Troubleshooting HFCLKSTARTED

[Adam Sillye]

Hi,

We created a custom board, with the nRF52 and the 32 MHz crystal oscillator according to the reference circuitry. We use ESB to communicate on RF, and it needs the HFCLK startup at the beginning like this code:

// start clock for RF RX/TX
static void rf_clock_start ()
{
	// Start HFCLK and wait for it to start.
	NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
	NRF_CLOCK->TASKS_HFCLKSTART = 1;
	while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
}

Our problem is the while loop is not terminating 9 out of 10 restarts, so EVENTS_HFCLKSTARTED never changes from 0.

This issue is not happening when using the PCA10040 dev board, and we also have an other custom board with the same type of crystal and capacitors (CX3225SB32DFFFCC, 2x 12 pF cap) which works well. So we assume that is hardware related..

Any tips what to check?

Thank you, Adam

PS. With this board, we have a DCDC regulator (but because of a design error) we don't have C10 in place. Is that possible that it relates to this problem?

[butch]

I don't have an answer and I'm not an expert, just thoughts: whether an oscillator starts reliably depends on adhering to a recommended layout. Are the layouts the same on your two boards? Can you characterize more than one board to have this problem? I don't think the DCDC is related, but can't you patch in the capacitor on your prototype and see if it helps?

[FormerMember]

As far as I understand, you have some custom boards where the HFCLK in most cases won't start, and some similar custom boards where the HFCLK starts without any problems? If that is the case, I would recommend you to check the soldering on the non-properly-working boards: Check that the crystal is well soldered and that it is mounted correctly (not shifted by 90 degrees for instance). In addition, you can replace the load capacitors (C1 and C2) by some new ones, just to make sure that they have the correct value.

[Adam Sillye]

Hi - thanks for the comments.

When we patched the C10 properly it immediately started to work.

So, C10 in DCDC is essential for HWCLK - at least on our board.

Thank you for the help.

[FormerMember]

Good that you made it work!