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[people/ms/u-boot.git] / doc / README.falcon

diff --git a/doc/README.falcon b/doc/README.falcon
index 93e855d20eac55a4779c583f7da68c3299c11055..9a7f0bc23515089d1a5e8e968c7db58f051cb613 100644 (file)
--- a/doc/README.falcon
+++ b/doc/README.falcon
@@ -31,9 +31,10 @@ informed to load it before running the kernel.
 To boot the kernel, these steps under a Falcon-aware U-Boot are required:
 
 1. Boot the board into U-Boot.
-Use the "spl export" command to generate the kernel parameters area or the DT.
-U-Boot runs as when it boots the kernel, but stops before passing the control
-to the kernel.
+After loading the desired legacy-format kernel image into memory (and DT as
+well, if used), use the "spl export" command to generate the kernel parameters
+area or the DT.  U-Boot runs as when it boots the kernel, but stops before
+passing the control to the kernel.
 
 2. Save the prepared snapshot into persistent media.
 The address where to save it must be configured into board configuration
@@ -41,6 +42,8 @@ file (CONFIG_CMD_SPL_NAND_OFS for NAND).
 
 3. Boot the board into Falcon Mode. SPL will load the kernel and copy
 the parameters which are saved in the persistent area to the required address.
+If a valid uImage is not found at the defined location, U-Boot will be
+booted instead.
 
 It is required to implement a custom mechanism to select if SPL loads U-Boot
 or another image.
@@ -78,6 +81,19 @@ spl_start_uboot() : required
                Returns "0" if SPL should start the kernel, "1" if U-Boot
                must be started.
 
+Environment variables
+---------------------
+
+A board may chose to look at the environment for decisions about falcon
+mode.  In this case the following variables may be supported:
+
+boot_os :              Set to yes/Yes/true/True/1 to enable booting to OS,
+                       any other value to fall back to U-Boot (including
+                       unset)
+falcon_args_file :     Filename to load as the 'args' portion of falcon mode
+                       rather than the hard-coded value.
+falcon_image_file :    Filename to load as the OS image portion of falcon
+                       mode rather than the hard-coded value.
 
 Using spl command
 -----------------
@@ -102,7 +118,12 @@ after each run of 'spl export'. Unfortunately the position of temporary
 storage can not be predicted nor provided at commandline, it depends
 highly on your system setup and your provided data (ATAGS or FDT).
 However at the end of an succesful 'spl export' run it will print the
-RAM address of temporary storage.
+RAM address of temporary storage. The RAM address of FDT will also be
+set in the environment variable 'fdtargsaddr', the new length of the
+prepared FDT will be set in the environment variable 'fdtargslen'.
+These environment variables can be used in scripts for writing updated
+FDT to persistent storage.
+
 Now the user have to save the generated BLOB from that printed address
 to the pre-defined address in persistent storage
 (CONFIG_CMD_SPL_NAND_OFS in case of NAND).