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By the end of this section, you will gain experience in the following topics:
  • Establishing a serial port connection between the developer’s computer and the Gemstone board using a USB TTL cable.
  • Communicating between both computers via a terminal.
  • Preliminary preparation for the t3gemstone/examples/serial project.
A serial port is a communication channel that enables data transmission between devices such as computers and microcontrollers. This communication typically occurs via the UART (Universal Asynchronous Receiver-Transmitter) protocol and is ideal for low-speed data transmission. For example, serial ports are often preferred when communicating with external modules like GPS or Radio Transmitters.

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Serial Port Interfaces

The serial port interfaces on the T3-GEM-O1 card are listed in the table below.

Todo: Pins where the seriport connection can be made

GPIO (RX)GPIO (TX)
UART-MAIN0ttyS2Serial HeaderSerial Header
UART-MAIN1ttyS3GPIO-15GPIO-14
UART-MAIN6ttyS6GPIO-4GPIO-17k3-am67a-t3-gem-o1-uart-ttys6.dtbo
UART-WKUP0ttyS0GPIO-7GPIO-24k3-am67a-t3-gem-o1-uart-ttys0.dtbo
  • Access to the Linux terminal is obtained from the UART‑MAIN0 serial port.
  • When the k3-am67a-t3-gem-o1-pwm-epwm0-gpio5-gpio14.dtso overlay is enabled, the UART‑MAIN1 TX pin is disabled, while the RX pin continues to function normally.
  • Bluetooth becomes disabled when the UART‑MAIN6 serial port is activated.
The names of the overlay files for the interfaces to be enabled must be added to the overlays variable in the /boot/uEnv.txt file. Detailed information about overlays can be found in the Device Tree section.

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Serial Port Usage

1

SSH/VNC Connection

Connect to the development board using one of the methods: SSH or VNC.
2

Shell

Create Bash Shell scripts.
3

TTL and Terminal

Connect the developer’s computer and the Gemstone board using a TTL cable and perform data exchange via the Tabby.sh terminal.

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1. Creating a Shell Script

Create a script file for opening the serial port and sending data. 
touch serial-test.sh

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2. Using a Text Editor

Open the serial-test.sh file using the nano text editor from the terminal interface. 
nano serial-test.sh
After copying the following code, paste it into the serial-test.sh file. 
#!/bin/bash

SERIAL_PORT="/dev/ttyS3"
BAUD_RATE="115200"

stty -F /dev/ttyS3 115200 -crtscts

while true; do
    echo "Teknofest" > $SERIAL_PORT
    sleep 1
done
Press CTRL+X, then press Y to save and exit the nano editor.

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3. Running the Shell Script

Make the serial-test.sh file executable using the chmod command and start it. 
chmod +x serial-test.sh
./serial-test.sh

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4. Communication