Is it RS485 supported with i.MX6 ?

[marcocavallini]

I am using a linux kernel-3.10.17 and I'm trying to communicate using UARTS on a i.MX6S CPU.

I am using RS485 adapters and the problem is that the RTS signal is always high when I transmit and receive.

I noticed that this is a FAQ in the community website but there is no answer neither solution.

I wonder if the RS485 protocol is currently supported or not.

Thank you.

[igorpadykov]

Hi Marco

current driver doesn't support RS485 mode, it may be useful

link below

i.MX6 UART Driver and RS485 Support

Best regards

igor

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[marcocavallini]

Hi Igor,

Thank you, I had already seen that link, unfortunaltely it manages the CTS signal but RS485 need to move the RTS as well suring the transmission.

Reading the datasheet I noticed that i-MX6 is not able to drive the RTS internally, so the only way that I see is to manage RTS as regular GPIO from inside imx.c

Do you know a better solution?

Best regards,

Marco

[EricNelson]

Hi Marco,

Uwe Kleine-König recently pushed patches to the main-line driver for the i.MX UART to support RS-485 transmit-enable using the RTS line:

     https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/drivers/tty/serial/imx.c?id=...

[marcocavallini]

Hi Eric,

thank you for this hint, it looks promising.

Do you know to which kernel version does it apply to?

[EricNelson]

Hi Marco,

You can use the navigation links in the git URL above to get a picture of the tree as of that commit, and if you navigate to the top level Makefile, you'll see that it was applied after 4.0.0-rc2:

https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/Makefile?id=17b8f2a3fdca29a9b2...

[marcocavallini]

Hi Eric,

I adapted that patch to my imx kernel-3.10.17.

Unfortunately it doesn't drive the RTS down during transmission, I think this is a lack in the CPU logic.

[igorpadykov]

Hi Marco

IMX6DQRM sect.64.13.2 Programming the UART in 9-bit RS-485 mode

shows RS485 programming, I believe there is no better solution.

In general it is possible to use GPIO to control RS-485 output driver.

Best regards

igor