Is external crystal neccessary at all on 52832

RE: Is external crystal neccessary at all on 52832

Roland — Wed, 04 Oct 2017 07:21:54 GMT

Thank you @Sigurd, that's perfect.

RE: Is external crystal neccessary at all on 52832

Sigurd — Tue, 03 Oct 2017 07:26:46 GMT

When using the internal RC oscillator, the SoftDevice will calibrate the RC oscillator using the HF 32MHz crystal. The recommended configuration for NRF_CLOCK_LF_SRC_RC on nRF52 is rc_ctiv=16 and rc_temp_ctiv=2. This will ensure calibration at least once every 8 seconds and for temperature changes of 0.5 degrees Celsius every 4 seconds. The recommended operating temperature for the nRF52832 is between -40 to +85 degrees Celsius, so -20 degrees should not be a problem for the nRF52832.

RE: Is external crystal neccessary at all on 52832

Roland — Tue, 03 Oct 2017 03:34:00 GMT

@Sigurd thank you. One further concern is, as it an industrial application, how is the internal RC behaving under large temperature fluctuation, like -20degree in winter? Do i need to use different calibration parameters?

RE: Is external crystal neccessary at all on 52832

Sigurd — Mon, 02 Oct 2017 09:07:00 GMT

Hi,

The run current for the 32.768 kHz crystal oscillator is 0.25 µA, while the run current for the 32.768 kHz RC oscillator is 0.6 µA. Except for this there is no "performance degrade". You save some cost and PCB space by using internal RC, but it uses a bit more power.

RE: Is external crystal neccessary at all on 52832

Roland — Sat, 30 Sep 2017 14:17:26 GMT

@Sigurd,

Turns out that 32M xtal is faulty. Replace with the part number in official BOM resolve the problem. thanks for the support.

Compared with using external LF, will there be any performance degrade if i stick to use the internal LF RC with BLE activities? and by how much? is that some figure can be quantifiable？

RE: Is external crystal neccessary at all on 52832

Roland — Fri, 29 Sep 2017 15:19:57 GMT

@Sigurd,

thanks for the answer. That explains the problem. I did not see waveform of 32M xtal on oscilloscope so there must be some problems about it. I will test more and let you know.

RE: Is external crystal neccessary at all on 52832

Sigurd — Fri, 29 Sep 2017 12:27:45 GMT

Do you have a oscilloscope that can measure 32 MHz ?

You can try to call sd_clock_hfclk_request(), and then call sd_clock_hfclk_is_running. sd_clock_hfclk_is_running() returns 1 if the external crystal oscillator is running.

You could e.g. try something like this:

sd_clock_hfclk_request();
uint32_t flag = 0;
// Enter main loop.
for (;;)
{
    if (NRF_LOG_PROCESS() == false)
    {
        power_manage();
    }
    sd_clock_hfclk_is_running(&flag);
    NRF_LOG_INFO("Flag: %d", flag);
}

If you dont't get "Flag: 1", then you have a problem with the HF crystal. And you should then double check that the crystal on your board is mounted correctly, i.e. not shifted by 90 degrees for example.

Yes, the ble_advertising_start() will return 0, and bsp will start blinking even if the HF crystal is not mounted. The SoftDevice will wait for the HF crystal to startup before you see any BLE activity.

Attach a debugger, and use e.g. J-Link RTT viewer to see the nrf_log's

Let me know how it goes!

RE: Is external crystal neccessary at all on 52832

Roland — Fri, 29 Sep 2017 07:44:59 GMT

@Sigurd,

YES, i have changed the LF src to NRF_CLOCK_LF_SRC_RC. I used 16 for NRF_SDH_CLOCK_LF_RC_CTIV, i will try 32 again.

More facts from my testing:

As the application now does not need external LF xtal so i can actually compare the results that same application running on my custom board and the 52DK. on 52DK the application seems all working, as i can discover my services on central side. But just not on custom board.
I can not measure 32MHz waveform on my custom board's HF xtal, so apparently it does not work for some reason(though i am not sure for now). But a question is if HF xtal not working is it possible that ble_advertising_start() returned err_code 0? And i can see LED blinking tells that bsp indicator is working.

RE: Is external crystal neccessary at all on 52832

Sigurd — Fri, 29 Sep 2017 07:21:31 GMT

Did you set the SoftDevice clock source in sdk_config.h to NRF_CLOCK_LF_SRC_RC ?

You should also set the NRF_SDH_CLOCK_LF_RC_CTIV to 32, and the NRF_SDH_CLOCK_LF_RC_TEMP_CTIV to 2.

RE: Is external crystal neccessary at all on 52832

Roland — Thu, 28 Sep 2017 16:33:03 GMT

thanks @Sigurd and @RK for the clarifications. I may misunderstood some posts.

My custom board of 52 already made, with an external HF 32M xtal, no LF though. So i think the only way now is to use internal RC osc for SD then. So am i correct to set NRF_SDH_CLOCK_LF_XTAL_ACCURACY in sdk_config.h to NRF_CLOCK_LF_XTAL_ACCURACY_250_PPM ?

I am asking because though seems that i already made the application running on my custom board, and the advertising started (returned error code 0), but i can not find my device on central side. did not find any clue yet.

RE: Is external crystal neccessary at all on 52832

RK — Thu, 28 Sep 2017 07:38:43 GMT

Your 1) is incorrect. What is not recommended is using the HF clock to synthesize the LF clock.

RE: Is external crystal neccessary at all on 52832

Sigurd — Thu, 28 Sep 2017 07:25:54 GMT

Hi,

External HF crystal is mandatory if you want to use the radio peripheral. If you are using BLE, you have to use an external 32 MHz crystal with a frequency tolerance of max 40 ppm. As mentioned in this post:

The external HF clock is critical for data timing and more critical to keep the bluetooth radio on the correct frequency. All the 2.4GHz channels are derived from the 32MHz crystal. So the ppm accuracy of the xtal will be the same ppm accuracy of your carrier in the 2.4GHz band.

2 .

External LF crystal(32 kHz)is not mandatory, but recommend. See this and this post.

Since you are migrating to nRF52832, I recommend to take a look at the General PCB design guidelines for nRF52 series tutorial