Re: [myhdl-list] Pre-Init RAM

[Martin S. <ha...@se...>]

Hi all,

> 
> Code exists to enable initial values but the difficult
> part has been making sure support is consistent across
> synthesis vendors (mainly FPGA).  Since we have not had
> someone willing to test all the vendors and verify the
> generic approach we have not been able to turn it on.
> 

This can be painful and cause support issues, so I wouldn't even start
thinking about adding it to MyHDL. I've taken an approach for the VHDL
side using generics as initialization value which works ok, but has some
minor quirks with various tools (some don't like an initialization of an
array with undefined size).

Example:

        constant BOOTROM_DATA_A_INIT : dram_bank_t := (
#include "dram_a_init.tmp"
        );

In the instanced memory block, the memory init data is passed on like

l1_ram_a : entity work.soc_memory_dma
        generic map (
     		...
                DRAM_INIT  => BOOTROM_DATA_A_INIT
        )


As you can guess, there is some abuse of the cpp involved, also, there
are switches to satisfy the tools.
Another tool generates the actual memory data content. It gets much more
complicated when using non standard bit widths (like 18 bit CPU
instructions).

There is so much case dependency, that it might be very hard to satisfy
everyone. I'd rather see if we can collect a few use cases and tricks
from the community and document them.

Greetings,

- Martin