patch-2.4.21 linux-2.4.21/Documentation/arm/Booting

• Lines: 138
• Date: 2003-06-13 07:51:29.000000000 -0700
• Orig file: linux-2.4.20/Documentation/arm/Booting
• Orig date: 1969-12-31 16:00:00.000000000 -0800

diff -urN linux-2.4.20/Documentation/arm/Booting linux-2.4.21/Documentation/arm/Booting
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+			Booting ARM Linux
+			=================
+
+Author:	Russell King
+Date  : 18 May 2002
+
+The following documentation is relevant to 2.4.18-rmk6 and beyond.
+
+In order to boot ARM Linux, you require a boot loader, which is a small
+program that runs before the main kernel.  The boot loader is expected
+to initialise various devices, and eventually call the Linux kernel,
+passing information to the kernel.
+
+Essentially, the boot loader should provide (as a minimum) the
+following:
+
+1. Setup and initialise the RAM.
+2. Initialise one serial port.
+3. Detect the machine type.
+4. Setup the kernel tagged list.
+5. Call the kernel image.
+
+
+1. Setup and initialise RAM
+---------------------------
+
+Existing boot loaders:		MANDATORY
+New boot loaders:		MANDATORY
+
+The boot loader is expected to find and initialise all RAM that the
+kernel will use for volatile data storage in the system.  It performs
+this in a machine dependent manner.  (It may use internal algorithms
+to automatically locate and size all RAM, or it may use knowledge of
+the RAM in the machine, or any other method the boot loader designer
+sees fit.)
+
+
+2. Initialise one serial port
+-----------------------------
+
+Existing boot loaders:		OPTIONAL, RECOMMENDED
+New boot loaders:		OPTIONAL, RECOMMENDED
+
+The boot loader should initialise and enable one serial port on the
+target.  This allows the kernel serial driver to automatically detect
+which serial port it should use for the kernel console (generally
+used for debugging purposes, or communication with the target.)
+
+As an alternative, the boot loader can pass the relevant 'console='
+option to the kernel via the tagged lists specifing the port, and
+serial format options as described in
+
+       linux/Documentation/kernel-parameters.txt.
+
+
+3. Detect the machine type
+--------------------------
+
+Existing boot loaders:		OPTIONAL
+New boot loaders:		MANDATORY
+
+The boot loader should detect the machine type its running on by some
+method.  Whether this is a hard coded value or some algorithm that
+looks at the connected hardware is beyond the scope of this document.
+The boot loader must ultimately be able to provide a MACH_TYPE_xxx
+value to the kernel. (see linux/arch/arm/tools/mach-types).
+
+
+4. Setup the kernel tagged list
+-------------------------------
+
+Existing boot loaders:		OPTIONAL, HIGHLY RECOMMENDED
+New boot loaders:		MANDATORY
+
+The boot loader must create and initialise the kernel tagged list.
+A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE.
+The ATAG_CORE tag may or may not be empty.  An empty ATAG_CORE tag
+has the size field set to '2' (0x00000002).  The ATAG_NONE must set
+the size field to zero.
+
+Any number of tags can be placed in the list.  It is undefined
+whether a repeated tag appends to the information carried by the
+previous tag, or whether it replaces the information in its
+entirety; some tags behave as the former, others the latter.
+
+The boot loader must pass at a minimum the size and location of
+the system memory, and root filesystem location.  Therefore, the
+minimum tagged list should look:
+
+	+-----------+
+base ->	| ATAG_CORE |  |
+	+-----------+  |
+	| ATAG_MEM  |  | increasing address
+	+-----------+  |
+	| ATAG_NONE |  |
+	+-----------+  v
+
+The tagged list should be stored in system RAM.
+
+The tagged list must be placed in a region of memory where neither
+the kernel decompressor nor initrd 'bootp' program will overwrite
+it.  The recommended placement is in the first 16KiB of RAM.
+
+5. Calling the kernel image
+---------------------------
+
+Existing boot loaders:		MANDATORY
+New boot loaders:		MANDATORY
+
+There are two options for calling the kernel zImage.  If the zImage
+is stored in flash, and is linked correctly to be run from flash,
+then it is legal for the boot loader to call the zImage in flash
+directly.
+
+The zImage may also be placed in system RAM (at any location) and
+called there.  Note that the kernel uses 16K of RAM below the image
+to store page tables.  The recommended placement is 32KiB into RAM.
+
+In either case, the following conditions must be met:
+
+- CPU register settings
+  r0 = 0,
+  r1 = machine type number discovered in (3) above.
+  r2 = physical address of tagged list in system RAM.
+
+- CPU mode
+  All forms of interrupts must be disabled (IRQs and FIQs)
+  The CPU must be in SVC mode.  (A special exception exists for Angel)
+
+- Caches, MMUs
+  The MMU must be off.
+  Instruction cache may be on or off.
+  Data cache must be off.
+
+- The boot loader is expected to call the kernel image by jumping
+  directly to the first instruction of the kernel image.
+