path: root/doc
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authorKarsten Merker <>2015-03-21 14:15:38 +0100
committerTom Rini <>2015-03-28 12:07:45 -0400
commit8c2492901998a76e083ed0875372c141da084d86 (patch)
treeed77f59bc73f26d6b50df6fc6db2958aed715a3b /doc
parent1344bd7ebec4e0d2c0e2da0133b957d3cf93357b (diff)
Document config_distro_bootcmd environment variables for interactive booting.
config_distro_bootcmd.h defines a common boot environment for multiple platforms, including several environment variables that are intended for interactive use by an end-user. Document which variables are considered public interfaces that must remain compatible in future u-boot versions. Signed-off-by: Karsten Merker <> Acked-by: Stephen Warren <>
Diffstat (limited to 'doc')
1 files changed, 47 insertions, 0 deletions
diff --git a/doc/README.distro b/doc/README.distro
index dd0f1c7b6a..0308a4c73a 100644
--- a/doc/README.distro
+++ b/doc/README.distro
@@ -1,6 +1,7 @@
* (C) Copyright 2014 Red Hat Inc.
* Copyright (c) 2014-2015, NVIDIA CORPORATION. All rights reserved.
+ * Copyright (C) 2015 K. Merker <>
* SPDX-License-Identifier: GPL-2.0+
@@ -339,3 +340,49 @@ scan_dev_for_scripts:
If you want to disable boot.scr on all disks, set the value to something
innocuous, e.g. setenv scan_dev_for_scripts true.
+Interactively booting from a specific device at the u-boot prompt
+For interactively booting from a user-selected device at the u-boot command
+prompt, the environment provides predefined bootcmd_<target> variables for
+every target defined in boot_targets, which can be run be the user.
+If the target is a storage device, the format of the target is always
+<device type><device number>, e.g. mmc0. Specifying the device number is
+mandatory for storage devices, even if only support for a single instance
+of the storage device is actually implemented.
+For network targets (dhcp, pxe), only the device type gets specified;
+they do not have a device number.
+ - run bootcmd_usb0
+ boots from the first USB mass storage device
+ - run bootcmd_mmc1
+ boots from the second MMC device
+ - run bootcmd_pxe
+ boots by tftp using a pxelinux.cfg
+The list of possible targets consists of:
+- network targets
+ * dhcp
+ * pxe
+- storage targets (to which a device number must be appended)
+ * mmc
+ * sata
+ * scsi
+ * ide
+ * usb
+Other *boot* variables than the ones defined above are only for internal use
+of the boot environment and are not guaranteed to exist or work in the same
+way in future u-boot versions. In particular the <device type>_boot
+variables (e.g. mmc_boot, usb_boot) are a strictly internal implementation
+detail and must not be used as a public interface.
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