AcSiP AI7688H Reference Manual page 23


if you also want to change the baudrate, please modify the file
include/configs/rt2880.h
#define SERIAL_CLOCK_DIVISOR 16
#define CONFIG_BOOTDELAY
#define CONFIG_BAUDRATE
#define CONFIG_SERVERIP 10.10.10.3
#define CONFIG_IPADDR 10.10.10.123

Change this:
#define CONFIG_BAUDRATE

to this (change the baudrate from 57600 to 115200 as an example):
#define CONFIG_BAUDRATE

This will then change the bootloader console baudrate from 57600 to
115200

Now build the bootloader and upload it to the board
1
57600
57600
115200
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Document Name AI7688H
Reference Manual
Version V 2.0
Date 2019/08/08