summaryrefslogtreecommitdiffstats
path: root/Documentation/arm/Booting
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/arm/Booting')
-rw-r--r--Documentation/arm/Booting171
1 files changed, 0 insertions, 171 deletions
diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting
deleted file mode 100644
index a341d87..0000000
--- a/Documentation/arm/Booting
+++ /dev/null
@@ -1,171 +0,0 @@
- 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 specifying the port, and
-serial format options as described in
-
- 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 boot data
-------------------
-
-Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED
-New boot loaders: MANDATORY
-
-The boot loader must provide either a tagged list or a dtb image for
-passing configuration data to the kernel. The physical address of the
-boot data is passed to the kernel in register r2.
-
-4a. Setup the kernel tagged list
---------------------------------
-
-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.
-
-4b. Setup the device tree
--------------------------
-
-The boot loader must load a device tree image (dtb) into system ram
-at a 64bit aligned address and initialize it with the boot data. The
-dtb format is documented in Documentation/devicetree/booting-without-of.txt.
-The kernel will look for the dtb magic value of 0xd00dfeed at the dtb
-physical address to determine if a dtb has been passed instead of a
-tagged list.
-
-The boot loader must pass at a minimum the size and location of the
-system memory, and the root filesystem location. The dtb must be
-placed in a region of memory where the kernel decompressor will not
-overwrite it. The recommended placement is in the first 16KiB of RAM
-with the caveat that it may not be located at physical address 0 since
-the kernel interprets a value of 0 in r2 to mean neither a tagged list
-nor a dtb were passed.
-
-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:
-
-- Quiesce all DMA capable devices so that memory does not get
- corrupted by bogus network packets or disk data. This will save
- you many hours of debug.
-
-- CPU register settings
- r0 = 0,
- r1 = machine type number discovered in (3) above.
- r2 = physical address of tagged list in system RAM, or
- physical address of device tree block (dtb) 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.
-
- On CPUs supporting the ARM instruction set, the entry must be
- made in ARM state, even for a Thumb-2 kernel.
-
- On CPUs supporting only the Thumb instruction set such as
- Cortex-M class CPUs, the entry must be made in Thumb state.