i.MX6 RTC_XTAL bumps

[m_c]

In IMX6DQRM Revision 2, 71.1 it said Automatically switch to the external oscillation source when sensed on the RTC_XTAL bumps(contacts) (32 kHz specific feature). Is it means i.MX6 sensed it by checking XTALOSC_RTC_XTALI & XTALOSC_RTC_XTALO pin contact with external oscillator or not?

[gusarambula · Accepted solution]

You are correct. In case the i.MX6 detects that an external oscillator has been connected to the XTALOSC_RTC_XTALI & XTALOSC_RTC_XTALO pins this external oscillator is used. In the absence of an external RTC oscillator the i.MX6 switches to the internal ring oscillator.

More details on this on-chip oscillator can be found on Section 4.1.4 of the i.MX6DQ Datasheet. I recommend reviewing these as the on-chip oscillator is not as precise as a 32 kHz crystal.

[chenjasper]

So, if an external RTC oscillator is not use, the i.MX6 will switches to the internal ring oscillator, but when I didn't use an external RTC, few boards sometime will not boot and reboot, it just stop and cannot see message from UART debug port. I assert POR signal, iMX6 still not work.

But when I connect RTC_XTALI with 4.7k to ground, the symptom was never happen again. Is it any problem with software or hardware setting?

[gusarambula]

Hello Chen Jasper,

This is normal HW behavior. In order to engage the internal on-chip loose-tolerance ring oscillator you need to tie RTC_XTALI to GND and leave RTC_XTALO floated.