Hi @MithileshKumar ,
Thank you for your interest in the NXP MIMXRT product, I would like to provide service for you.
If you have the bootloader, I highly recommend you do the flexRAM allocate in the bootloader directly, as you know, the code will run the bootloader at first.
Anyway, when do the flexRAM allocation, it can use the register to modify it. So, normally, after reset, it enters the reset handler, do the related register confiruation.
I suggest you do the flexRAM allocation in the bootloader which is running in the flash, then to the app, you can use your allocated memory assignment directly.
If you still have issues, I think, you even can use a simple project, eg, led_blinky, with your DTCM i.e. 256k, and ITCM - 128k, OCM - 128k. test it at first, after it works, then meger your flashloader again.
Wish it helps you!
If you still have questions about it, please kindly let me know.
Best Regards,
Kerry