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21375 external SDRAM access

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

Hello,

 

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?

 

Thanks.

Mike

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