about s3c2442

[Yi Qingliang]

On Thursday, January 10, 2013 10:14:07 AM Juergen Beisert wrote:
> Hi Yi,
> 
> Yi Qingliang wrote:
> > On Thursday, January 10, 2013 09:36:36 AM Juergen Beisert wrote:
> > > Yi Qingliang wrote:
> > > > 	I'm using barebox (based on mini2440) on my s3c2442 board,
> > > > 
> > > > 1. flash barebox into nand: can't start normally, but can see early
> > > > output on serial.
> > > > 2. load it in sdram: can start normally into shell, and then I use it
> > > > to boot kernel (also in sdram, also based on mini2440).
> > > > the kernel hang, no output.
> > > > 
> > > > after dig into it, I found something: add "mem=64M" into the kernel
> > > > paramer, then the kernel can start.
> > > > 
> > > > BUT:
> > > > the barebox doesn't pass that paramert to kernel for mini2440,
> > > > why the mini2440 kernel can start normally?
> > > > 
> > > > how does the kernel on 2440 get the sdram size?
> > > 
> > > There is no autodetection possible. Take a look into
> > > the "arch/arm/boards/friendlyarm-mini2440/lowlevel_init.S": This is the
I found it,
but:
md 0x48000028
48000028: 000000b2 (represents is 128)
it looks like the lowlevel_init is not executed, what's the problem.

> > > code which runs immediately after reset. It calls the
> > > function "s3c24x0_sdram_init" from the generic part, and uses hard coded
> > > values from "arch/arm/boards/friendlyarm-mini2440/config.h" to setup the
> > > SDRAM controller according to the attached SDRAM type.
> > > When the SDRAM is up and running, it is very easy to read back the SDRAM
> > > size from the SDRAM controller's registers (which is done in the
> > > function "s3c24xx_get_memory_size").
> > > 
> > > So you need routines which do the same job for your S3C2442 CPU.
> > 
> > and the kernel? how does the kernel know the sdram size for mini2440?
> > read the cpu register set by barebox?
> 
> No. The bootloader forwards this information to the kernel as an ATAG or via
> device tree. But this can only work, if also the bootloader knows the
> correct SDRAM size!
> 
> Regards,
> Juergen