Regarding the register values for the SDRAM intialization.

[sivakumar]

Hi,

I am porting the northbridge 82845e for my motherboard. While coding raminit.inc file, I took the file from the 82830 chipset directory and modified as per the requirement of the 82845e chipset.
Now I want to know, How to get the register value of the regsiters, like DRB DRAM ROW BOUNDARY REGISTER and etc. 
Do I need to read these regsiter value from the system using normal BIOS? I could not find much details about the values in the specification.
Is my assumption is correct?

Thanks,
Siva

[Andrew Kohlsmith]

> I am porting the northbridge 82845e for my motherboard. While coding
> raminit.inc file, I took the file from the 82830 chipset directory and
> modified as per the requirement of the 82845e chipset. Now I want to know,
> How to get the register value of the regsiters, like DRB DRAM ROW BOUNDARY
> REGISTER and etc. Do I need to read these regsiter value from the system
> using normal BIOS? I could not find much details about the values in the
> specification. Is my assumption is correct?

At least on the 430tx, the DRB is programmed with the highest amount of memory 
in each row, in 4MB chunks.

In my particular case, I have one single 64M dual-sided SODIMM in Row 0.  So 
my DRB0 has a value of 0x10 (16*4 = 64) and DRB1-5 have the same value since 
they are not adding any memory.

Realistically you should be using a memory detection algorithm to try and find 
out how much memory is at each row and then programming the DRB registers 
correctly.  I have never done this, though.

Regards,
Andrew

[Ronald G. Minnich]

On Mon, 30 Dec 2002, sivakumar wrote:
> I am porting the northbridge 82845e for my motherboard. While coding
> raminit.inc file, I took the file from the 82830 chipset directory and
> modified as per the requirement of the 82845e chipset. Now I want to
> know, How to get the register value of the regsiters, like DRB DRAM ROW
> BOUNDARY REGISTER and etc.  Do I need to read these regsiter value from
> the system using normal BIOS? I could not find much details about the
> values in the specification. Is my assumption is correct?

now it gets hard. You need to understand how to read the SPD information 
and program these registers from SPD. Using BIOS settings is in most cases 
unnecessary, except for undocumented magic bits which are occasionally 
there.

Check out the code on e.g. the 440gx which reads SPD and programs the 
north bridge from this SPD data. That will give you an idea of how to 
proceed.

ron