Serial Monitor update rate issue.

[cl330b]

The Serial Monitor built in to the IDE has a significantly delayed update rate.

I am using the Arduino Zero. I am using the following to print serial information to the internal Serial Monitor and an external bit of software (GTKTerm v1.1) to monitor the serial information being written to the native USB port.

Serial.begin(115200); SerialUSB.begin(115200);

1. Open built in Serial Monitor.
2. Open external Serial Monitor.
3. Open scope to view which output is currently active.
4. View lag in the built in Serial Monitor.
5. Compare the lag with an external Serial Monitor.

I would expect to see the update rate of the built in Serial Monitor match the modulated outputs of the microcontroller. I am using a scope to view the outputs of the Zero. I can see in real time which outputs are on compared to the built in Serial Monitor and the external Serial Monitoring software.

(Please see attached screenshots for context.)

Version Information:
Linux 5.8.0-31-generic arduino/arduino-pro-ide#33-Ubuntu SMP Mon Nov 23 18:44:54 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
arduino-pro-ide_nightly-20201211_Linux_64bit

Additional Information Regarding Issue
When I hold the board in reset, the built in Serial Monitor continues to update as if still reading incoming serial data.

-cl330b

[cl330b]

When I slow the code down, the Serial Monitor can keep up. In the above screenshots I was writing a serial message every 1.37mS (0.00137sec). I have slowed the code down to write to serial every 1000mS (1sec). The time it takes to print the characters on the built in Serial Monitor takes a bit longer than one full second to print roughly 24 characters (including spaces).

Screenshots

Note
Please let me know if there is something specific I can dig into to provide more information.

[kittaakos]

Please let me know if there is something specific I can dig into to provide more information.

Well, I doubt this issue belongs here but since you have taken the time to precisely submit the details, I leave it open. Perhaps someone with better domain knowledge can decide if this is something we have to work on or not.

CC: @ubidefeo

[ubidefeo]

hi @cl330b

thank you so much for going through the effort of connecting your DSO, tells us you've done more than we expect when it comes to feedback. 💯

We have received another report of the serial monitor not able to keep up arduino/arduino-pro-ide#400 and this is definitely something that needs work, especially as we work towards faster devices having to provide serial monitor output.

We'll keep this one open and provide updates in the weeks to come, but we have quite a list of things that need to be worked on before we tackle the Serial Monitor

Hope to have updates soon
u.

[toogooda]

Hi, can I please add that while the Serial monitor is struggling to keep up if effects the performance of the editor, with things like Auto complete; auto indent and even Ctl+T not working.
I have to slow Serial down to 4800 board before the ide could keep up and allow debugging using Serial near real time.
In my example where I simple displayed an incrementing unsigned long then hit reset at 3000 shown onn the screen it continues to count up to over 6000.

unsigned long a=0;

void setup() {
  Serial.begin(4800);
}

void loop() {
  Serial.println(a);
  a++;
}

[pavel-b-kr12]

very bad performance at speed more than 57600
void loop() {
Serial.println(1);
}
cause UI slowdown and progressive increasing lag before show new data in terminal. Firstly I even thought my software did not working because terminal shows very old data

[ubidefeo]

@pavel-b-kr12
can you try Beta 4 and if you still have the issue test the Nightly Build?
I know we have implemented a couple fixes for this but not sure they made it into release yet

[toogooda]

Beta 4 no improvement that I can see. will try nightly build.

[toogooda]

Tested nightly build seems to be a bit quicker but still unusable above 9600 :(
Some low speed serial output now OK
baud-----Serial Keep up
300-------Yes
1200------Yes
2400------Yes
4800------Yes
9600------No - but close
19200-----No
38400-----No
57600-----No
115200----No

unsigned long a=0;
void setup() {
  Serial.begin(4800);
}

void loop() {
  Serial.println(a);
  a++;
}

@ 115200 If I let it run for one second then hold reset it keeps scrolling for another 9-10 seconds

Note: because of Timezone this might be nightly build n-1

[ubidefeo]

@toogooda
I'll investigate with the team tomorrow if that fix is on track :)