change clock speed nrf52

RE: change clock speed nrf52

TY — Tue, 12 Jul 2016 10:59:33 GMT

Great that explains what I am experiencing.

Since I am sure now that the nRF52 is running on full speed. I can focus on making my code faster in order to handle the interrupts.

RE: change clock speed nrf52

RK — Tue, 12 Jul 2016 10:38:55 GMT

ok so 500kHz, that's the time for a full cycle so you're getting one toggle every 1us, so that's closer. With the clock running at 64MHz that's about 64 instructions per toggle. I just eyeballed the compiled code and rough-counted the instructions as something like 32, that includes all the entry/exit code for the routine as well as the actual toggle.

So if my count's right, we're about a factor of 2 off. But you're running from flash, that might introduce a wait state. I'm not convinced by that statement partly because there's cache RAM on the chip to deal with that exact thing. That simple code should prime the cache and get it running with 0 wait states. If you have however an average of 1 wait state, there's your factor of two.

Hmm .. checks manual. I think the cache isn't enabled by default. Try that one thing, NRF_NVMC->ICACHECNF = 0x01. See what happens.

RE: change clock speed nrf52

TY — Tue, 12 Jul 2016 09:54:59 GMT

This all my code: err_code = nrf_drv_clock_init(); APP_ERROR_CHECK(err_code);

while(1)
{
	nrf_gpio_pin_toggle(LED_4);
}

And I am measuring the frequency with an Tektronix oscilloscope. I had on button poll left which I have deleted now and now I am getting close to 500 Khz.

The gcc optimaziation is off, how can I see the instructions count.

RE: change clock speed nrf52

RK — Tue, 12 Jul 2016 09:25:49 GMT

You can't change the system clock, it's 64MHz and that's it.

How are you measuring 300kHz on the LED pin? I just compiled nrf_gpio_pin_toggle() and counted the instructions and it's about 30, call it 32, so if all you have is that in a loop there's no way you can be getting 300kHz, should be 6 times that, that is really all your code,

while(1)
    nrf_gpio_pin_toggle( LED_4);