SDRAM byte (8-bit) write access

Hi all,

I've a NiosII system based on EP1C6144, with an extrernal 2Mb 16-bit wide SDRAM.

While writing SDRAM with 16 or 32-bit wide data gives the expected result, if I try to write a single byte (8-bit) I find 2 adiacent bytes written in SDRAM with the same value.

To check this behaviour I wrote a simple in-line assembler that make me sure I have not compiling problems:

   __asm__  ("nop \n\t"
                    "movi r6, 0x12 \n\t");                         // Loads data to be written (0x12) in register R6
              
   __asm__  ("movhi r7, %hi(0x1F7F84) \n\t"
                    "ori r7, r7, %lo(0x1F7F84) \n\t");       // Loads address data has to be written to (0x1F7F84) in register R7
 
   __asm__  ("stb r6, 0(r7) \n\t");                           // Writes BYTE in R6 in address pointed by R7+0
  

Before these instructions I have the memory window displaying

  0x001F7F84    0x00 0x00 0x....

and after instructions...

  0x001F7F84    0x12 0x12 0x....

I checked all SDRAM's timing parameters and they seems to be right, in effect code runs from SDRAM and 16 and 32-bit accesses are correct, and also any read access.

Any idea?

Thanks all,

Paolo