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Zephyr: Slow Flash write seen on STM32H747i-disco board when using M4

Associate II

Hello experts,

I have a requirement to use M4 to write to flash partitions under Zephyr OS. Currently Flash controller driver doesn't support M4. So I have a pull request being reviewed here

What I have observed is that flash write is really slow taking about 6 minutes to erase and write 256KiB partition. I have sample application for this as part of the PR.  I have seen erase happens fast, but read/write is slow, where as on M7 it is pretty fast about 3 seconds. I have discussed this in the zephyr PR discussion but so far no one could answer if it is expected or not. I believe ART Accelerator is present in the SoC used in this board. Another observation is that internally we are using STM32H755 for our work and we don't see the same behavior. On this SoC, flash write is as fast as in M7 even though ART Accelerator is enabled in both cases at