nrf5340 External high-speed clock source & Lowpower

RE: nrf5340 External high-speed clock source & Lowpower

zy_wen — Sat, 23 Nov 2024 04:56:03 GMT

Ok, thank you very much for your patience.

RE: nrf5340 External high-speed clock source & Lowpower

Vidar Berg — Fri, 22 Nov 2024 16:58:10 GMT

You typically don't need a high-accuracy clock source for serial interfaces such as QSPI, SPI, or TWI, as they use a shared clock. However, UART is asynchronous and relies on the clocks on both sides to not drift too far apart.

RE: nrf5340 External high-speed clock source & Lowpower

zy_wen — Fri, 22 Nov 2024 15:00:16 GMT

Another question, regarding the SDK modules you mentioned, when using LORA or QSPI flash, does the driver clock under it switch to the external high-speed clock?

RE: nrf5340 External high-speed clock source & Lowpower

Vidar Berg — Fri, 22 Nov 2024 14:51:43 GMT

It should be fine as long as the application does not release its request for HFXO while UART is enabled.

RE: nrf5340 External high-speed clock source & Lowpower

zy_wen — Fri, 22 Nov 2024 14:30:35 GMT

I use the CONFIG_PM_DEVICE_RUNTIME=y, pm_device_runtime_enable(uart_dev); to lower the power consumption of serial ports. It shouldn't be affected, right?

RE: nrf5340 External high-speed clock source & Lowpower

Vidar Berg — Fri, 22 Nov 2024 14:03:12 GMT

Hi,

Yes, the HFXO should be enabled when while UART is enabled. I have created a request internally that we should implement this in our UART examples. I posted a demo sample that does this here: RE: Suspending UART Async using PM_DEVICE ACTION_SUSPEND causes crash.

[quote user="zywen"]that all peripherals are currently using the high-speed external clock?[/quote]

Yes, correct.

RE: nrf5340 External high-speed clock source & Lowpower

Zion — Fri, 22 Nov 2024 12:45:41 GMT

So when I use the UART, do I need to enable the external high-speed clock in the application when needed and disable it when not? Does enabling the external high-speed crystal clock mean that all peripherals are currently using the high-speed external clock?

RE: nrf5340 External high-speed clock source & Lowpower

Vidar Berg — Fri, 22 Nov 2024 12:15:50 GMT

Hello,

The crystal oscillator is only active when requested by the application or one of the SDK modules. For example, the Bluetooth stack requests the crystal oscillator during protocol events but releases it afterward to allow the HF clock to shut down in sleep mode (System ON mode) to reduce the idle current. If you want to keep the crystal oscillator always on, you can request it using the onoff API as shown in this sample: https://github.com/nrfconnect/sdk-nrf/blob/ea2994fb4458302e5c3bb8404eabad28c1def943/samples/peripheral/radio_test/src/main.c#L18

Best regards,

Vidar