dual port ram

Err I only have 3 registers that I must have a reset state for. This 
should fit well with what you have described. I am trying to code that 
up at the moment.

The point of this exercise is to get a cycle accurate operation for a 
register version and a dual port ram version. After that I will look at 
gate count and or speed.

The issues that I had with not being able to create small dual port rams 
was selft inflicted. I put the source code into the library when I 
didn't intend to.  OOps.

-- Andy

Jonathan Bromley wrote:
> On Sat, 28 Jul 2007 19:06:06 -0500, Ben Jackson <ben@ben.com> wrote:
> 
> 
>>On 2007-07-28, Jonathan Bromley wrote:
>>
>>>HOWEVER, you *can* initialise the contents of any Xilinx
>>>RAM at configuration
>>
>>But then you can't just 'reset' your design.  You have to
>>reconfigure from the bitstream to truly reset.
> 
> 
> Yes.  But the solution I offered - one "I have been written"
> register bit per RAM location - doesn't scale well; it's fine
> for up to a few dozen locations, no more.
> 
> If you can arrange that the RAM locations whose initial value
> matters to you are all in a small piece of address space, you
> can easily modify the "I have been written" trick so that
> it applies only to the small part of the memory that has the
> initialisation requirement.
> 
> More generally, it is not unreasonable to consider modifying
> your system's control state machine so that its first action
> after reset is to scribble the initialisation values into RAM,
> maybe by block-copy out of another memory configured as ROM
> with the reset values in it.
> 
> As Peter said, it's not practical to reset a big memory,
> and people have lived with this for ever.

On 2007-07-29, Jonathan Bromley <jonathan.bromley@MYCOMPANY.com> wrote:
> On Sat, 28 Jul 2007 19:06:06 -0500, Ben Jackson <ben@ben.com> wrote:
>
>>On 2007-07-28, Jonathan Bromley wrote:
>>> HOWEVER, you *can* initialise the contents of any Xilinx
>>> RAM at configuration
>>
>> But then you can't just 'reset' your design.  You have to
>> reconfigure from the bitstream to truly reset.
>
> As Peter said, it's not practical to reset a big memory,
> and people have lived with this for ever.

I just wanted the OP to realize the significant tradeoff he's making
by using preloaded blockrams.  If you 'reset' a design that uses them
you'll be surprised if you expected the reset values to appear in the
RAM again!

For something like a processor, I might just require a certain instruction
sequence at initialization that sets up the RAMs the way I want.  You'd
be in good company -- good luck executing anything on a modern Intel
processor without following 100 steps in a thick databook...

-- 
Ben Jackson AD7GD
<ben@ben.com>
http://www.ben.com/