nRF52840 QSPI XIP and standby

[changjo]

I have been investigating the possibility of using the QSPI external flash peripheral on our NRF chip. After doing a typical qspi read command, the external flash chip would go back to standby mode which uses about 85uA. After doing a xip_function, which looks like a typical read command with a continuous read commands depending on the function, the external flash chip would not go back to standby. This results in 2.3 mA idle draw. The QSPI XIP is functioning but I am wondering why the flash does not go in standby after the XIP operation. I want to know if there is any way to save power while or between using XIP. Is there a way to modify software to ensure standby mode is done after any qspi operation? 

Here is my configuration:

nRF52840, using Macronix MX25L12835F QSPI NOR flash,

Running with SDK14.0, using QSPI library. Dual SPI with mode 0, PP, READ2IO, 32Mhz. 

[run_ar]

Did you implemented the workaround mentioned in anomaly 122?

[changjo]

I have tested out the workaround but this does not fix the issue I have. The anomaly 122 workaround is for un-initializing the qspi chip. Whereas the situation I am referring is in between xip operations, I would like the qspi chip to go into standby.

[run_ar]

The best solution would be to uninit QSPI when it is not in use. You could also test deep power down mode http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52840.ps/qspi.html?cp=2_0_0_5_18_6#deep_power_mode. In addition you should check that CS is deselected.

 

 

[changjo]

For the application, the execute in place may be used for indeterminate amount of time depending on how much code will be off loaded. Therefore knowing when to uninit or put deep power down mode will be difficult. Also to put deep sleep or uninit in every location would be quite a task. If there was a work around that the QSPI can self managed is something more preferable.