCLK1.I2C1_SDA */
+                       J721E_IOPAD(0xb8, PIN_INPUT, 0) /* (U3) ECAP0_IN_APWM_OUT.I2C1_SCL */
+                       J721E_IOPAD(0xbc, PIN_OUTPUT, 0) /* (T3) EXT_REFCLK1.I2C1_SDA */
+               >;
+       };
+
        main_mmc1_pins_default: main-mmc1-pins-default {
                pinctrl-single,pins = <
                        J721E_IOPAD(0x104, PIN_INPUT, 0) /* (M20) MMC1_CMD */
@@ -265,6 +274,12 @@
        pinctrl-0 = <&mcu_cpsw_pins_default &mcu_mdio_pins_default>;
 };
 
+&main_uart1 {
+       pinctrl-names = "default";
+       pinctrl-0 = <&main_uart1_pins_default>;
+       status = "okay";
+};
+

The above is for main_uart1 instance on the j7200 EVM as an example.

The sysconfig pins can be looked up for each instance using the sysconfig tool: https://dev.ti.com/sysconfig/#/start

Customers using custom board will need to map the corresponding pins that are mapped to main_uart1.
The above patch takes care of the hardware setup.

Target side steps:

Boot to Linux command prompt & on the J7200 terminal, execute the below commands:

stty -F /dev/ttyS3 115200 -crtscts

cat /dev/ttyS3

The above will prepare the j7200 for an RX on the main_uart1.

Host side steps:

i.e Linux machine connected to EVM's UART micro USB port.

The /dev/ttyUSB1 maps to the main_uart1. Hence below commands:

stty -F /dev/ttyUSB1 115200 -crtscts
echo hello > /dev/ttyUSB1

The above commands will transfer 'hello' from Host TX to J7200 MAIN_UART1 RX and one should see that on the J7200 console.
Similar approach can be followed for other instances that are available on board.

Regards,
Keerthy