AM3351: Unable to Enable UART in Buildroot Linux Kernel

Ayla Shiva

Part Number: AM3351

Hi,

I'm working on a Customized Linux Kernel bringup whch uses 4.14.71 Kernel, on BBB Rev C,BBB Board was able to Bringup, I have an Application which uses UART to communicate with Some Serial Devices,unfortunately i could not able to Enable UART in this setup, I have tried multiple ways/Approaches, but of no help, I have tried to Edit uEnv.txt and enableld BB-UARTx, but of no-help, Any suggestions/work-aroound for this Problem.

Thanks,

Shiva.

over 4 years ago

0 Bin Liu over 4 years ago

TI__Guru**** 175641 points

Hi Shiva,

It seems to me that you are able to build kernel v4.14.71 and run it on BBB rev C, but you need to enable another UART port for your application. Is my understanding correct? If so which UART port you want to enable?

0 Ayla Shiva over 4 years ago

Intellectual 680 points

Hi Bin Liu,

Yes, your understanding about my application is exactly right, I want to enable UART 1 which are pinmuxed on p9.24 and P9.26.

Thanks.

Shiva

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Hi Shiva,

You would have to modify the BBB device tree file to set the pinmux and enable the UART port. Following is an example.

diff --git a/arch/arm/boot/dts/am335x-boneblack.dts b/arch/arm/boot/dts/am335x-boneblack.dts
index 83c55cb7f3f0..14e65a83f286 100644
--- a/arch/arm/boot/dts/am335x-boneblack.dts
+++ b/arch/arm/boot/dts/am335x-boneblack.dts
@@ -32,6 +32,12 @@ oppnitro-1000000000 {
 };
 
 &am33xx_pinmux {
+       uart1_pins: uart1_pins {
+               pinctrl-single,pins = <
+                       AM33XX_IOPAD(0x980, PIN_INPUT_PULLUP | MUX_MODE0)       /* uart1_rxd.uart1_rxd */
+                       AM33XX_IOPAD(0x984, PIN_OUTPUT_PULLDOWN | MUX_MODE0)    /* uart1_txd.uart1_txd */
+               >;
+       };
 
        uart4_pins: uart4_pins {
                pinctrl-single,pins = <
@@ -43,6 +49,12 @@ AM33XX_IOPAD(0x874, PIN_OUTPUT_PULLDOWN | MUX_MODE6) /* gpmc_wpn.uart4_txd,    P
        };
 };
 
+&uart1 {
+       pinctrl-names = "default";
+       pinctrl-0 = <&uart1_pins>;
+       status = "okay";
+};
+
 &uart4 {
        pinctrl-names = "default";
        pinctrl-0 = <&uart4_pins>;

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Hi Bin,

I have Added the above Mentioned Code for UART1 in am335x-boneblack.dts file and generated the dtb file, I have copied this dtb file and booted the BBB, BBB booted, after boot-up when i issue the ls /dev/ command I cant see any device with ttyO*.

Is there any thing I need to do after this step, Like enabling the Pin for UART functionality using config?

Thanks,

Shiva.

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Hi Shiva,

What is the output of you run the following command after Linux is booted?

# dmesg | grep tty

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Hi Bin,

Below is the response of the grep | tty command

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Please run the following command and provide its output.

# cat /sys/firmware/devicetree/base/ocp/serial@48022000/status

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Hi Bin,

This is the response I could see.

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Hi Shiva,

As you see in the output, UART1 is disabled in device tree. So either you didn't patch the kernel correctly, or you didn't use the patched dtb file to boot Linux.

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Hi Bin,

Now I could see the Change as Okay in

# cat /sys/firmware/devicetree/base/ocp/serial@48022000/status

But I could not see the ttyO in /dev.

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

It should be /dev/ttyS1. Run command 'dmesg | grep tty', then you should see the relevant information.

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Hi Bin,

Yeah you are right, i could see ttyS1 Enabled in the Prompt. I have to set the Baud Rate for this ttyS1, Im using stty -F /dev/ttyO1 9600 raw -echo this command, but something's not right. I could see no data on the port from my External serial device .

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Ayla Shiva said:
Im using stty -F /dev/ttyO1 9600 raw -echo this command

Are you sure you not using '/dev/ttyS1' here?

Ayla Shiva said:
I could see no data on the port from my External serial device .

I need more details of your setup and test procedure to advise next debug.

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

And please probe the pin P9.24 which is the UART1 TXD pin.

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Yes I'm using ttyS1 in place of ttyO1 in stty -F /dev/ttyO1 9600 raw -echo command.

In Loop back test, its working fine, I could receive and transmit the data.

0 Ayla Shiva over 4 years ago in reply to Ayla Shiva

Intellectual 680 points

Hi BIn Liu,

There was a mismatch of TX and RX cross connection, i swapped, Now I coulld be able to recieve the Data from the Exeternal Device. Thanks a lot for your Help :) :) Appreciate you.

0 Ayla Shiva over 4 years ago in reply to Bin Liu

Intellectual 680 points

Infact I used config-pin -i p9.24 command but wasnt succesfull. it says that config-pin was not found, I've copied the config-pin file from the debian into the BBB, and made it Executable using chmod 777 config-pin command. but still it throws the same error

0 Bin Liu over 4 years ago in reply to Ayla Shiva

TI__Guru**** 175641 points

Hi Ayla,

I am glad it works now. Thanks for the update.

I don't know what the config-pin is, but you don't need it. The pins P9.24 and P9.26 are already configured for UART1 by the pinmux settings in the DT patch I provided above.

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AM3351: Unable to Enable UART in Buildroot Linux Kernel