Timer jumps after 35 minutes on K64F

[marcuschangarm]

When running the following program on a K64F, the timer value jumps drastically after 35 minutes.

#include "mbed.h"
#include "rtos.h"

Timer tick;

int main()
{
    tick.start();

    for(;;)
    {
        printf("%lu\r\n", tick.read_ms());
        wait(1);
    }
}

Output after 35 minutes:

2144601
2145608
2146615
4292819952
4292820963
4292821973

[0xc0170]

I would like to test this on earlier revision (mbed lib <120) when we used KSDK 1.0

cc @mmahadevan108

[mmahadevan108]

Hi Martin, Does this exist on the earlier version as well?

[0xc0170]

@marcuschangarm What version of mbed are u running? SHA? Can u test the older version with KSDK?

[marcuschangarm]

I'm on #974ecf731c8a5de78acc9e40573f2a7c7641c2cd.

What version do you want me to test?

[0xc0170]

@marcuschangarm 868ca35 (use mbed lib 119) please and let us know

[marcuschangarm]

Same result on mbed 119 and mbed-rtos 108:

2144600
2145608
2146615
4292819952
4292820963
4292821973

[svastm]

It's an integer overflow error. 2 146 615 ms mean 2 146 615 000 us which is just a little bit under the max integer (32bit) value. We could add one of this behavior to handle this type of overflow:

• reset the timer
• return an overflow error code

If you need a clock you can use the rtc (if your device has one).

[marcuschangarm]

@svastm thank you for the explanation.

I'm a bit surprised the Timer API uses signed values for measuring time.

In this particular case I would have expected the timer to reset on an overflow.

[ciarmcom]

ARM Internal Ref: IOTMORF-172

[pan-]

@0xc0170 Any update on this ?
It is an API defect affecting all targets and every release of mbed-os.
What should be done ?

[marcuschangarm]

As a user, I would expect that:

• reading a timer would return an unsigned value.
• I could register a callback function to receive overflow callbacks.
• a function called read_ms would have increased range as opposed to read_us, i.e., read_us should overflow 1000 times before read_ms would.

[pan-]

I could register a callback function to receive overflow callbacks.

What is the purpose ? If an overflow occur, the user won't see it until its overflow callback is called. During this time, the timer can be read and the overflow won't be handled.

Checking overflow before (or after) the timer read induce the same kind of issue. Again, there is a small window of time between the timer read operation and the overflow check which can cause an improper handling of an overflow.