UART0 hardware flow control

Tagged: uart hardware flow control

This topic has 2 replies, 2 voices, and was last updated 5 years, 2 months ago by slisgrinder.

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- September 18, 2019 at 7:42 pm #9083
  slisgrinder
  Participant
  Greetings,
  I was wondering if there was any way to test the hardware flow control for UART0? Im referring to RTS/CTS lines (balls C13/C12). I have already diverted the console output of the kernel to ttyS2 and disabled the getty service. We have a custom board and wanted to use UART2 with its hardware flow control but unfortunately the RTS/CTS pins are shared with I2C0 which is connected to the PMIC and EEPROM inside the SiP.
  I am using the latest “console” image from elinux and the hardware is based on the RED development board:
  https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Debian_Stretch_Console_Snapshot
  “bone-debian-9.10-console-armhf-2019-09-08-1gb.img.xz”
  Linux beaglebone 4.14.108-ti-r116 #1 SMP PREEMPT Wed Sep 4 21:44:30 UTC 2019 armv7l GNU/Linux
  U-Boot 2019.04-00002-gbb4af0f50f (Jul 08 2019 – 11:44:39 -0500), Build: jenkins-github_Bootloader-Builder-128
  Any insight is appreciated.
  Regards,
  Kartik
- September 19, 2019 at 12:58 pm #9085
  Neeraj Dantu
  Moderator
  Kartik,
  I am assuming the flow control pins for UART0(C12/C13) are accessible on your custom board. Hardware flow control is supported in omap uart driver.
  You should be able to test hardware flow control for UART. First, you will have to set pin multiplexing for these pins in your device tree. You should add pin mux details of C12 and C13 her: https://github.com/RobertCNelson/dtb-rebuilder/blob/4.14-ti/src/arm/am335x-bone-common.dtsi#L92
  Please see application notes regarding device tree for help:
  Pin multiplexing for OSD335x: https://octavosystems.com/app_notes/osd335x_pinmux/
  Device tree tutorial: https://octavosystems.com/app_notes/osd335x-design-tutorial/osd335x-lesson-2-minimal-linux-boot/linux-device-tree/
  For testing, please take a look at: http://processors.wiki.ti.com/index.php/Linux_Core_UART_User%27s_Guide. You can also create a test environment by setting up your board as transmitter and pull down the CTS pin to GND to see if the processor stops communication.
  Best,
  Neeraj
- September 19, 2019 at 9:26 pm #9106
  slisgrinder
  Participant
  Good evening Neeraj,
  Thanks for the info. I managed to get RTS/CTS defined and enabled in am335x-boneblack-uboot-univ.dtb. In the spirit of product development I already ran into another issue but that’s on our end.
  Thank you for your help!
  Regards,
  Kartik
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