ESP32-WROOM-32 Serial high speed communication error！

[pzh11001]

Board

ESP32 Dev Module

Device Description

ESP32-WROOM-32

Hardware Configuration

ESP32-WROOM-32 and USB data line

Version

latest master

IDE Name

ArduinoIDE

Operating System

WIN10

Flash frequency

80Mhz

PSRAM enabled

no

Upload speed

921600

Description

When the baud rate of serial port is set to 2500000, the transmission data is wrong. However, when the baud rate is set to 3000000, the transmission data is normal! Repeated tests show that the baud rate of 2000000-2300000 is also normal. But every time it is set to 2500000 baud rate, the data will be wrong. No data is lost, but the data becomes other numbers. For example, I test transmission 0x02. However, the host computer sometimes receives 0x02 and sometimes 0x06.

I tested mega2560 with the same code, and everything was normal.

Is there any way to solve this problem?

Sketch

char cc = 0x02;
void setup() 
{
  Serial.begin(2500000);
  delay(10);
}

void loop() 
{
  Serial.write(&cc);
  delay(500);
}

Debug Message

06 02 02 06 02 06 02 02 06 02 02 02 06 02 02 06 06 06 02 06 02 06 02 02 02 02 02 06 02 06 02 06 02 02 02 02 02 02 06 06 02 06 02 02 02 02 02 06 02 06 06 02 02 06 02 06 02 06 02 02 02 06 06 02 02 06 02 02 06 02 06 06 02 02 02 02 02 02 02 02 06 06 02 02 02 06 06 02 02 06 06 06 02 02 02 02 06 06 06 06 06 06 02 06 06 02 02 02 06 06 06 02 02 06 02 06 02 06 02 06 06 02 06 06 02 02 02 02 06 02 06 06 02 06 02 06 06 06 06 06 02 06 06 06 02 02 02 02 02 02 02 02 02 02 06 02 02 06 02 02 06 06 06 02 02 06 06 02 06 06 02 06 06 06 02 06 02 02 02 02 06 02 02 02 02 06 06 06 02 02 02 06 06 06 02 06 02 02 06 02 06 06 06 02 06 06 06 06 02 06 06 02 02 06 02 06 02 02 06 06 06 06 06 02 06 06 06 06 06 06 06 02 06 02 06

Other Steps to Reproduce

No response

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[pzh11001]

When the baud rate 3000000, everything is normal
How odd!

[mrengineer7777]

Wow. 2.5Mhz baud is really fast. Are you sure you need that fast? The higher the baud rate the shorter your communications lines have to be. Also, there are hardware limitations on both devices that limit what baud rates are valid. I don't know what the ESP32 can handle, but I do know that pushing the speed too high can cause signal integrity issues.
Link to baud rate divider issues: https://electronics.stackexchange.com/questions/9264/what-standard-uart-rates-are-there

Ironically, higher baud rates may not give better performance. Some UARTs can shift out a byte really fast, but if you look on a scope there are large gaps between bytes while the UART waits for another byte to be loaded by the processor. Something to consider. Better UARTs implement a small TX buffer, which allows the processor to que up several bytes.

[pzh11001]

Thank you very much. I know that too high baud rate is harmful, but the communication baud rate of the rotary encoder I bought before is 2.5mbps. Therefore, if I want to read the data into esp32, I need the serial port to be able to communicate at the baud rate of 2.5mbps. UART of esp32 supports up to 5mbps baud rate. I have successfully used ATmega2560 for 2.5mbps communication, so I wonder if there are some incompatibilities in the underlying driver of this project, resulting in abnormal high baud rate communication?

[me-no-dev]

I would guess that the hardware just can not divide it's clock to reach 2.5mbps exactly and is actually on the closest frequency it can achieve.

[pzh11001]

okay, thank you. I think I have to use a lower baud rate

[capedra]

@me-no-dev @pzh11001
In my case, whenever I choose 2.5mbps, I get this error while trying to open the serial monitor: "Error: Cannot configure port, something went wrong. Original message: OSError(22, 'Incorrect parameter.', None, 87)". So, the max speed for me is 2.0mbps, not 2.5mbps. And I don't even know why.

[me-no-dev]

@capedra that message comes from you computer's USB-UART driver and not the ESP itself