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Altera_Forum
Honored Contributor I
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What is VHDL equivalent for Verilog $readmemb to initilze RAM/ROM?

The $readmemb() is mentioned in "Recommended Coding Styles" page 12-26. It seems that this can be used in simulation AND synthesis.  

 

If one unfortunately uses VHDL rather than Verilog, than how does one initialize the RAM/ROM? The idea is to write code such that it gets inferred as the correct type of memory block AND be initilized usign the required content from a MIF file. In other words, it must synthesize.
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Altera_Forum
Honored Contributor I
471 Views

Unfortunately, Altera has decided not to support what would be the most obvious replacement - the textio package (Xilinx Supports it). 

That means the only ways to support mem init in synthesis are: 

1. Use a constant and initialise the ram signal in the code: 

 

signal my_ram_sig : my_ram_type := MEM_INIT_CONSTANT; 

 

2. Use a mem init function: 

 

function mem_init_function return ram_t is variable ret : ram_t; begin for i in ret'range loop ret(i) := --some calculated value! end loop; return ret; end function; signal my_ram_sig : my_ram_type := mem_init_function;  

 

3. Use attributes as an init to the ram (either in code or via project assignments) 

 

type mem_t is array(0 to 255) of unsigned(7 downto 0); signal ram : mem_t; attribute ram_init_file : string; attribute ram_init_file of ram : signal is "my_init_file.mif";  

 

The only issue with 3. is that it wont initialise in simulation. 

 

For simulation of method three, you could write a function to read the mif file to init the contents.
Altera_Forum
Honored Contributor I
471 Views

You are implying that I write a package that is automatically generated from a differnet programming language, this package shall contain the memory initialization function with the raw data.

Altera_Forum
Honored Contributor I
471 Views

No, that would seem a little overkill. How do you need to initialise the ram? do you already have a .mif file? Could you just generate the data easily with a function? Why do you really need to initialise it at all? 

 

If you use the altsyncram component, you can specify a .mif file to use, and it will work in both simulation and synthesis.
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