[ts-7000] Re: help in loading linux kernel from sdcard.

["pritam" <>]

Thanks Breton,

I got my fat 16 file system code working now. In this code i copy Zimage, 
ramdisk and kernel assembly setup code and finally jump to kernel assembly 
setup code. But nothing is happing. The kernel is not booting. 

On my board i have 64Mb sdram and its connected to sdcs3. I used redboot to 
load the kernel and see what all parameters are being passed. 

Redboot shows
RAM: 0x00000000-0x04000000, 0x00041f68-0x03fbd000 available

So i copy 

#define RAMDISK_LOAD_ADDRESS     0x01000000 
#define RAMDISK_LOAD_ADDRESS_END 0x01800000 

#define KERNEL_LOAD_ADDRESS      0x03000000 
#define KERNEL_LOAD_ADDRESS_END  0x03800000 
                                     
#define KRNLSTARTUP_LOAD_ADDRESS 0x00010000 //kernel asmbly stup code

So i modified your code to copy the kernel at 0x03000000, Ramdisk remains the 
same.

In your atags list you have mentioned set the memory as 4 banks.

I modified that as follows:   
---------------------------------------------------------------------
linux_start:
        @ copy atags to 0x0000 1000     @ a location where they won't be trashed
        mov     r1, #0x01
        lsl     r1, #8                  @ target address to r1
        adr     r2, atags
        adr     r3, atags_fin           @ fetch addresses
1:      ldr     r0, [r2]                @ fetch address from r2
        str     r0, [r1]                @ write word
        add     r1, #4
        add     r2, #4
        cmp     r2, r3
        bne     1b

        mov     r2, #0x01
        lsl     r2, #8                  @ 0x100 to r2 (atags pointer)

        mov     r1, #0x25
        lsl     r1, #4
        add     r1, #0xf                @ 607 machine id (25f hex)

        mov     r0, #0                  @ clear r0

        mov     r3, #03                 @ target address in r3
        lsl     r3, #24                 @ 0x0300 0000
        bx      r3                      @ branch to address 0 - start linux




        .align 4
atags:          .word   5
                .word   ATAG_CORE
                .word   0               @flags
                .word   4096            @pagesize
                .word   0               @rootdev - unknown...

                .word   4               @ size of memory tag
                .word   ATAG_MEM
                .word   0x03F7B098      @ size
                .word   0x00041f68      @ start

                .word   4
                .word   ATAG_INITRD2    @ second rev, physical mapped initrd 
                .word   0x01000000      @ start in second physical page
initrd_size:    .word   0x00000000      @ filled in by loader!

cmdln_start:    .word   (cmdln_fin-cmdln_start)/4
                .word   ATAG_CMDLINE
                .asciz  "console=ttyAM0,57600 root=/dev/ram" 
                .align  4
cmdln_fin:      .word   0               @ buggy terminator criterion in setup.h
                .word   ATAG_NONE


                .word   0x00000000
atags_fin:      .word   0x00000000
---------------------------------------------------------------------


I compiled this code using thumb mode and used a linker script to link it. 
---------------------------------------------------------------------
SECTIONS 
 {
 . = 0x00010000;
 rom :  { 
        *(.text) 
        *(.rodata) 
        *(.rodata.*)
        *(.got)
        *(.got.*)
        *(.data.rel.ro)
        }
 ram :  { 
        *(.bss)
        *(COMMON)
        }
 }
---------------------------------------------------------------------

I am new to arm assembly, hence not sure if the address used in linker script 
affects the location from where this code is executed once it is copied in the 
memory. 

I even tried to reading back the data from kernel load address and ramdisk load 
address. The data is fine 

It will be a great help if you can please share your comments on this.

Thanks
Tama




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