I have a .fex file for Cubietruck. Supposedly, the bluetooth pins are defined in the uart_para2. With the current config, I have uart0 and uart2 enabled, and everything else is disabled. Bluetooth functions fine under such condition.

Then, I changed the .fex file by simply renaming [uart_para2] to [uart_para3] and vice-verca (renaming uart3 to uart2). The new "uart2" (or the old "uart3") is still disabled.

Now bluetooth does not work anymore. dmesg | grep tty still shows that uart3 is mounted on /dev/ttyS1.

So what is UART and why does the label matter? I thought it's a label and nothing more, but evidently not.

1 Answer 1


A UART is a Universal Asynchronous Receiver and Transmitter. It is a device which takes parallel bits of data, as found in the computer, and serializes them to send over a medium such as a wire or the airwaves. It also takes data in in serial form and assembles it into a parallel form to be used in the computer. Here is the Wikipedia article and here is another good explanation. For even more information follow J F Sebastian's link in that page.

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