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124	decky	1	\chapter{Boot Loading Process}
		2
		3	The startup of HelenOS happens in several steps.
		4	Depending on the platform these steps can be either
		5	described as \textit{piggybacker loading}:
		6
		7	\begin{enumerate}
		8	\item Platform boot loader loads the piggybacker image
		9	and jumps to its entry point.
		10	\item The piggybacker unwraps the kernel image and
		11	the images of the initial user space tasks, creates
		12	a boot information structure and jumps to the
		13	entry point of the kernel.
		14	\item The kernel initializes and runs the initial tasks
		15	according the boot information structure from the
		16	piggybacker.
		17	\end{enumerate}
		18
		19	If the platform supports a more sophisticated native boot loader,
		20	a \textit{multiboot loading} contains following steps:
		21
		22	\begin{enumerate}
		23	\item Platform boot loader loads the kernel image and initial
		24	user space tasks, creates a boot information structure
		25	and jumps to the entry point of the kernel.
		26	\item The kernel initializes and runs the initial tasks
		27	according the boot information structure from the
		28	boot loader.
		29	\end{enumerate}
		30
		31	A third kind of boot loading occurs on platforms with no support
		32	of boot loader. It is called \textit{image loading} and is
		33	used mostly on simulated architectures.
		34
		35	\begin{enumerate}
		36	\item The kernel and initial user space images are placed
		37	on well-known physical memory locations (usually
		38	by a simulator configuration file). The execution
		39	starts directly on the kernel entry point.
		40	\item The kernel initializes and runs a previously hardwired
		41	number of initial user space tasks.
		42	\end{enumerate}
		43
		44	The following sections describe the particual features of the
149	palkovsky	45	boot loading process on the supported platforms. Sample
		46	configuration files for all simulators are in the directory
		47	{\em kernel/contrib/conf}.
124	decky	48
		49	\section{IA-32 and AMD64}
		50
		51	On both platforms HelenOS depends on a boot loader which
		52	supports the Multiboot Specification (i.e. GRUB). The kernel
		53	image (usually called \texttt{image.bin}) is loaded by the
		54	boot loader just above the 1st megabyte of the physical
149	palkovsky	55	memory (the exact location is 1081344 bytes). Modules loaded by
		56	GRUB are automatically detected by the kernel and after initialization
		57	they are started as userspace tasks. The GRUB loading is the
		58	easiest in terms of using userspace tasks.
		59
		60	An example GRUB configuration file {\em menu.lst}:
		61	\begin{verbatim}
		62	title=HelenOS
		63	root (cd)
		64	kernel /boot/kernel.bin
		65	module /boot/ns
		66	module /boot/init
		67	module /boot/pci
		68	module /boot/fb
		69	module /boot/kbd
		70	module /boot/console
		71	module /boot/tetris
		72	module /boot/ipcc
		73	module /boot/klog
		74	\end{verbatim}
		75
		76	\section{32-bit MIPS}
		77	The MIPS port is fully supported in the {\em msim} and {\em gxemul} simulators.
		78	These simulators allow specifying a memory contents of the simulated
		79	computer. Unfortunately, the autodetection of loaded modules does
		80	not work. In order to change number of loaded modules, the file
		81	kernel/arch/mips32/src/mips32.c must be modified.
		82
		83	Sample msim configuration file:
		84	\begin{verbatim}
		85	add dcpu mips1
		86
		87	add rwm mainmem 0x0 8M load "/dev/zero"
		88	add rom startmem 0x1fc00000 1024k load "image.boot"
		89	add rwm ns 0x01000000 1M load "../uspace/ns/ns"
		90	add rwm kbd 0x01100000 1M load "../uspace/fb/fb"
		91	add rwm fb 0x01200000 1M load "../uspace/kbd/kbd"
		92	add rwm console 0x01300000 1M load "../uspace/console/console"
		93	add rwm init 0x01400000 1M load "../uspace/init/init"
		94	add rwm tetris 0x01500000 1M load "../uspace/tetris/tetris"
		95	\end{verbatim}
		96
		97	Sample gxemul command line arguments
		98	\begin{verbatim}
		99	gxemul -E testmips -X 0x81800000:../uspace/ns/ns 0x81900000:../uspace/kbd/kbd 0x81a00000:../uspace/fb/fb 0x81b00000:../uspace/init/init 0x81c00000:../uspace/console/console 0x81d00000:../uspace/tetris/tetris kernel.bin
		100	\end{verbatim}
		101
		102	The kernel can boot on the SGI Indy (and probably other SGI computers
		103	with 32-bit ARC firmware). It uses ARC for output and input. When
		104	the kernel is compiled to be loaded on the SGI Indy, an ECOFF image
		105	is created which can be later loaded directly with ARC boot loader
		106	e.g. using BOOTP protocol.
		107
		108	\section{IA64}
		109	The IA64 port is supported on the ski simulator. The situation is very similar
		110	to the MIPS loader - the loaded modules must be loaded on correct addresses in
		111	the ski configuration file and specified in the file
		112	kernel/arch/ia64/src/ia64.c.
		113
		114	Sample IA64 configuration file:
		115	\begin{verbatim}
		116	load kernel.bin
		117	romload ../uspace/ns/ns 0x400000
		118	romload ../uspace/init/init 0x800000
		119	romload ../uspace/console/console 0xc00000
		120	romload ../uspace/fb/fb 0x1000000
		121	romload ../uspace/kbd/kbd 0x1400000
		122	romload ../uspace/tetris/tetris 0x1800000
		123	romload ../uspace/klog/klog 0x1c00000
		124	romload ../uspace/ipcc/ipcc 0x2000000
		125	\end{verbatim}
		126
		127	\section{Power PC}
		128	The PowerPC boot image contains complete kernel with user tasks.
		129	The loader build system automatically creates such image using information
		130	residing in boot/arch/ppc32/loader/Makefile.inc. The variable COMPONENTS
		131	specifies, which tasks will be loaded into the image.

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