xref: /openbmc/u-boot/tools/env/README (revision 8946034a)
1
2This is a demo implementation of a Linux command line tool to access
3the U-Boot's environment variables.
4
5In order to cross-compile fw_printenv, run
6    make CROSS_COMPILE=<your cross-compiler prefix> env
7in the root directory of the U-Boot distribution. For example,
8    make CROSS_COMPILE=arm-linux- env
9
10For the run-time utility configuration uncomment the line
11#define CONFIG_FILE  "/etc/fw_env.config"
12in fw_env.h.
13
14For building against older versions of the MTD headers (meaning before
15v2.6.8-rc1) it is required to pass the argument "MTD_VERSION=old" to
16make.
17
18See comments in the fw_env.config file for definitions for the
19particular board.
20
21Configuration can also be done via #defines in the fw_env.h file. The
22following lines are relevant:
23
24#define HAVE_REDUND	/* For systems with 2 env sectors */
25#define DEVICE1_NAME	"/dev/mtd1"
26#define DEVICE2_NAME	"/dev/mtd2"
27#define DEVICE1_OFFSET    0x0000
28#define ENV1_SIZE         0x4000
29#define DEVICE1_ESIZE     0x4000
30#define DEVICE1_ENVSECTORS     2
31#define DEVICE2_OFFSET    0x0000
32#define ENV2_SIZE         0x4000
33#define DEVICE2_ESIZE     0x4000
34#define DEVICE2_ENVSECTORS     2
35
36Un-define HAVE_REDUND, if you want to use the utilities on a system
37that does not have support for redundant environment enabled.
38If HAVE_REDUND is undefined, DEVICE2_NAME is ignored,
39as is ENV2_SIZE and DEVICE2_ESIZE.
40
41The DEVICEx_NAME constants define which MTD character devices are to
42be used to access the environment.
43
44The DEVICEx_OFFSET constants define the environment offset within the
45MTD character device.
46
47ENVx_SIZE defines the size in bytes taken by the environment, which
48may be less then flash sector size, if the environment takes less
49then 1 sector.
50
51DEVICEx_ESIZE defines the size of the first sector in the flash
52partition where the environment resides.
53
54DEVICEx_ENVSECTORS defines the number of sectors that may be used for
55this environment instance. On NAND this is used to limit the range
56within which bad blocks are skipped, on NOR it is not used.
57
58To prevent losing changes to the environment and to prevent confusing the MTD
59drivers, a lock file at /var/lock/fw_printenv.lock is used to serialize access
60to the environment.
61