nrf_cc310 and ARM TrustZone CryptoCell in interrupt mode

[StefanHri]

Does the nrf_cc310 support interrupt operation? I want to start the calculation of a hash/asymmetric signature but don't want that the CPU busy-waits until the calculation is complete? I cannot find an example for that in /examples/crypto/nrf_cc310/.

[Einar Thorsrud]

Hi,

The CC310 runtime library use interrupts internally, but the API calls are still blocking. This is achieved by the library calling __WFE() internally when waiting for events. During this time the CPU can sleep or other interrupts can be serviced. There is also some use of busy-waits in a few special cases, but only for very short waits.

[TSonono]

During this time the CPU can sleep or other interrupts can be serviced. There is also some use of busy-waits in a few special cases, but only for very short waits.

I'm curious to what extent the CPU goes to sleep when using the CC310. I've been monitoring NRF_PWR_MGMT_SLEEP_DEBUG_PIN and can't see the MCU ever enter sleep mode when using the CC310. We use the CC310 for ecdh and eddsa (we are not using the nrf crypto backend/frontend). Should I open a separate issue for this or is this the expected behavior?

This was on SDK v17.0.2

Regards,

Tofik

[Einar Thorsrud]

Hi Tofik,

The CC310 library calls WFE() internally, so the power management function is not called even though the CPU sleeps in this case. Therefor you cannot rely on the sleep debug pin in this specific case. This is different from other SDK libraries, so I understand the confusion.

Einar

[TSonono]

I see!

Thanks Einar!