Go Down

Topic: nanos() [time elapsed since program start in nanoseconds]? (Read 4039 times) previous topic - next topic


Nov 27, 2013, 12:46 am Last Edit: Nov 27, 2013, 05:03 am by titous Reason: 1
hi everyone!

In my current application I'd like to be able to have access to timing in the 10 to 100 ns range.  So I started digging around in the micros() source code and came up with the following:

Code: [Select]
uint32_t nanos( void )
    uint32_t ticks ;
    uint32_t count ;

    do {
        ticks = SysTick->VAL;
    } while (SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk);

    // GetTickCount() is millis()
    uint32_t load= (SysTick->LOAD + 1 - ticks);
    uint32_t milliS = GetTickCount() * 1000000;
    uint32_t microS =  load/ (SystemCoreClock/1000000) * 1000;
    uint32_t nanoS = load/ (SystemCoreClock/10000000); // these are actually 100s of nanoseconds; 84MHz  = 11.9ns
    //Serial.print(milliS); Serial.print(" "); Serial.print(microS); Serial.print(" "); Serial.println(nanoS);
    return milliS + microS + nanoS;


It's exactly the micros() source code except that on the return I changed the divisions by 1000.  Could someone please comment on whether this is the right approach?

On a side note: isn't division notoriously slow on the Due, so isn't there a better way to optimize this code for performance?


multiplication and division are in hardware on the Cortex, multiplication is single cycle,
don't know the figure for division though.
[ I won't respond to messages, use the forum please ]

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131