X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=README;h=57426e55eae5ae16c0581f0ba923cafaa7ad50f7;hb=e736570cc38cbdef2d0f8f9f4862ca17795ba6d0;hp=febefb50c24a9bc4efacb6d4224ef17b4b244763;hpb=1606b34aa50804227806971dbb6b82ea0bf81f55;p=oweals%2Fu-boot.git

diff --git a/README b/README
index febefb50c2..57426e55ea 100644
--- a/README
+++ b/README
@@ -273,6 +273,75 @@ run some of U-Boot's tests.
 See board/sandbox/README.sandbox for more details.
 
 
+Board Initialisation Flow:
+--------------------------
+
+This is the intended start-up flow for boards. This should apply for both
+SPL and U-Boot proper (i.e. they both follow the same rules). At present SPL
+mostly uses a separate code path, but the funtion names and roles of each
+function are the same. Some boards or architectures may not conform to this.
+At least most ARM boards which use CONFIG_SPL_FRAMEWORK conform to this.
+
+Execution starts with start.S with three functions called during init after
+that. The purpose and limitations of each is described below.
+
+lowlevel_init():
+	- purpose: essential init to permit execution to reach board_init_f()
+	- no global_data or BSS
+	- there is no stack (ARMv7 may have one but it will soon be removed)
+	- must not set up SDRAM or use console
+	- must only do the bare minimum to allow execution to continue to
+		board_init_f()
+	- this is almost never needed
+	- return normally from this function
+
+board_init_f():
+	- purpose: set up the machine ready for running board_init_r():
+		i.e. SDRAM and serial UART
+	- global_data is available
+	- stack is in SRAM
+	- BSS is not available, so you cannot use global/static variables,
+		only stack variables and global_data
+
+	Non-SPL-specific notes:
+	- dram_init() is called to set up DRAM. If already done in SPL this
+		can do nothing
+
+	SPL-specific notes:
+	- you can override the entire board_init_f() function with your own
+		version as needed.
+	- preloader_console_init() can be called here in extremis
+	- should set up SDRAM, and anything needed to make the UART work
+	- these is no need to clear BSS, it will be done by crt0.S
+	- must return normally from this function (don't call board_init_r()
+		directly)
+
+Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
+this point the stack and global_data are relocated to below
+CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
+memory.
+
+board_init_r():
+	- purpose: main execution, common code
+	- global_data is available
+	- SDRAM is available
+	- BSS is available, all static/global variables can be used
+	- execution eventually continues to main_loop()
+
+	Non-SPL-specific notes:
+	- U-Boot is relocated to the top of memory and is now running from
+		there.
+
+	SPL-specific notes:
+	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
+		CONFIG_SPL_STACK_R_ADDR points into SDRAM
+	- preloader_console_init() can be called here - typically this is
+		done by defining CONFIG_SPL_BOARD_INIT and then supplying a
+		spl_board_init() function containing this call
+	- loads U-Boot or (in falcon mode) Linux
+
+
+
 Configuration Options:
 ----------------------
 
@@ -621,6 +690,21 @@ The following options need to be configured:
 		exists, unlike the similar options in the Linux kernel. Do not
 		set these options unless they apply!
 
+		NOTE: The following can be machine specific errata. These
+		do have ability to provide rudimentary version and machine
+		specific checks, but expect no product checks.
+		CONFIG_ARM_ERRATA_430973
+		CONFIG_ARM_ERRATA_454179
+		CONFIG_ARM_ERRATA_621766
+		CONFIG_ARM_ERRATA_798870
+
+- Tegra SoC options:
+		CONFIG_TEGRA_SUPPORT_NON_SECURE
+
+		Support executing U-Boot in non-secure (NS) mode. Certain
+		impossible actions will be skipped if the CPU is in NS mode,
+		such as ARM architectural timer initialization.
+
 - Driver Model
 		Driver model is a new framework for devices in U-Boot
 		introduced in early 2014. U-Boot is being progressively
@@ -734,7 +818,6 @@ The following options need to be configured:
 
 		Enable removing of devices.
 
-
 - Linux Kernel Interface:
 		CONFIG_CLOCKS_IN_MHZ
 
@@ -4353,6 +4436,9 @@ to save the current settings.
 	  If defined, specified the chip address of the EEPROM device.
 	  The default address is zero.
 
+	- CONFIG_SYS_I2C_EEPROM_BUS:
+	  If defined, specified the i2c bus of the EEPROM device.
+
 	- CONFIG_SYS_EEPROM_PAGE_WRITE_BITS:
 	  If defined, the number of bits used to address bytes in a
 	  single page in the EEPROM device.  A 64 byte page, for example