README.SPL 1.9 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 have to be
  32. configured by defining CONFIG_SPL_TEXT_BASE. The linker script have 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)