Unmasking the U-Boot Serial Console: Finding Your UART Number
U-Boot, the ubiquitous bootloader for embedded systems, often communicates with your computer via a serial console. This allows you to interact with the system during boot and perform crucial tasks like debugging. However, pinpointing the exact serial console name and UART number used by U-Boot can be a bit of a puzzle. This article will guide you through the process, providing a comprehensive solution for understanding and configuring your U-Boot serial communication.
Scenario:
You're working on an embedded system that utilizes U-Boot. You need to establish a serial connection to interact with the system, but you don't know the exact UART number or serial console name used by U-Boot. You see a message like "Trying to get console to ..." during the U-Boot startup process, but the console name is missing.
Original Code:
Let's assume your U-Boot configuration file, u-boot.cfg, contains the following lines:
# Serial configuration
# Set the serial console device to use
#setenv consoledev ttyS0
# Set the baudrate of the serial console
#setenv baudrate 115200
These lines are crucial for establishing serial communication. However, without knowing the correct serial console name, it's impossible to connect.
Finding the Missing Pieces:
Here's how to uncover the serial console name and UART number:
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Inspect the U-Boot Source: The
u-boot.cfgfile often includes a line similar tosetenv consoledev ttyS0. This line defines the serial console device used by U-Boot. The 'ttyS0' identifies the device, which usually maps to a specific UART number. -
Examine the Device Tree: For more modern systems using Device Trees, you can find the corresponding UART number in the device tree source file. This file is typically named
u-boot.dtboru-boot.dtsi. Look for entries similar to:serial@80000000 { compatible = "arm,pl011"; reg = <0x80000000 0x1000>; interrupts = <17 0 4>; clocks = <&pl011_clock>; clock-names = "uart_clk"; status = "okay"; pinctrl-names = "default"; pinctrl-0 = <&uart_pins>; uart-has-flow-control; #uart-has-dma; serial-output-enable; #iommu-group; current-speed = <115200>; current-parity = "none"; current-stop-bits = <1>; current-data-bits = <8>; device_type = "serial"; reg-names = "serial"; // ... };In this example, the UART is mapped to
serial@80000000. -
Consult the Board Specific Documentation: The documentation for your specific board will often provide detailed information about the UART configuration, including the device names, UART numbers, and the corresponding pin connections.
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Explore Kernel Device Tree: The device tree used by your Linux kernel can also provide useful information about the UART configuration. This can help you correlate the U-Boot settings with the kernel-level settings.
Example:
Let's say your board utilizes the ttyS0 device name for the serial console. This might map to the UART number 1. You would then use a serial terminal emulator like minicom, screen, or putty to connect to the /dev/ttyS0 device.
Additional Tips:
- If you're having trouble connecting, double-check the baud rate settings in both U-Boot and your terminal emulator.
- Experiment with different serial console devices (
ttyS1,ttyS2, etc.) if the first option doesn't work. - Consult your board's schematic or datasheet for detailed information about the UART configuration.
By following these steps and utilizing the available resources, you can effectively determine the correct serial console name and UART number used by U-Boot, establishing a seamless communication pathway with your embedded system.
References:
