You will need to exercise care. SRAM (called isram in the linker scripts) is already used for other things including the MMU page table: https://github.com/patacongo/incubator-nuttx/blob/master/boards/arm/sama5/sama5d2-xult/scripts/dramboot.ld#L21I will, I believe, need to declare - place - MCAN related structures such that they (or at least some elements of them) are in SRAM.
The first 112Kb should be available, however, unless the board logic uses that too.
