Atmega128A was locked by me, but it was revived

A simple solution to the problem of accidentally selecting an external RC when programming the fuse bit of the AVR microcontroller, which causes the microcontroller to be locked.

Today,  
I was tinkering with Atmega128A and remembered the fuse bit, so I wrote it in. As
 

a result, this development board can no longer be recognized by the PORGISP software.
 

When it is loaded into flash and the [Auto] button is clicked, an error will be displayed.
 

I am losing money. What should I do if it is locked?
I searched the Internet for answers. There was a brother in a forum who had the same problem as me. His solution was
"The AVR microcontroller with a locked clock can be unlocked by externally inputting a clock of tens of K to 1M to the XTAL1 pin."
"The input clock level needs to be 5V. It does not need to be a square wave. There is a waveform adjustment circuit inside the chip."
"After burning the fuse, you do not need to re-burn the fuse every time you burn the program. You can remove the check mark in the ISP software."
"Just find a clock input to the XTAL1 of the AVR microcontroller."
"Use STM8S105 to program a 100KHz, 5V square wave, then go to ISP to try to modify the AVR fuse, and it's done."


Inspired by his idea, I was considering using the 51 learning board to program a certain pin to generate a square wave, and when it was connected to the XTAL1 of the atmega128A board and shared the same ground with the atmega128A board, I suddenly thought of the 51 development board, and there was a crystal oscillator on the crystal oscillator pin when it was powered on. Why should I program to make an oscillation wave? So I powered on the 51 learning board, shared the same ground with the atmega128A board, and then used a lead to connect a crystal oscillator pin on the 51 board to the crystal oscillator soldering contact point of the atmega128A. The small light on the atmega128A board began to flash, and there was hope. I quickly selected the external crystal oscillator fuse bit in PORGISP and clicked Write. Haha, the atmega128A was reborn.