setCpuFrequencyMhz() changes Serial bauds if frequency<80Mhz

[Leonleon33]

Board

ESP32 Dev module

Device Description

ESP32 Dev module alone

Hardware Configuration

Nothing

Version

v2.0.1

IDE Name

Arduino IDE

Operating System

Ubuntu 20.04

Flash frequency

80Mhz

PSRAM enabled

no

Upload speed

921600

Description

When setting CPU frequency below 80Mhz, the serial monitor is garbage until I change the baud rate...
I manage to solve the problem by setting the Serial.begin(bauds) to : 80 / cpufreq * monitor_bauds
See sketch attached.

Sketch

uint32_t Freq = 0;
const int bauds = 115200;
int my_bauds;
int cpufreqs[6] = {240, 160, 80, 40, 20, 10};
int i = 0;

void setup() {
  Freq = getCpuFrequencyMhz();
  if (Freq < 80) {
    my_bauds = 80 / Freq * bauds;
  }
  else {
    my_bauds = bauds;
  }

  Serial.begin(my_bauds);        // Attention dépend de la frequence CPU si elle est <80Mhz 
  delay(500);
  //
  Freq = getCpuFrequencyMhz();
  Serial.print("CPU Freq = ");
  Serial.print(Freq);
  Serial.println(" MHz");
  Freq = getXtalFrequencyMhz();
  Serial.print("XTAL Freq = ");
  Serial.print(Freq);
  Serial.println(" MHz");
  Freq = getApbFrequency();
  Serial.print("APB Freq = ");
  Serial.print(Freq);
  Serial.println(" Hz");
}
void loop() {
  Serial.print("\nchange CPU freq to ");
  Serial.println(cpufreqs[i]);
  delay(1000);
  setCpuFrequencyMhz(cpufreqs[i]);
  Freq = getCpuFrequencyMhz();
  Serial.print("Send to serial with my_bauds = ");
  Serial.println(my_bauds);
  Serial.print("CPU Freq = ");
  Serial.print(Freq);
  Serial.println(" MHz");
  //  Change bauds rate ?

  if (Freq < 80) {
    my_bauds = 80 / Freq * bauds;
  }
  else {
    my_bauds = bauds;
  }
  Serial.end();
  delay(1000);
  Serial.begin(my_bauds);
  delay(1000);
  Serial.print("\nchange my_bauds to ");
  Serial.println(my_bauds);
  Serial.print("Serial set to ");
  Serial.println(my_bauds);
  Serial.print("CPU Freq = ");
  Serial.print(Freq);
  Serial.println(" MHz");
  Serial.print("my_bauds = ");
  Serial.println(my_bauds);

  delay(1000);
  i++;
  i = i % 6;
}

Debug Message

No debug message, just monitor output set to 115200
CPU Freq = 240 MHz
XTAL Freq = 40 MHz
APB Freq = 80000000 Hz

change CPU freq to 240
Send to serial with my_bauds = 115200
CPU Freq = 240 MHz

change my_bauds to 115200
Serial set to 115200
CPU Freq = 240 MHz
my_bauds = 115200

change CPU freq to 160
Send to serial with my_bauds = 115200
CPU Freq = 160 MHz

change my_bauds to 115200
Serial set to 115200
CPU Freq = 160 MHz
my_bauds = 115200

change CPU freq to 80
Send to serial with my_bauds = 115200
CPU Freq = 80 MHz

change my_bauds to 115200
Serial set to 115200
CPU Freq = 80 MHz
my_bauds = 115200

change CPU freq to 40
�f⸮⸮⸮`                 AND OTHER GARBAGE
change my_bauds to 230400
Serial set to 230400
CPU Freq = 40 MHz
my_bauds = 230400

change CPU freq to 20
�f⸮⸮⸮`                 AND OTHER GARBAGE
change my_bauds to 460800
Serial set to 460800
CPU Freq = 20 MHz
my_bauds = 460800

change CPU freq to 10
�f⸮⸮⸮`                 AND OTHER GARBAGE
change my_bauds to 921600
Serial set to 921600
CPU Freq = 10 MHz
my_bauds = 921600

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.

[SuGlider]

Thanks @Leonleon33 for reporting and solving the issue with your example.
The issue will be solved with the PR #6037
Great Job!

[savejeff]

I encounter the same problem.
I was able to fix this in the same way.
Is the fix maybe not published on the main branch?

these are the firmware versions I'm using:

framework-arduinoespressif32 @ 3.20004.0 (2.0.4)
 - tool-esptoolpy @ 1.30300.0 (3.3.0)
 - tool-mkfatfs @ 2.0.1
 - tool-mklittlefs @ 1.203.210628 (2.3)
 - tool-mkspiffs @ 2.230.0 (2.30)
 - toolchain-riscv32-esp @ 8.4.0+2021r2-patch3
 - toolchain-xtensa-esp32s3 @ 8.4.0+2021r2-patch3

through PlatformIO with
platform = espressif32@5.1.0

with ESP32-S3

[SuGlider]

This PR is already merged and it is part of Arduino Core 2.0.2+
About PlatformIO, it is already in latest realease.
https://github.com/platformio/platform-espressif32/releases

[savejeff]

But why do i then need to ajust the baudrate in the way that was proposed by the issue creator?

What I'm doing is going into a different mode that is something like a standby mode. when setting a CpuFrq below 80Mhz i have to update the baudrate accordingly.

It also seems like I2C and SPI clocks are also slowed down. SD Card writes also stop working after the reduction of the CPU clock

[SuGlider]

If necessary, please open a new issue clarifying the Arduino Core Version, if this issue occurs with Arduino IDE, what is the SoC (ESP32 or the S2/S3/C3) and so on. Describe your issue and then add a minimum sketch that can be used to reproduce the issue.

[savejeff]

I have already supplied all these information. The original sketch provided by the Issue opened still works with the latest Arduino 2.0.4 and ESP32-S3 Devkit C-1.

But ill open a new issue

[kjw3898]

I have already supplied all these information. The original sketch provided by the Issue opened still works with the latest Arduino 2.0.4 and ESP32-S3 Devkit C-1.

But ill open a new issue

try this when change cpu frequency

 
Serial.begin(115200); // first init serial 
// ...  your code
Serial.end();    // when change cpu frequency
setCpuFrequencyMhz(40);
Serial.begin(115200);