Cannot use uart 3 on the second header

#1

I cannot use uart 3 one the second header. The Rock Pi S is V1.3. mraa-uart cannot detect uart3 and picocom cannot show signal from ttyS4. Linux distro is Ubuntu.
Following is the info:

sudo dmesg | grep serial
[ 0.400911] ff0a0000.serial: ttyS0 at MMIO 0xff0a0000 (irq = 12, base_baud = 1500000) is a 16550A
[ 0.479839] ff0b0000.serial: ttyS1 at MMIO 0xff0b0000 (irq = 13, base_baud = 5078125) is a 16550A
[ 0.481655] ff0c0000.serial: ttyS2 at MMIO 0xff0c0000 (irq = 14, base_baud = 5078125) is a 16550A
[ 0.483624] ff0e0000.serial: ttyS4 at MMIO 0xff0e0000 (irq = 15, base_baud = 5078125) is a 16550A
[ 3.829327] systemd[1]: Created slice system-serial\x2dgetty.slice.

sudo mraa-uart list

  1. /dev/ttyS0 1500000 8N1 (none) (none)
  2. /dev/ttyS1 9600 8N1 (none) XONXOFF
  3. /dev/ttyS2 9600 8N1 (none) XONXOFF
  4. ---- error reading uart information ----
#2

@Jing_Guo I face the same question,have you solved it?

#3

I have solved this problem
add “rk3308-uart3.dtbo” to the path
/boot/dtbs/4.4.143-65-rockchip-g58431d38f8f3/rockchip/overlay/

rk3308-uart3.zip (425 Bytes)

How to enable uart3 on Rock pi S?
Rock PI S dtb issue