Author Topic: UART Garbage?  (Read 4152 times)

Offline Deschain

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UART Garbage?
« on: November 30, 2013, 01:53:33 pm »
Hello there,

The main reason because I bought a cubieboard was that I was unable to install GNU/Linux in another SoC I have. It's one of those many Android TV boxes with an Amlogic AML8726-M (Meson-M1).

At first I though I would be easy because even though the seller (Airis) has no support, Amlogic have a site with some information, documentation and sources.

To the point, when I tried to access by the UART to the boot process (u-boot seems to be the standard in all these devices and boot from a SD card) it seemed that all I could read was garbage. Although I had Amlogic UART configuration I tried several more with no result. After some time I realize that most documentation from Amlogic is in Chinese so maybe it was no garbage but other charset (instead of latin-1 or the default in Putty) so I tried the well known UTF-8 (as I found to be the right charset for these cases) and then I could read some information, some Chinese chars but that was it all... I could no send any data to stop the boot process and access the u-boot "console"

So my question is if anybody has crossed this problem before or if anybody has any suggestion because I would like to mess up with this device

Offline patwood

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Re: UART Garbage?
« Reply #1 on: November 30, 2013, 02:04:05 pm »
Just on important point: do you have ground connected as well as rx and tx?

Also, they might have locked down u-boot by disabling the autoboot countdown.

Offline Deschain

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Re: UART Garbage?
« Reply #2 on: December 01, 2013, 02:17:51 pm »
The UART port is kind of strange because it has Tx, Rx and two GND (will include picture). I tried almost all possible combinations just in case the labelling is wrong and of course with and without GND (each pin and both of them, maybe it needs a reference for both Tx and Rx, don't have the scheme). I could read some data with just one GND, Tx and Rx connected (as usual).

First I tried with an USB to UART TTL/COM adapter with the chip CP2102 which I have used before without any problem and when I bought the cubieboard I also tried with its adapter, but same problem...

And the auto boot countdown it's enable because it appears in the boot process (will include dump).

So basically I think that it may be a problem with Chinese charsets and I don't know how to figure this out...

P.S. Don't have JTAG or know Chinese to read the poor documentation they provide

Offline diogoc

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Re: UART Garbage?
« Reply #3 on: December 02, 2013, 04:24:05 am »
Are you using the correct baudrate, parity, stop bits?

Offline Deschain

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Re: UART Garbage?
« Reply #4 on: December 02, 2013, 10:23:52 am »
Are you using the correct baudrate, parity, stop bits?

Yeap (according to the manufacturer)

Although I had Amlogic UART configuration