README.SPL 3.7 KB

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  1. Generic SPL framework
  2. =====================
  3. Overview
  4. --------
  5. To unify all existing implementations for a secondary program loader (SPL)
  6. and to allow simply adding of new implementations this generic SPL framework
  7. has been created. With this framework almost all source files for a board
  8. can be reused. No code duplication or symlinking is necessary anymore.
  9. How it works
  10. ------------
  11. There is a new directory TOPDIR/spl which contains only a Makefile.
  12. The object files are built separately for SPL and placed in this directory.
  13. The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
  14. u-boot-spl.map.
  15. During the SPL build a variable named CONFIG_SPL_BUILD is exported
  16. in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD.
  17. Source files can therefore be compiled for SPL with different settings.
  18. ARM-based boards have previously used the option CONFIG_PRELOADER for it.
  19. For example:
  20. ifeq ($(CONFIG_SPL_BUILD),y)
  21. COBJS-y += board_spl.o
  22. else
  23. COBJS-y += board.o
  24. endif
  25. COBJS-$(CONFIG_SPL_BUILD) += foo.o
  26. #ifdef CONFIG_SPL_BUILD
  27. foo();
  28. #endif
  29. The building of SPL images can be with:
  30. #define CONFIG_SPL
  31. Because SPL images normally have a different text base, one has to be
  32. configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
  33. defined with CONFIG_SPL_LDSCRIPT.
  34. To support generic U-Boot libraries and drivers in the SPL binary one can
  35. optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
  36. are supported:
  37. CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
  38. CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
  39. CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
  40. CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
  41. CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
  42. CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
  43. CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
  44. CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
  45. CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)
  46. CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
  47. CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
  48. CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o)
  49. CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)
  50. CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)
  51. CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o)
  52. CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
  53. Normally CPU is assumed to be the same between the SPL and normal
  54. u-boot build. However it is possible to specify a different CPU for
  55. the SPL build for cases where the SPL is expected to run on a
  56. different CPU model from the main u-boot. This is done by specifying
  57. an SPL CPU in boards.cfg as follows:
  58. normal_cpu:spl_cpu
  59. This this case CPU will be set to "normal_cpu" during the main u-boot
  60. build and "spl_cpu" during the SPL build.
  61. Debugging
  62. ---------
  63. When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG
  64. as in most cases do_reset is not defined within SPL.
  65. Estimating stack usage
  66. ----------------------
  67. With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate
  68. stack usage at various points in run sequence of SPL. The -fstack-usage option
  69. to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that
  70. will give stack usage information and cflow can construct program flow.
  71. Must have gcc 4.6 or later, which supports -fstack-usage
  72. 1) Build normally
  73. 2) Perform the following shell command to generate a list of C files used in
  74. SPL:
  75. $ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list
  76. 3) Execute cflow:
  77. $ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER
  78. cflow will spit out a number of warnings as it does not parse
  79. the config files and picks functions based on #ifdef. Parsing the '.i'
  80. files instead introduces another set of headaches. These warnings are
  81. not usually important to understanding the flow, however.