High CPU load

[holgerlembke]

Describe the problem

When opening the serial monitor, serial-monitor.exe creates a relatively high CPU load.

It seems to be related to a certain board type: esp8266 (3.1.2 https://arduino.esp8266.com/stable/package_esp8266com_index.json).

If I select a different board type, the load is gone.

Something is pumping data, as far as I can see, there is a thread continuously moving data.

To reproduce

(see above)

Expected behavior

(see above)

serial-monitor version

0.14.1

Operating system

Windows

Operating system version

10.0.19045.5487

Additional context

Discussion: https://groups.google.com/a/arduino.cc/g/developers/c/PqosKNzu2GU

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the latest version
• My report contains all necessary details

[holgerlembke]

Sidenote: I tried to replace the serial-monitor.exe with my own application (written in C#).

But it is not loaded at all. Why? golang magic?

[cmaglie]

Hi @holgerlembke, thanks for the bug report, and sorry I didn't have the time to look at this yet.

But it is not loaded at all. Why? golang magic?

It's a plain executable it should start normally...

[xxxajk]

Certainly there should be some sort of win equivalent to Linux select() which can check for traffic.

What I have done in anything in my own Linux code (in C), is to do a check with select() with a zero timeout, and if no data, a 1mS sleep() (or other processing for single thread, in which case both have to fail for the sleep()), which always lowered the CPU to nearly zero, and never lost any data, since it can handle 1mS of burst in a single gulp, even at very high speeds.

[holgerlembke]

no need to hurry, it is not that important.

Just revisited my code... Fixed some very stupid errors, now it is loaded. I think I will spend some time of the weekend with recreating that thing in c#.

[holgerlembke]

@xxxajk I have no clue about golang, but I would expect a read-function from stdio to pass it to the OS and that should let it wait with zero load. Isn't that so?

[xxxajk]

@xxxajk I have no clue about golang, but I would expect a read-function from stdio to pass it to the OS and that should let it wait with zero load. Isn't that so?

Unsure, but I do know that in order to make programs not eat cycles on linux in C, that using select and sleep on fails was able for some code that I wrote back in about 1995 running on a 386sx totally fine, even when the data was streaming in from 10baseT bidirectionally to/from high-speed UART. Never wrote anything in golang either, but then I'm kind of a control freak when it comes to what's actually running on the CPU, to the point that I have mixed C and ASM a lot...

[per1234]

Hi @holgerlembke.

If I select a different board type, the load is gone.

I'm not sure I understand what you mean by "select a different board type".

Do you mean that you are only selecting a different board from Arduino IDE's Tools > Board menu, without changing the Tools > Port menu selection? If yes, please tell us which exact Tools > Board menu item you have selected when the fault occurs, and which exact Tools > Board menu item you have selected when the fault does not occur.

Or do you mean that you connect a different board to your computer and select that board and port instead of the board and port of the ESP8266-based board? If yes, please tell us exactly which board you are using when the fault occurs, and which one you are using when the fault does not occur.

[holgerlembke]

@per1234

I just rechecked it and my observation was wrong. Whatever board I select, load is there.

I edited the bug report.

[per1234]

Thanks for the clarification. Please tell us which USB to serial bridge chip your Arduino board has. This is a black chip near the USB socket.

The chip will usually be identified by writing on the top. This might say something like "WCH CH340G" or "SILABS CP2102".

Examples:

WCH CH340

📷

SparkFun - CC BY-SA 4.0 (cropped)

There are some boards on the market that have a USB chip with the same IC package as the WCH CH340, and which are identified by the computer as a CH340. However, these chips don't have the "WCH CH340C ..." labeling like you see on the chip in the picture above:

📷

NodeMCU Lua Lol1n V3.jpg by Popolon - CC BY-SA 4.0 (cropped)

Silicon Labs CP2102

📷

SparkFun - CC BY-SA 4.0 (cropped)

---

If it isn't clear, alternatively you can provide the link to where you bought the board from and we'll see if we can determine the chip from the product listing.

[holgerlembke]

Device manager says CH340. Chips says CH340C.

Just added a board with a cp9102. It does NOT show the high load.

On a sidenote, my own C# serial-monitor shows traffic even after closing the serial port from the IDE. Not sure about how, why and when... could be my error, needs more research

[per1234]

Is your board running a sketch that causes it to produce serial output?

Note that the ROM bootloader of the ESP8266 produces output on startup or reset, so in cases where either the sketch code or electrical conditions (e.g., insufficient power supply) causes the board to continuously crash/reset, it is also possible that the board can produce continuous serial output even if there isn't anything in the sketch code that explicitly does so. In this case, you should see the output in the Arduino IDE Serial Monitor if you select "74880" from the baud rate menu in the Serial Monitor panel (the bootloader uses this baud rate even if the sketch is configured for a different rate).

[holgerlembke]

This

void setup() {}
void loop() {}

produces the load.