xdata problem with ds5250?

now I am using ds5250 to do RSA algorithm.
I have 512k externel SRAM.
and the
off-chip code memory start:0x00000 size:0x40000
off-chip xdata memory start:0x0400 size:0x1000 start:0x40000 size:0x40000

the first xdata memory configuration is to do MAA.
but when compile,its xdata address space overflow.
and it seems that my second xdata memory is not used,it only uses my first xdata memory,and then xdata memory space overflow.
but if i do not config the first xdata memory,the RSA algorithm does not work.
who can help me?thanks

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