ESP32 Forum

Strictly referring the official design of module ESP32-S2-WROOM, I designed my own small WIFI board by the chip ESP32-W0WD. But I failed to download my program to flash. The flash tool complains that:  Flash synchronization error.  
My BSL programming tool is : flash_download_tools_v3.6.8.exe and the hardware tools is USB-UART
IO0 was configured as low power Level
EN pin is configured as high

Hard to say.

- If you boot up the board normally and run a terminal emulator on the serial port, do you see any output?
- Can you confirm the 40MHz crystal is doing something?

I am sure the 40MHz crystal is working normally.

And the other half of my post? If you boot up the board normally and run a terminal emulator on the serial port, do you see any output?

Also, note that EN should be low for a while on power-up; you can't just tie it to 3.3V.

Will the serial port of the circuit board without any program also have output? When the program is burning, the oscilloscope can see the data packet that the upper computer communicates with the lower computer, but the lower computer does not respond, and the flash is used for burning. When using the flash tool, the flash is not detected

Given that GPIO15 is unconnected or pulled high, the ESP32 should output a line or two indicating the ROM version and reset reason as soon as it starts up.

I had not seen nothing in serial port

Hmm, the 40MHz likely indicates that the chip does have power, but the lack of a serial port signon message is a symptom... Do you happen to have a schematic for the board we can take a look at?