BeagleBone开发板UART端口数据读取异常问题求助

Hey there! Let’s dig into this weird UART character glitch you’re facing. It’s super odd that a-n comes through perfectly but o-z wraps right back to a-f—this almost always points to a subtle baud rate mismatch, even though both your BeagleBone and PC are set to 115200. Let’s walk through the fixes step by step:

Step 1: Verify UART1’s actual clock source #

UARTs depend on precise clock dividers to hit their configured baud rate. A misaligned clock source can cause tiny cumulative errors that corrupt higher-ASCII characters. Run this command on your BeagleBone to check the clock feeding UART1:

cat /sys/class/tty/ttyO1/device/clock_rate

For 115200 baud (with standard 16x oversampling), ideal clock rates are standard values like 1843200 (1.8432MHz) or multiples like 3686400. If you get a value like 12000000 (12MHz) or 24000000 (24MHz), the divisor calculation is likely off, leading to the character corruption.

Step 2: Check the UART divisor calculation #

Let’s confirm the actual divisor being used to generate 115200 baud. First, install setserial if you don’t have it:

apt update && apt install setserial

Then run:

setserial -g /dev/ttyO1

Look for the divisor value in the output. Calculate the actual baud rate with this formula:
Actual Baud = Clock Rate / (16 * Divisor)
If the result is off by more than 1-2% from 115200, that’s the root cause.

Step 3: Fix the clock via device tree overlay #

BeagleBone’s UART clock settings are controlled by device tree overlays. We need to ensure UART1 is using a standard, baud-rate-friendly clock:

1. Check currently loaded overlays:

   cat /sys/devices/platform/bone_capemgr/slots
   

2. Edit /boot/uEnv.txt to enable the official UART1 overlay (which sets the correct clock):
   Add these lines (remove any existing conflicting UART overlays first):

   enable_uboot_overlays=1
   uboot_overlay_addr0=/lib/firmware/BB-UART1-00A0.dtbo
   

3. Reboot your BeagleBone to apply the change.

Step 4: Explicitly lock in frame settings #

Even if you set 8N1 earlier, system settings can sometimes override these. On your BeagleBone, run this to force the correct frame configuration:

stty -F /dev/ttyO1 115200 cs8 -cstopb -parenb

This explicitly sets 8 data bits, 1 stop bit, no parity, and 115200 baud. Double-check your PC’s terminal settings too—make sure flow control (hardware/software) is disabled, as this can cause unexpected behavior even if baud rates match.

Step 5: Run a loopback test to isolate the issue #

Before reconnecting to your PC, do a quick loopback test on the BeagleBone: connect the TX and RX pins of UART1 together. Then send data from the BB to itself—if you still see corrupted o-z characters, the problem is definitely on the BB side (clock/configuration), not the PC or wiring.

内容的提问来源于stack exchange，提问作者Revathi M