timerReadMicros returns older value

[ummarbhutta]

Hardware:

Board: ESP32 Dev Module
IDE name: Arduino IDE
Upload Speed: 115200
Computer OS: Windows 10

Description:

I am working on an application where I have GPIO interrupt defined, and on each interrupt I want to record timer value for which I am calling timerReadMicros but the problem I am facing is timerReadMicros always return older time when it was last called, and if I call it second time it seems to be close to real value. It looks like timerReadMicros is storing and returning older values. I have tried timerRead , timerReadSeconds . Every function have same behavior. Following is the code snippet

void IRAM_ATTR entry_isr()
{
    value = timerReadMicros(timer); // will always return value it was called the last time
}

if I change the code like this

void IRAM_ATTR entry_isr()
{
    timerReadMicros(timer); // will always return value it was called the last time
    value = timerReadMicros(timer); // kind of hack to get correct value
}

timer configuration is like this

  timer = timerBegin(0,40,true); //Input clock 80MHz, Prescaler = 40, Upward counting ==> 0.5microsecond per counter increment
  timerWrite(timer, 0); //reset timer to 0

I assume I am missing something very basic here.

Any help is really appreciated.

[atanisoft]

duplicate of #3434. There needs to be a small delay inside timerRead(), you can try delayMicroseconds(1); instead of delay(1); which was mentioned in the other issue (a 1ms delay inside the ISR WILL cause problems).

[atanisoft]

also if you just need an incremental timestamp you can call esp_timer_get_time(); which will return the number of microseconds since boot.

[ummarbhutta]

Hi @atanisoft, I wouldn't go for updating the library code and adding delay after update. Not sure why a delay is required, isn't it preventing us from full control on hardware timers? e.g. If I am using timerRead with scaling less than 80 than I can get resolution of less than 1 microseconds.. But putting delay will make it hard.

Anyways thanks for second suggestion, for now I read resolution in microseconds so will give it a try.

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