Hi all,
I'm currently looking into an issue reported internally where the maximum latency for a zero-latency, priority 0 interrupt dramatically increases during a call to the PSA Protected Storage (PS) API. The maximum interrupt latency goes up ~10-fold, or even some more at times (it varies), and this is not acceptable to code running on the NS side for normal operation.
It's as simple as calling psa_ps_set(1, 4, buf, PSA_STORAGE_FLAG_NONE) once. During that call (which I am told was also seen to be unreasonably long: 600ms for 4 bytes, 1s for 1000 bytes), the maximum interrupt latency goes up. It (the maximum) seems to not vary too much even if increasing the size of stored assets (tested up to 4000 bytes), though it can get up to 20 times higher than the normal interrupt latency.
Also, other functions were tested (psa_generate_random(), psa_hash_compute()). Those don't provoke an increased interrupt latency. Maybe it's only about the PS, or maybe some other calls can provoke that as well.
Does someone have an explanation for that? And even more importantly, can that interrupt latency be reduced, ideally down to normal levels?
Thanks in advance. Tomi