SmartFusion2 SoC FPGA is distinguished by containing an embedded Non-Volatile-Memory (eNVM) that is used to store the code needed for the booting process of the FPGA after power up. So in the presence of this Flash memory why do we still need the eSRAM ?
eNVM is nonvolatile and has a limited number of write cycles.
eSRAM is volatile and has an effectively infinite number of write cycles. (Probably much faster, too.)
A typical application needs both kinds of memory.
eSRAM is likely a lot faster, and as it is SRAM it can be written an unlimited number of times. Think of the eNVM as the hard drive/SSD and the eSRAM as the RAM.