Re: small custom bootloader to start an app stored in flash

[Edgar Grimberg <edgar dot grimberg at gmail dot com>]

>
> May be I am missing something in the understanding of the principles.
>

I don't see anything obviously broken (I guess you would have spotted it).

If you have a JTAG debugger, now it's a good time to make use of it:
1. Check that you don't reach the infinite loop in your bootloader application.
2. Insert a hardware breakpoint at address 0x08020000, to see if you
call the correct address from the bootloader.
3. Try single stepping when you get to 0x08020000, see if the code makes sense.
4. Try starting your application (0x08020000) from the debugger
directly, see if you get the printf.


> ROM startup build copies .data and .bss sections into ram, probably these
> sections data gets overwritten.

They should get overwritten by the app startup sequence. This is OK.

> Do I need to shift addresses of SECTION_sram, SECTION_data, SECTION_bss  in
> app's memory layout?

No, you won't need anything from the bootloader, you'll never return
execution to the bootloader (unless you reset the board).

> $ arm-none-eabi-readelf -h app.elf
> ELF Header:
>   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
>   Class:                             ELF32
>   Data:                              2's complement, little endian
>   Version:                           1 (current)
>   OS/ABI:                            UNIX - System V
>   ABI Version:                       0
>   Type:                              EXEC (Executable file)
>   Machine:                           ARM
>   Version:                           0x1
>   Entry point address:               0x8020111

As pointed previously, there is something strange with this address.
Can you try jumping to it from the bootloader?

Edgar


>   Start of program headers:          52 (bytes into file)
>   Start of section headers:          24148 (bytes into file)
>   Flags:                             0x5000002, has entry point, Version5
> EABI
>   Size of this header:               52 (bytes)
>   Size of program headers:           32 (bytes)
>   Number of program headers:         3
>   Size of section headers:           40 (bytes)
>   Number of section headers:         12
>   Section header string table index: 11
>
> $ arm-none-eabi-objdump -h app.elf
>
> app.elf:     file format elf32-littlearm
>
> Sections:
> Idx Name          Size      VMA       LMA       File off  Algn
>   0 .rom_vectors  00000008  08020000  08020000  00000098  2**0
>                   CONTENTS, ALLOC, LOAD, READONLY, CODE
>   1 .ARM.extab    0000003c  08020008  08020008  000000a0  2**2
>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
>   2 .ARM.exidx    000000c8  08020048  08020048  000000e0  2**2
>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
>   3 .text         0000586c  08020110  08020110  000001a8  2**3
>                   CONTENTS, ALLOC, LOAD, READONLY, CODE
>   4 .rodata       0000010d  08025980  08025980  00005a18  2**2
>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
>   5 .eh_frame     00000008  08025a90  08025a90  00005b25  2**0
>                   ALLOC
>   6 .data         00000268  20000288  08025a98  00005b28  2**3
>                   CONTENTS, ALLOC, LOAD, DATA
>   7 .bss          000034e8  200004f0  08025d00  00005d90  2**3
>                   ALLOC
>   8 .ARM.attributes 0000002d  00000000  00000000  00005d90  2**0
>                   CONTENTS, READONLY
>   9 .comment      0000002a  00000000  00000000  00005dbd  2**0
>                   CONTENTS, READONLY
>
>
>
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>

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