ESP32 NodeMCU: what value does node.heap() return when started?

Question

How much free RAM should there be after running the NodeMCU on the ESP32 ? That is, roughly what value should the node.heap() function return ?

Anonymous · Answer

. So really, I wouldn't suggest the result returned by this function. It's probably better to use node.egc.meminfo() .

TvWidget · Answer

I have a board with an Ethernet interface. If I don't start it then, as expected, I can create a string of up to 4kB in LUA code and perform various operations on it.
When the LAN starts up, trying to create a string over 2kB ends in a no memory error and a reset. If I perform some meaningless operation requiring memory allocation before starting the Ethernet, it manages to create longer strings later.
I am wondering where to look for the cause of the problem.

Anonymous · Answer

The most likely cause is in the garbage collector. You can experiment with its settings:

TvWidget · Answer

I have already experimented with this. I have not noticed any change.
The problem is not with a complex programme. I only have a few test instructions. The only thing that uses memory is Ethernet.
From the code in LUA, however, there is no control over this.

Anonymous · Answer

Which Ethernet module is it specifically? . As you have the lua interpreter loaded, the garbage collector is also automatically started.

TvWidget · Answer

. I don't really know what the question is specifically about. The PHY is on an IP101 chip.

Anonymous · Answer

Try calling the collectgarbage() function before running Ethernet.

TvWidget · Answer

I've done this before too.
At the start, the NodeMCU reports 85kB of free memory. When the Ethernet starts up, 45kB is left. I wonder if this starting amount is not too low. Perhaps the problem is at the compilation stage of the NodeMCU.

Anonymous · Answer

What values are returned by collectgarbage('count') before and after running the LAN?

TvWidget · Answer

Before launch 61.962890625
After launch 62.3232421875

Now I test run two instructions at the beginning:
eth.on(...
eth.ini(...
Then I try to create a long string and perform some operation on it. This ends with the message "not enough memory". However, the Esp32 does not perform a reset.
After deleting the first instruction, the error stops. Multiple long strings can be created. Perhaps this is a coincidence.

TvWidget · Answer

I don't think I quite understand how LUA works. I already know the reason for the low memory. I don't know if this is exactly the cause of the problem. However, after increasing it, the problem disappears.
I have the bootloader code added to the iNode MCU. It contains a short code in C, which always executes, and a relatively long code in LUA. The part in LUA is just a set of functions. They are not called during normal start-up. They do, however, occupy RAM. If I convert these functions into an object, will I save memory ?

Anonymous · Answer

. If the initialisation of the object of the class also happens later, that is allocating memory for that object. I don't know if you will save but you will move in time.

TvWidget · Answer

As I wrote earlier, I don't know how exactly the LUA interpreter works. Logically, all source code must first be rewritten into RAM. If this code is long it will take up more memory. Let's assume that an object is defined in this code. Later, during the execution phase of the instruction, if I substitute the value nil for this object, will the RAM allocated to the code be released ?

Anonymous · Answer

The Lua script is loaded into RAM from flash before execution. It takes up more RAM if the Lua source is plain text, as the Lua VM will have to compile it to bytecode. You can pre-compile Lua sources (already in ESP itself) using the command node.compile (). Additional savings in RAM usage can be achieved using node.stripdebug ().

TvWidget · Answer

The way I have mentioned now seems obvious to me. This is for me a very big advantage of the LUA language. As you wrote the script is loaded into RAM before execution. However, you can later remove any part of it from memory and reclaim the space. In other words, the program can dynamically load the necessary pieces of code and remove the unnecessary ones. E.g. after exiting the bootloder, I remove everything that was or could have been used in it.

TvWidget · Answer

. What does compiling the code do in practice ?

Anonymous · Answer

It is smaller in size, so it will also take up less RAM space.

TvWidget · Answer

The lc file is usually a bit longer than the lua file regardless of what I choose via node.stripdebug(). ESP seems to load this lc file entirely into RAM. So what is the mechanism for this memory saving ?

By the way, I have a question about the simultaneous use of two functionalities. It is about writing a file to flash memory and BT scanning. With me, sooner or later this triggers a reset without any error message. Should this be accepted ?

Anonymous · Answer

. It uses less memory on the heap. On the other hand, it's best to compile lua code for yourself on a PC and then load it into the ESP.

TvWidget · Answer

Suppose I put nil to an object containing a lot of lua code. If I display the result of the node.heap() function after some time, it is clear that the memory has been recovered. However, this does not happen immediately. So I tried executing collectgarbage(). However, this did not change anything. Is it blocking ? I.e. will the next lua instruction only execute once the garbage collection has been carried out ?

Anonymous · Answer

. Is it immediately after assigning nil to the object?

TvWidget · Answer

Yes

Anonymous · Answer

You could try setting a more aggressive egc behaviour: collectgarbage(setpause, 50). Set this at the beginning of the program, before the collectgarbage() calls.

kogiel · Answer

An old topic, but maybe someone will find it useful.
collectgarbage() on ESP does not work, whereas you can set the limit this way:
node.egc.setmode(node.egc.ON_MEM_LIMIT, -6144) -- Try to keep at least 6k heap available for non-Lua use

ESP32 NodeMCU: what value does node.heap() return when started?

What heap size should ESP32 NodeMCU report at startup, and what does node.heap() actually measure?

Topic summary

FAQ

Quick Facts

What value should node.heap() return right after a clean reset?

Why is node.heap() only a rough indicator?

How does collectgarbage('count') differ from node.heap()?

How much RAM does enabling Ethernet consume?

Why do >2 kB strings fail after Ethernet starts?

How can I immediately reclaim memory after using a Lua module?

Does collectgarbage() halt program execution?

How do I set an automatic low-heap trigger?

Does compiling Lua to .lc really save RAM?

What’s the safest way to pre-compile my scripts?

Why does writing to flash while Bluetooth scanning sometimes reset the ESP32?

What happens if heap drops below 6 kB?