Am335x UART0 and serial console

SHU LIU

We had a weird problem when running our Beaglebone black board with Linux. We boot the system every 5 minutes.

The UART 0 of Am335x is tied to the serial console of the system by default, and it prints out a lot of logs via serial cable if the cable is connected. The board runs very well when the UART0 is connected with a serial cable.

If the serial cable is not connected, the board would run around 1-6 hours and after that, it can not boot up again.The more logs that we print out on the serial console, the quicker the board goes down and can not boot up again. Rebooting will also print a lot of boot logs on the console.

Would the buffer on UART0 of Am335x side getting full cause the board crashed and not booting up again, since the serial cable is not connected and the UART0 has no outlet?

Is there any way to disable the boot logs when system boots up or to collect those logs?

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

UART0 will transmit regardless of serial cable being connected or not. You should check the state of the UART0_RX signal when the cable is unplugged. If it's low this will cause a Break condition in UART0. Also check if you have the internal pullup resistor enabled in the UART0_RX pinmux.

0 SHU LIU over 9 years ago in reply to Biser Gatchev-XID

Intellectual 570 points

See the image for the circuit on our UART0 side. Actually the board is the Beaglebone black board. We have a buffer on the UART0 and UART0 has a pull down resistor instead of a pull up. The 100k pull down is just to fix the serial port crashing issue.

The voltage on the UART0_RX is 0v. You said that it would cause a break condition in UART0. Can you explain it what kind of condition it is?

Check the internal pullup resister in the UART0_RX pinmux? Should I change it in the device tree or where can I change it?

0 sviss over 9 years ago in reply to SHU LIU

Expert 1530 points

>> The voltage on the UART0_RX is 0v. You said that it would cause a break condition in UART0.

>> Can you explain it what kind of condition it is?

http://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter#Break_condition

The default idle state should be High on both UART RX&TX lines. Why do you use the pull-down, and what is "serial port crashing"?

0 Biser Gatchev-XID over 9 years ago in reply to SHU LIU

TI__Guru**** 393215 points

SHU LIU said:
Check the internal pullup resister in the UART0_RX pinmux? Should I change it in the device tree or where can I change it?

Yes, it should be in the device tree if you are using SDK 7.0.

0 SHU LIU over 9 years ago in reply to sviss

Intellectual 570 points

sviss said:

The default idle state should be High on both UART RX&TX lines. Why do you use the pull-down, and what is "serial port crashing"?

I tried to remove the 100k pull-down, but the RX line was still 0v. How can I change the default state of it?

Why we had the pull-down was because that we want to prevent crosstalk when serial cable is not plugged in.

0 SHU LIU over 9 years ago in reply to Biser Gatchev-XID

Intellectual 570 points

Biser Gatchev-XID said:

Yes, it should be in the device tree if you are using SDK 7.0.

We do not have SDK 7.0. How can we change it? Thanks.

0 Biser Gatchev-XID over 9 years ago in reply to SHU LIU

TI__Guru**** 393215 points

What Linux version do you use?

0 SHU LIU over 9 years ago in reply to Biser Gatchev-XID

Intellectual 570 points

We use Arago project on our board. How can we enable the internal pull up of the UART0_RX pin. It is 0v by default.

0 Miroslav Kiradzhiyski XID over 9 years ago in reply to SHU LIU

TI__Mastermind 25235 points

The TI SDK is based on the Arago project. Are you not using the SDK package? Which kernel version are you using?

Best regards,
Miroslav

0 SHU LIU over 9 years ago in reply to Miroslav Kiradzhiyski XID

Intellectual 570 points

We do not have the TI SDK. We got a Arago root file system from internet. The kernel version is:

Linux am335x-evm 3.12.10-ti2013.12.01 #22 Thu May 8 14:33:47 IDT 2014 armv7l GNU/Linux

How can I pull the UART0_RX pin of the am335x high ?

Regards,

Shu

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Am335x UART0 and serial console