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Daniel Schwierzeck6a11cf42011-07-18 07:48:07 +00001Generic SPL framework
2=====================
3
4Overview
5--------
6
7To unify all existing implementations for a secondary program loader (SPL)
8and to allow simply adding of new implementations this generic SPL framework
9has been created. With this framework almost all source files for a board
10can be reused. No code duplication or symlinking is necessary anymore.
11
12
13How it works
14------------
15
16There is a new directory TOPDIR/spl which contains only a Makefile.
17The object files are built separately for SPL and placed in this directory.
18The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
19u-boot-spl.map.
20
21During the SPL build a variable named CONFIG_SPL_BUILD is exported
22in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD.
23Source files can therefore be compiled for SPL with different settings.
24ARM-based boards have previously used the option CONFIG_PRELOADER for it.
25
26For example:
27
28ifeq ($(CONFIG_SPL_BUILD),y)
29COBJS-y += board_spl.o
30else
31COBJS-y += board.o
32endif
33
34COBJS-$(CONFIG_SPL_BUILD) += foo.o
35
36#ifdef CONFIG_SPL_BUILD
Wolfgang Denk04e5ae72011-09-11 21:24:09 +020037 foo();
Daniel Schwierzeck6a11cf42011-07-18 07:48:07 +000038#endif
39
40
41The building of SPL images can be with:
42
43#define CONFIG_SPL
44
Peter Meerwaldfd3d28e2012-02-02 12:51:03 +000045Because SPL images normally have a different text base, one has to be
46configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
Daniel Schwierzeck6a11cf42011-07-18 07:48:07 +000047defined with CONFIG_SPL_LDSCRIPT.
48
49To support generic U-Boot libraries and drivers in the SPL binary one can
50optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
51are supported:
52
53CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
54CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
55CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
56CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
57CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
58CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
59CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
60CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
61CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)
62CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
Simon Schwarz682b3a82011-09-14 15:30:54 -040063CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
Simon Schwarz12c2f1e2011-09-14 15:30:16 -040064CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o)
Simon Schwarz3a0d60c2011-09-28 05:00:27 +000065CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)
Heiko Schocher18e8ff12011-11-01 20:00:28 +000066CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)
Heiko Schocher435199f2011-11-01 20:00:29 +000067CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o)
Christian Riesch32b11272011-12-09 09:47:35 +000068CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
Pavel Machekc57b9532012-08-30 22:42:11 +020069CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)
Allen Martind22650a2012-04-19 07:58:57 +000070
71
72Normally CPU is assumed to be the same between the SPL and normal
73u-boot build. However it is possible to specify a different CPU for
74the SPL build for cases where the SPL is expected to run on a
75different CPU model from the main u-boot. This is done by specifying
76an SPL CPU in boards.cfg as follows:
77
78 normal_cpu:spl_cpu
79
Masahiro Yamadaa544ead2013-07-02 15:42:47 +090080This case CPU will be set to "normal_cpu" during the main u-boot
Allen Martind22650a2012-04-19 07:58:57 +000081build and "spl_cpu" during the SPL build.
Tom Rinif8e754d2012-08-15 07:23:20 +000082
83
84Debugging
85---------
86
87When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG
88as in most cases do_reset is not defined within SPL.
Tom Rinic3567d82012-08-15 07:23:21 +000089
90
91Estimating stack usage
92----------------------
93
94With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate
95stack usage at various points in run sequence of SPL. The -fstack-usage option
96to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that
97will give stack usage information and cflow can construct program flow.
98
99Must have gcc 4.6 or later, which supports -fstack-usage
100
1011) Build normally
1022) Perform the following shell command to generate a list of C files used in
103SPL:
104$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list
1053) Execute cflow:
106$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER
107
108cflow will spit out a number of warnings as it does not parse
109the config files and picks functions based on #ifdef. Parsing the '.i'
110files instead introduces another set of headaches. These warnings are
111not usually important to understanding the flow, however.