How to enable hardware flow control (rs485)?

ASido · ‎2020-03-23

I am using the STM32MP157C-DK2 board. I fixed the stm32mp157a-dk1 file as shown below

Generated the device tree blobs (* .dtb) and updated the device tree blob on the board.

I sent an echo "hello!" > /dev/ttySTM1

and I see that the RTS pin is held for too long, I think that this pin is held all the time while the file is open by the operating system.

Then I launched the Modbus-RTU test application. reception and transmission work correctly, but the RTS pin does not switch. The RTS pin was pressed to the ground when I launched the application and released when I closed the application.

How to enable hardware flow control (rs485)?

ASido · ‎2020-03-25

I found the answer here https://www.kernel.org/doc/Documentation/serial/serial-rs485.txt. it was necessary to fill out the rs485conf structure and call ioctl (fd, TIOCSRS485 and & rs485conf)

View solution in original post

Olivier GALLIEN · ‎2020-03-23

Hi @ASido

As first assumption your problem looks similar to this post :

https://community.st.com/s/question/0D50X0000BQOvVxSQL/cant-get-the-rts-line-working-on-stm32mp1-in-linux-stm32mp157cdk2

"st,hw-flow-ctrl;" properties missing in your Device Tree ?

Can you please tell me which version of OpenSTLinux you are using ?

Thanks,

Olivier

Olivier GALLIEN
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ASido · ‎2020-03-23

Hi OlivierG (ST Employee)

>As first assumption your problem looks similar to this post :

https://community.st.com/s/question/0D50X0000BQOvVxSQL/cant-get-the-rts-line-working-on-stm32mp1-in-linux-stm32mp157cdk2

yes i saw this post

>"st,hw-flow-ctrl;" properties missing in your Device Tree ?

yes, it was seen in my question

>Can you please tell me which version of OpenSTLinux you are using ?

1.2.0

I did as it is written here: https://wiki.st.com/stm32mpu/wiki/Serial_TTY_device_tree_configuration#Activation_of_a_USART_or_UART_instance and https://wiki.st.com/stm32mpu/wiki/How_to_use_TTY_with_User_Terminal#Purpose

Reception and transmission are working correctly, but the RTS output is not working properly. this can be seen in the screenshots in my question

ASido · ‎2020-03-25

I found the answer here https://www.kernel.org/doc/Documentation/serial/serial-rs485.txt. it was necessary to fill out the rs485conf structure and call ioctl (fd, TIOCSRS485 and & rs485conf)