Enabling / Disabling I-Cache while Softdevice is Enabled on NRF52840

[donbosley]

NRF52840 - SDK 15.0 - SD 6.0.0

I'm trying to profile some code performance and I want to see how the I-Cache is impacting it.
If I attempt to access the NVMC register ICACHECNF once SD is enabled my device goes into a reset loop, crashing every time I try to turn off the I-CACHE.  Obviously a question of privilege once SD is enabled- so Is there a SD function/SVC call to "properly" enable/disable the I-Cache? Since SD engages it by default, I can't turn it off before I start SD.  

I also didn't see anything in the SDK_CONFIG.h with CACHE.

 

[Sigurd]

Hi,

donbosley said:

Since SD engages it by default, I can't turn it off before I start SD.  

I don't think that is correct. If you disable it before you enable the SD, the SD should not enable it again.

So just call this before ble_stack_init():

NRF_NVMC->ICACHECNF = 0x00;

[donbosley]

There are other posts that say it is, but I don't see it in the SD spec, so I'm not sure... I will try this and see what happens.

[peter9477]

I'm running with the S140 SoftDevice and the ICACHECNF value is 0x01.  Since I didn't enable it, and the default value in that register is 0, according to the datasheet, that must mean the SoftDevice enabled it.  That implies strongly that you can't disable it when running the SoftDevice, because it wouldn't know that you'd disabled it.... the state of the register would be identical to its value after a reset.

[Sigurd]

Hi peter9477,

This case is ~4 years old. Please create a new case for the issue you are having. Make sure to include SDK, SoftDevice version, etc when you create a new case:  https://devzone.nordicsemi.com/support/add  

[peter9477]

I have no issue. If you read my comment, you can see I'm responding to an earlier comment with what I believed was useful information that might help others who may come along later to read this thread...