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
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.
Interesting !! :)
Karthik Balaguru
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