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List:       uclinux-dev
Subject:    [uClinux-dev] HOW-TO compile linux to run directly from flash?
From:       "Lars Holowko" <Lars.Holowko () lantronix ! com>
Date:       2009-04-13 21:57:35
Message-ID: 022254FBC8645942BBF88A022862CDD33C5FFC () 3putt ! int ! lantronix ! com
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Hi everyone,
 
To gain more RAM on our coldfire 5208 platform, I am trying to run Linux
from flash directly. 
The problem I am facing right now is that 
 
m68k-uclinux-objcopy -O binary linux-2.6.x/linux  /tmp/linux.bin.my

creates a huge image file:
 
lars@larsubu:/tmp/a3$ ls -l /tmp/linux.bin.my -rwxr-xr-x 1 lars lars
1073613792 2009-04-08 09:56 /tmp/linux.bin.my lars@larsubu:/tmp/a3$ ls
-l linux-2.6.x/linux -rwxr-xr-x 2 lars lars 2209589 2009-04-08 09:29
linux-2.6.x/linux

These are my configuration values I used for the kernel

lars@larsubu:/tmp/a3/linux-2.6.x$ grep 'CONFIG_R[O|A]M' .config

CONFIG_RAMBASE=0x40000000
CONFIG_RAMSIZE=0x00800000
CONFIG_ROM=y
CONFIG_ROMBASE=0
CONFIG_ROMVEC=0x40020
CONFIG_ROMVECSIZE=0x100
CONFIG_ROMSTART=0x40420
CONFIG_ROMSIZE=0x400000
# CONFIG_RAMKERNEL is not set
CONFIG_ROMKERNEL=y

Obviously m68k-uclinux-objcopy dumps the whole address range between the
first symbol in System.map and the last one.
So I have to extract the segments individually and let the bootloader
copy the data segment to RAM before it jumps into Linux?

lars@larsubu:/tmp/a3$ m68k-uclinux-objdump -h /tmp/a3/linux-2.6.x/linux

/tmp/a3/linux-2.6.x/linux:     file format elf32-m68k

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .romvec       000000fc  00040020  00040020  001c1000  2**0
                  CONTENTS, READONLY
  1 .text         0019f1c8  00040420  00040420  00000420  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  2 .data         00012000  40000000  40000000  001a0000  2**2
                  CONTENTS, ALLOC, LOAD, DATA
  3 .init         0000f000  40012000  40012000  001b2000  2**2
                  CONTENTS, ALLOC, LOAD, CODE
  4 .bss          0001002c  40021000  40021000  001c1000  2**4
                  ALLOC
  5 .comment      0000474c  00000000  00000000  001c10fc  2**0
                  CONTENTS, READONLY

And what about the .init segment? Looks like it has to go into RAM too.
Does it use self-modifying code?
Isn't there an easier way? It doesn't make things like firmware
upogrades easier if I have to split the kernel into 3 pieces.


If I should get beyond this hurdle, will I have do anything else then
adding the following code to
linux-2.6.x/arch/m68knommu/platform/coldfire/vectors.c to initialize the
romvec table?
 
 
#if defined(CONFIG_ROMKERNEL)
asm (
        "\t.global _start, __ramend\n\t"
        ".section .romvec\n"
"e_vectors:\n\t"
        ".long _ramend-4, _start, buserr, trap, trap, trap, trap,
trap\n\t"
        ".long trap, trap, trap, trap, trap, trap, trap, trap\n\t"
        ".long trap, trap, trap, trap, trap, trap, trap, trap\n\t"
        ".long inthandler, inthandler, inthandler, inthandler\n\t"
        ".long inthandler, inthandler, inthandler, inthandler\n\t"
        /* TRAP #0-15  33-48*/
        ".long system_call, trap, trap, trap, trap, trap, trap,
trap\n\t"
        ".long trap, trap, trap, trap, trap, trap, trap, trap\n\t"
        /* illegal traps 49-63*/
        ".long trap, trap, trap, trap, trap, trap, trap, trap\n\t"
        ".long trap, trap, trap, trap, trap, trap, trap\n\t"
        ".text\n"
"ignore: rte\n"
);
#endif

Any hint would be highly appreciated. Has someone done it successfully
on a coldfire platform?


Lars
 
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