Could a Serial Read Buffer on my ESP8266 be overblown ?

[tolga121]

Hi to the world

could someone please help me out on my question ?

If my main ESP8266 receives constantly a Serial.print from a second ESP8266, and if my main ESP do not use the

while (Serial.available() > 0){}

could the buffer than be overblown ? And than with an overblown buffer the RAM works very sloly ?

Or does is the receiving ESP8266 just ignoring the incoming Serials ?

And what about the Serial Output ? Could it be overblown too ?

Thanks mates

@UKHeliBob @Paul_B

[tolga121]

Okay, and where is the buffer located ? In the RAM ? Or is there a particular place only for the SerialBuffer in ESP8266 ?

I am asking this, because I fear that the other ram is filled up quickly when the buffer is on the "normal" ram located.

[camsysca]

@tolga121

In the RAM

Yup. Has to be RAM, it's being written to.
You need to tell us more about your application. While it's true your buffer won't overrun other memory, it's entirely possible you're getting corrupted messages due to full buffer issues; it's also possible your source device has a full output buffer, which will slow it down tremendously, but which may look like a problem with your receiving device.

[tolga121]

@camsysca

You need to tell us more about your application.

It's a simple Communication between two ESPs. I just wanted to understand how the buffer works. Because it could be importand to understand the serial buffer for future projects.

@camsysca

it's also possible your source device has a full output buffer, which will slow it down tremendously

Okay. So a full output-buffer from source, would slow down the receiving ESP ram, right ?

@Delta_G

There's also the possibility that while the serial buffer itself can hold the data, your parsing code may be leaking memory or overrunning a string buffer.

Okay, this would be no problem, because the sending data are only small words (no huge text)

[camsysca]

Okay. I'll throw in some speculation, as you're not sharing.

1. Source is transmitting at 9600, but sending more than 1000 chars/second. Source quickly fills it's transmit buffer, then slows to a crawl while the outgoing characters go; when each character is transmitted, there's room for one more in the buffer, so it crawls. This is why Serial transmit can be considered to be a 'blocking' code, in some circumstances but not others.
2. Source is transmitting at a high baud rate, and sending a lot of data, but the transmit buffer is keeping up. The code in the receiving device is unable to keep up(emptying the buffer and processing the data), so the receive buffer fills. Once it's full, what is the receiving code going to do? No, it doesn't go rogue and write to other memory. Instead, it overwrites the stalest data in it's buffer. This is guaranteed to mangle incoming messages.
3. Some glorious combination of both of the above, which will result in confusion when you fix one side, but not the other.
   Since we know exactly zero about the details of sender and receiver, all of the above may be totally irrelevant. Or not.

[gfvalvo]

The whole discussion is a pointless waste of time until @tolga121 posts the actual code as there's a 100% chance that's where the problem lies.

[tolga121]

@camsysca

Source is transmitting at 9600, but sending more than 1000 chars/second. Source quickly fills it's transmit buffer, then slows to a crawl while the outgoing characters go; when each character is transmitted, there's room for one more in the buffer, so it crawls. This is why Serial transmit can be considered to be a 'blocking' code, in some circumstances but not others.

absolute understandable, thanks. This is exactly what I wanted to hear So I will use other methods for the Serial (see below in this post)

@Delta_G

If the output buffer is full at the sender then the sender will slow way down which will slow down the serial transmission. Depending on how the ESP code we still haven't seen is written, that may or may not slow it down as well.

Yes, this is exactly what I wanted to hear... thanks mates

@gfvalvo

The whole discussion is a pointless waste of time until @tolga121 posts the actual code.

I have no actual code. I just wanna learn how to handle with the ESP (and other electronics)

But I will post a code, how I would handle a Communications between two ESPs... so wait a little..

[camsysca]

@tolga121

I have no actual code.

Yep. That's what I parsed from your earlier comment. If you had said that upfront, we could have focused on the theory. As it was, it sounded like the typical question posted here, where we have to slowly extract the real context in order to determine where something's gone awry.
Anyway, glad you've got what you wanted. I look forward to your proposed handling description.

[tolga121]

Okay guys, as a positive example of code how to spare the RAM.

Do you guys agree ?

this is the sender code

// ESP number 1

#include <ESP8266WiFi.h>

int DataAlreadSent=0;

void setup() {
  Serial.begin(115200);
}

void loop() {
  
  if (DataAlreadSent == 0)
  { 
    Serial.print("Hello");
    DataAlreadSent=1; // so this indicates, that the data is already sent
  }

}

and this the receivers code

// ESP number 2

#include <ESP8266WiFi.h>

int DataAlreadyReceived=0;

String mystring, combined;

void setup() {
  Serial.begin(115200);
}

void loop() {
  
  while (Serial.available() > 0)
  { 
    char receivedChar = Serial.read();
    String mystring(receivedChar);
    combined = combined + mystring;

    if(combined == "Hello" && DataAlreadyReceived == 0)
    {
      Serial.print("HiThere");
      DataAlreadyReceived=1; // so this indicates, that the data is already received
    }
  }

}

[camsysca]

As far as it goes, that might work. Certainly, UIMSO, there's nothing egregious. However, it ignores the context of a continuously looping, repetitive process. Is that relevant? In your application, will there be a single message, sent once, received once? If more than that is involved, then there's more work to be done.

[tolga121]

@camsysca

If more than that is involved, then there's more work to be done.

No, just a single message. The reason for this messaging, is:

each other should know, that they are there. So it's only one message being sent.

First, I wanted to send constantly a "Hello". (chosing the easy way of coding)

But now, I would never send constantly a Serial.print. And now I understand at least a little, how the Serial effect the ram itself... I know that there is still a lot to learn

Thanks to all of you @camsysca @Delta_G

[tolga121]

One think I wanted to say:

To be honest: I should know that large serial.print data have an effect on RAM. I sometimes forget to close the Serial Monitor on my Computer while the ESP is sending Serial.prints. And guess what ? My Computer is allways freezing because of the huge data printed on the serial monitor. So it absolutely effects the perfomance on any computer