BootSequence < PPCEmbedded

%SECTION0{name=BootSequence}% Boot Sequence

The Linux boot sequence is more complicated than your average
embedded operating system, and there are many more options for
configuring things. In general, the boot sequence goes like this:

   1 Processor comes out of reset and branches to the
     [[ROMMonitor][ROM startup code]].
   1 The [[ROMMonitor][ROM startup code]] initializes the CPU and memory controller, 
     performing only minimal initialization of on-chip devices, such as
     the console serial port (typically SMC1 on 8xx devices) to provide
     boot diagnostic messages. It also sets up the
     %REF{type=Section,topic=Kernel,name=MemoryMap,text="memory map"}% for the
     [[Kernel][kernel]] to use in a format that is consistent across platforms, and then jumps
     to the %REF{type=Section,topic=BootLoader,name=BootLoader,text="boot loader"}%.
   1 The [[BootLoader][boot loader]] decompresses the [[Kernel][kernel]]
     into RAM, and jumps to it.
   1 The [[Kernel][kernel]] sets up the caches, initializes each of the hardware devices
     via the init function in each driver, mounts the
     [[RootFilesystem][root file system]] and execs
     the init process, which is the ultimate parent of all user mode processes,
     typically =/sbin/initd=.
   1 Executing the first program linked against the shared C
     [[RuntimeLibrary][runtime library]] (often init) causes the shared
     runtime library to be loaded.
   1 In a typical Linux system, init reads =/etc/inittab= to execute the 
     appropriate run control script from =/etc/rc.d=, which execute the start
     scripts to initialize networking and other system services.

In minimal embedded systems,  is commonly replaced with a simple
C program or shell script to start the appropriate services and
[[Applications][application programs]], since the conventional
rc scripts are often overkill.
6. Programming the Target		1. Introduction		8. ROM Monitor
Prev		Home		Next