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21375 external SDRAM access

Question asked by drmike on Mar 23, 2011
Latest reply on Mar 24, 2011 by drmike



In the SHARC Hardware manual for the 21375 it says:

"External memory address space is supported in normal word
addressing mode only. Single-instruction, multiple-data (SIMD),
extended-precision, short word, and long word addressing modes
are not supported."


When I have the external ram set up in the LDF using 16 bits:

seg_extsdram { TYPE(DM RAM) START(0x00200000) LENGTH(0x1ffff) WIDTH(16) }


everything works fine, I get 16 bit data on every short boundary as expected.  But when I try to go to 32 bits with this:

seg_ext32    { TYPE(DM RAM) START(0x00400000) LENGTH(0x1ffff) WIDTH(32) }

the compiler barfs giving me the error:

[Error el2011]  Invalid memory range and/or width for memory 'seg_ext32'


If short word access isn't supported, then how does short word access work correctly, and why can't I get the compiler to do the double read/write for 32 bit access?  What bit needs to be flipped to get normal word access to read/write SDRAM?