ESP32 Forum

I have problems when accessing the same variable. I tried declaring an integer as volatile and then non volatile and the behaviour is not consistent. Sometimes volatile helps to get the right value, sometimes not. Also sometimes accessing a volatile variable affects accessing real values in non volatile vars, for example I have

volatile int Mode;
int test;

If I do something like

Mode=1;
if (Mode) Serial.println ("Test : "+String(test));

will have different result (if other core is writing to a variable "test" at the same time) then just

Serial.println ("Test : "+String(test));


Although the result should be the same. I did objdump and found that assembler instruction memw is executed when accessing a volatile var, which does "Order memory accesses before with memory access after". i.e. something like update values in cache from the memory.

My question is: are there some quidelines on how to manage data access from two cores?

Can you post your entire project?

That's around 200 kB of code already (391713 bytes of program storage space), so I don't think it's a good idea
Anyway, I figured it out. I only use volatile variables when the change is needed to be noticed promptly by another core. For other types of variables non volatile is fast enough.

hi
volatile variables do not protect variables from date races
esp idf provides two possible protection options depending on application requirements
mutex and spinlock

Although the result should be the same.

This is a common misconception about what volatile does and does not do, especially when it comes to the interactions between volatile and non-volatile accesses.
A 'clean and simple' approach using locks/mutexes instead of volatile variables is more promising.