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Altera_Forum
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13 years ago

SRAM Addressing in QSYS

Hello I'm using a DE2-115 board with 2 MB SRAM (Address width 20. Data width 16).

I used Qsys "Generic tri state controller" to attach the memory to the NIOS processor.

Problem: How to access the entire 2MB RAM from c code ? Qsys give to the sram only a 20 bit address on its data bus (instead a 21 bit) so in C code I can access only the first MB.

The following example generates errors:

sram_mem= (void*)SSRAM_BASE;

memset(sram_mem,0,2097152);

Thanks

Tiziano

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    finally I foud the answare my self:

    set address width to 21 in generic tri state controller and detach the less significant bit (bit 0) from the sram addr bus.
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    --- Quote Start ---

    finally I foud the answare my self:

    set address width to 21 in generic tri state controller and detach the less significant bit (bit 0) from the sram addr bus.

    --- Quote End ---

    address width in generic tri state controller is the byte address arrange of SRAM, not the address bus width. Typically, SRAM has two bits byte-enable input, that's to say, the address bus width + log2(byte-enable width) is the address width of byte.

    Therefore, do not connect MLB of the address from generic tri state controller to any wire, let it free.
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Hey on your SRAM what did you do with the SRAM_UB_N and SRAM_LB_N pins? Also, did you have to modify any of the values in the module assignments section? For example memory size, memory units (which I don't understand what a memory unit is) etc...?