How to always run the CPU at full speed?

[jaeheung]

Hi,

I am developing a product using nRF52833. (S113, SDK 16, IAR8)

I am developing based on the usbd_ble_uart sample.

I use ble, spi, twi, ppi, saadc.

and, I use external 32Mhz crystal and external 32.758kHz crystal

I don't care about power consumption.
Operating as fast as possible is a top priority.
So I want to always run the CPU at 64Mhz without going into sleep mode.

How is it?

[Jørgen Holmefjord]

Hi,

The CPU will always run at full speed (64 MHz) when it is active. Just avoid putting the CPU in sleep (__WFE(), sd_app_evt_wait(), etc) if you do not want wakeup times. It is not a lot to gain, device startup in constant latency mode is 3 us, but if current consumption is not an issue, there should be no problems leaving the CPU running.

Best regards,
Jørgen

[jaeheung]

Thanks..

I did another test with respect to cpu speed.
I tried running the code below using the saadc sample code.

---------------------------------------------

while (1)
{
   nrf_gpio_pin_clear(25);
   nrf_gpio_pin_set(25);

}

------------------------------------------------

Looking at the gpio output with an oscilloscope, a signal of about 1.3Mhz comes out.
Is this correct?
If the CPU is running at 64Mhz, isn't it supposed to output gpio faster?

[Jørgen Holmefjord]

It may very well be correct. It depends on what assembly-instructions that code is compiled into. The cycle count for each assembly instruction is given in the ARM Cortex-M4 documentation.

Also, note that the HW peripherals run off a 16 MHz peripheral clock. See this post for more details.

[jaeheung]

Thanks.