Linux開機流程 - 從CONFIG_DEBUG_LL開始談起

利用CONFIG_DEBUG_LL除錯

在網路上查詢CONFIG_DEBUG_LL的結果
http://cateee.net/lkddb/web-lkddb/DEBUG_LL.html

arch/arm/Kconfig

The configuration item CONFIG_DEBUG_LL:

prompt: Kernel low-level debugging functions

type: tristate(三種選擇:yes/no/module)
depends on: CONFIG_DEBUG_KERNEL
(要先選擇此depend後才能有CONFIG_DEBUG_LL選項)


defined in arch/arm/Kconfig
found in Linux Kernels: before 2.6.0 version still available on 2.6.31 release
Help text

Say Y here to include definitions of printascii, printchar, printhex in the kernel. This is helpful if you are debugging code that executes before the console is initialized.

研讀Android 2.6.25原始碼後，亦有DEBUG_LL，存在於Kconfig.debug中
(但是在學長的creator_android_pxa270_defconfig裡面並沒有把此項選擇yes)

release-sourceforge\android-pxa270\kernel\linux-2.6.25-android-1.0_r1\arch\arm\Kconfig.debug

# These options are only for real kernel hackers who want to get their hands dirty.
config DEBUG_LL
 bool "Kernel low-level debugging functions"
 depends on DEBUG_KERNEL

不過在pxa300中的config檔案中就有出現了

所以要解決的事情是:
使pxa300開機時，bootloader和kernel中的machine type號碼要一致

1.到\300\src\preview-kit\linux\arch\arm\tools\mach-types

查看littleton的號碼為:1388，用小算盤換成16進制，0x56C

2.修改\300\src\preview-kit\linux\arch\arm\kernel\head.S中，ENTRY(stext)底下新增一行

LDR     r1,=0x56C

(應該可以吧...還沒測試)