Linux RAM driver question

Does embedded system require RAM driver , does we select it when build
kernel ?

When does it load , by boot loader or system Image , where is its
Linux source folder ?

Why a PC Windows do not require RAM driver ?

Thank for your teaching .

On Mon, 25 Feb 2008 01:43:26 -0800, Kid wrote:

> Does embedded system require RAM driver , does we select it when build
> kernel ?
> 
> When does it load , by boot loader or system Image , where is its Linux
> source folder ?
> 
> Why a PC Windows do not require RAM driver ?
> 
> Thank for your teaching .

RAM is so integral to the operation of a system that any RAM interface 
logic will be implemented in hardware.  Dynamic RAM needs to have special 
driver hardware, which may need to be set up by the processor when the 
system comes out of reset, but this must be done before the processor 
starts operating out of RAM so in a PC it would be handled by the BIOS.

Now, I _don't_ know if PC chipsets need to have their RAM drivers set up 
by the processor or if they're just designed to work with specific types 
of RAM and that's that.  I know the Motorola MPC860 did work with a 
bazillion different types of RAM, and the very first thing that the 
startup code did was to configure the chip's DRAM driver -- in fact, the 
assembly portion of the startup code that we used did little more than 
set up the DRAM driver, set up the memory manager, set up the stack 
frame, then jump to C.

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

On Feb 25, 9:58 am, Tim Wescott <t...@seemywebsite.com> wrote:

> Now, I _don't_ know if PC chipsets need to have their RAM drivers set up
> by the processor or if they're just designed to work with specific types
> of RAM and that's that.  I know the Motorola MPC860 did work with a

They certainly do need power-on setup. RAM modules have I2C EEPROMs on
them so the host can read out their timing parameters and set up the
SDRAM controller accordingly. The controllers even need to have PCB-
layout-specific timing correction values poked into them to allow for
the different trace lengths to different data bus pins of the RAM
modules. Tuning a fast SDRAM controller in a PC design (or a similar
high-end design like Cell) is a _REAL_ specialized and exhausting job.

On Feb 26, 3:53=A0pm, larwe <zwsdot...@gmail.com> wrote:
> On Feb 25, 9:58 am, Tim Wescott <t...@seemywebsite.com> wrote:
>
> > Now, I _don't_ know if PC chipsets need to have their RAM drivers set up=

> > by the processor or if they're just designed to work with specific types=

> > of RAM and that's that. =A0I know the Motorola MPC860 did work with a
>
> They certainly do need power-on setup. RAM modules have I2C EEPROMs on
> them so the host can read out their timing parameters and set up the
> SDRAM controller accordingly.

Interesting !! :)

> The controllers even need to have PCB-
> layout-specific timing correction values poked into them to allow for
> the different trace lengths to different data bus pins of the RAM
> modules. Tuning a fast SDRAM controller in a PC design (or a similar
> high-end design like Cell) is a _REAL_ specialized and exhausting job.

Karthik Balaguru