Signed-off-by: Jason Hobbs jason.hobbs@calxeda.com --- new in v4
doc/README.standard-env | 92 +++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 92 insertions(+), 0 deletions(-) create mode 100644 doc/README.standard-env
diff --git a/doc/README.standard-env b/doc/README.standard-env new file mode 100644 index 0000000..cd6c545 --- /dev/null +++ b/doc/README.standard-env @@ -0,0 +1,92 @@ +/* + * Copyright 2011, Calxeda Inc. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of + * the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, + * MA 02111-1307 USA + */ + +********************************** +* Standard Environment Variables * +********************************** + +The use of environment variables to hold addresses, file names, and +other values used during booting is a common practice across U-boot +platforms. Many platforms have variables that are used for the same +common tasks, such as pointing to a kernel in memory, or naming a +ramdisk file. Since these environment variables typically originate in +board config files rather than common code, it's easy (and has been +common) for different boards to use different environment variable +names for the exact same purpose. + +Here, we provide a of standard environment variable names that should be +used for any board that uses an environment variable that provides one +of the values listed here. That doesn't mean each board must provide all +of these variables - only that if it needs to describe one of the items +listed here, it should use the standard variable for that. Failure to +use the standard variable can result in loss of functionality when common +code is used that expects variable names to follow the standard. + +WARNING: Unfortunately, it's not yet safe to assume that a variable with +a name matching one of those below is used for the purpose listed in +this README. There are currently board configs with variable names +matching those listed below in name, but not purpose. + +TFTP Filenames +============== +Each of these variables contains the name of a file on a TFTP server. + +Variable Contains +-------- -------- +u-boot U-boot binary image +bootfile Linux kernel image +fdtfile device tree blob +ramdiskfile ramdisk image + +Load Addresses +============== +Each of these variables contains an address in RAM at which the object +is (or can be) loaded. + +Variable Contains +-------- -------- +u-boot_addr_r U-boot binary image +kernel_addr_r Linux kernel image +fdt_addr_r device tree blob +ramdisk_addr_r ramdisk image + +Flash locations +=============== +Each of these variables contains an address in NOR flash, or an offset in +NAND flash, at which the object is stored. + +Variable Contains +-------- -------- +u-boot_addr U-boot binary image +kernel_addr Linux kernel image +fdt_addr device tree blob +ramdisk_addr ramdisk image + +Other +===== +Miscellaneous + +Variable Contains +-------- -------- +bootargs Command line arguments for the kernel +loadaddr Address in RAM to load a file to, from various + sources. +serverip The IP address of the TFTP server to use when + retrieving files. +