u-boot/doc/README.falcon

1 U-Boot Falcon Mode
5 ------------
11 to boot a Linux kernel (or whatever image) without a full blown U-Boot.
13 Falcon Mode relies on the SPL framework. In fact, to make booting faster,
14 U-Boot is split into two parts: the SPL (Secondary Program Loader) and U-Boot
15 image. In most implementations, SPL is used to start U-Boot when booting from
16 a mass storage, such as NAND or SD-Card. SPL has now support for other media,
18 required initialization. SPL mainly initializes the RAM controller, and then
19 copies U-Boot image into the memory.
22 from SPL. A new command is added to U-Boot to prepare the parameters that SPL
28 With Falcon Mode, this snapshot can be saved into persistent storage and SPL is
31 To boot the kernel, these steps under a Falcon-aware U-Boot are required:
33 1. Boot the board into U-Boot.
34 After loading the desired legacy-format kernel image into memory (and DT as
35 well, if used), use the "spl export" command to generate the kernel parameters
36 area or the DT.  U-Boot runs as when it boots the kernel, but stops before
43 3. Boot the board into Falcon Mode. SPL will load the kernel and copy
45 If a valid uImage is not found at the defined location, U-Boot will be
48 It is required to implement a custom mechanism to select if SPL loads U-Boot
52 reading a character from the SPL console if CONFIG_SPL_CONSOLE is set.
55 SPL that U-Boot is not the only available image that SPL is able to start.
58 ----------------------------
59 CONFIG_CMD_SPL		Enable the "spl export" command.
60 			The command "spl export" is then available in U-Boot
63 				copied by SPL.
75 ------------------------------------
78 	Called from SPL before starting the kernel
81 		Returns "0" if SPL should start the kernel, "1" if U-Boot
85 ---------------------
91 			any other value to fall back to U-Boot (including
94 			rather than the hard-coded value.
96 			mode rather than the hard-coded value.
98 Using spl command
99 -----------------
101 spl - SPL configuration
105 spl export <img=atags|fdt> [kernel_addr] [initrd_addr] [fdt_addr ]
108 kernel_addr	: kernel is loaded as part of the boot process, but it is not started.
111 		  can be set to "-" if fdt_addr without initrd_addr is used
114 The spl export command does not write to a storage media. The user is
117 after each run of 'spl export'. Unfortunately the position of temporary
120 However at the end of an succesful 'spl export' run it will print the
128 to the pre-defined address in persistent storage
133 The "spl export" command is prepared to work with ATAGS and FDT. However,
139 --------------------------------
144 device nand0 <omap2-nand.0>, # parts = 9
147  1: u-boot              0x00100000      0x00080000      0
164 twister => spl export atags 0x82000000
166    Image Name:   Linux-3.5.0-rc4-14089-gda0b7f4
197 The kernel is loaded directly by the SPL without passing through U-Boot.
200 -------------------------------
202 To boot the Linux kernel from the SPL, the DT blob (fdt) needs to get
203 prepard/patched first. U-Boot usually inserts some dynamic values into