UART Interface on the 40 Pin Header
- If you have the kernel version in the following list, you have to use the Device Tree Overlay to enable the GPIO functions.
- ODROID-N2/N2+: 4.9.230 or above.
- ODROID-C4: 4.9.230 or above.
- Introduction of Device Tree Overlay: https://wiki.odroid.com/common/application_note/software/device_tree_overlay
- How to enable SPI/I2C/UART using Device Tree Overlay: https://wiki.odroid.com/common/application_note/gpio/enable_spi_i2c_uart_with_dtbo
You can use a general purpose UART interface on the 40 pin header on ODROID-N2/C4.
Please see the 40 pin expansion descriptions for N2 or C4 first.
As you can see, with physical pin #8, #10 UART_EE_A and #15, #35 UART_EE_B can be enabled for the alternative UART interface on ODROID-N2.
And, with physical pin #8, #10 UART_EE_A and #15, #33 UART_EE_B can be enabled for the alternative UART interface on ODROID-c4.
Since the default pin function is GPIO-input, you have to change the device tree file to activate the UART mode.
How to use
Enable the feature
- If you enable UART functionality of the pins, you cannot use them as GPIO or the other alternative function.
Basically, the necessary nodes for UART functionality are already defined in the device source tree. Their node names that we're able to use are uart_A and uart_B.
So we just can enable the node we're going to use.
You don't have to make any changes for that file by yourself. Use device-tree-compiler program in Linux system.
Install device-tree-compiler.
- target
sudo apt install device-tree-compiler
First of all, this let's get UART_EE_A to work.
Enter the following command to check if the device tree node for uart_A is enabled.
It should output disabled by default.
ODROID-n2
- target
sudo fdtget /media/boot/meson64_odroidn2.dtb /serial@ffd24000 status # returns disabled
ODROID-C4
- target
sudo fdtget /media/boot/meson64_odroidc4.dtb /serial@ffd24000 status # returns disabled
Enter the following commands to enable that.
ODROID-N2
- target
sudo fdtput -t s /media/boot/meson64_odroidn2.dtb /serial@ffd24000 status "okay" sudo fdtget /media/boot/meson64_odroidn2.dtb /serial@ffd24000 status # returns okay
ODROID-C4
- target
sudo fdtput -t s /media/boot/meson64_odroidc4.dtb /serial@ffd24000 status "okay" sudo fdtget /media/boot/meson64_odroidc4.dtb /serial@ffd24000 status # returns okay
Reboot.
After reboot, you can find the extra ttyS1 device file in the device list.
- target
ls -al /dev/ttyS? # returns crw--w---- 1 root tty 238, 0 May 28 18:36 /dev/ttyS0 crw-rw---- 1 root dialout 238, 1 Jan 29 2018 /dev/ttyS1
In the same way, uart_B can be enabled as changing the status property of serial@ffd23000 to okay.
ODROID-N2
- target
sudo fdtput -t s /media/boot/meson64_odroidn2.dtb /serial@ffd23000 status "okay" sudo fdtget /media/boot/meson64_odroidn2.dtb /serial@ffd23000 status # returns okay
ODROID-C4
- target
sudo fdtput -t s /media/boot/meson64_odroidc4.dtb /serial@ffd23000 status "okay" sudo fdtget /media/boot/meson64_odroidc4.dtb /serial@ffd23000 status # returns okay
If those 2 UARTs are enabled, the devices should list like the below. /dev/ttyS2 is created by enabling UART_EE_B.
- target
ls -al /dev/ttyS? # returns crw--w---- 1 root tty 238, 0 May 29 15:23 /dev/ttyS0 crw-rw---- 1 root dialout 238, 1 Jan 29 2018 /dev/ttyS1 crw-rw---- 1 root dialout 238, 2 May 29 15:28 /dev/ttyS2
Wire cables
4-pin CON5 pin map of our UART(/dev/ttyS0) is,
_____UART____ | | |Pin 4 - GND| |Pin 3 - RXD| |Pin 2 - TXD| |Pin 1 - VCC| |_ | |_________| 3.3V LVTTL
UART_EE_A (/dev/ttyS1)
| J2 Header Pin # | UART Module Pin # | Role |
|---|---|---|
| 9 | 4 | GND |
| 10 | 3 | RxD |
| 8 | 2 | TxD |
| 38 | 1 | VCC |
UART_EE_B (/dev/ttyS2)
| J2 Header Pin # | UART Module Pin # | Role |
|---|---|---|
| 9 | 4 | GND |
| 15 | 3 | RxD |
| 35 (N2)/33(C4) | 2 | TxD |
| 38 | 1 | VCC |
Connect the cables like the following picture, which shows when using UART_EE_A.
The RxD and TxD pins must be twisted together.
ODROID-N2
ODROID-C4
Connect the opposite side of the UART module to your host PC.
Test
- Assume that your host PC is Debian/Ubuntu system.
Enter the following commands to set /dev/ttyS1 up.
- target
sudo stty -F /dev/ttyS1 115200
At your host PC, install minicom to serial communication.
- host
sudo apt install minicom
Check the UART module installed as /dev/ttyUSB*. Then open minicom with the options.
- host
ls /dev/ttyUSB* # results /dev/ttyUSB0
- host
minicom -b 115200 -D /dev/ttyUSB0
At your target board, put something to /dev/ttyS1 device.
- target
echo something | sudo tee /dev/ttyS1
And you can see the message on the minicom screen at your host PC.
joshua