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+/*
+ * Copyright (c) 2014 The Chromium OS Authors.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+Native Execution of U-Boot
+==========================
+
+The 'sandbox' architecture is designed to allow U-Boot to run under Linux on
+almost any hardware. To achieve this it builds U-Boot (so far as possible)
+as a normal C application with a main() and normal C libraries.
+
+All of U-Boot's architecture-specific code therefore cannot be built as part
+of the sandbox U-Boot. The purpose of running U-Boot under Linux is to test
+all the generic code, not specific to any one architecture. The idea is to
+create unit tests which we can run to test this upper level code.
+
+CONFIG_SANDBOX is defined when building a native board.
+
+The chosen vendor and board names are also 'sandbox', so there is a single
+board in board/sandbox/sandbox.
+
+CONFIG_SANDBOX_BIG_ENDIAN should be defined when running on big-endian
+machines.
+
+Note that standalone/API support is not available at present.
+
+
+Basic Operation
+---------------
+
+To run sandbox U-Boot use something like:
+
+   make sandbox_config all
+   ./u-boot
+
+Note:
+   If you get errors about 'sdl-config: Command not found' you may need to
+   install libsdl1.2-dev or similar to get SDL support. Alternatively you can
+   build sandbox without SDL (i.e. no display/keyboard support) by removing
+   the CONFIG_SANDBOX_SDL line in include/configs/sandbox.h or using:
+
+      make sandbox_config all NO_SDL=1
+      ./u-boot
+
+
+U-Boot will start on your computer, showing a sandbox emulation of the serial
+console:
+
+
+U-Boot 2014.04 (Mar 20 2014 - 19:06:00)
+
+DRAM:  128 MiB
+Using default environment
+
+In:    serial
+Out:   lcd
+Err:   lcd
+=>
+
+You can issue commands as your would normally. If the command you want is
+not supported you can add it to include/configs/sandbox.h.
+
+To exit, type 'reset' or press Ctrl-C.
+
+
+Console / LCD support
+---------------------
+
+Assuming that CONFIG_SANDBOX_SDL is defined when building, you can run the
+sandbox with LCD and keyboard emulation, using something like:
+
+   ./u-boot -d u-boot.dtb -l
+
+This will start U-Boot with a window showing the contents of the LCD. If
+that window has the focus then you will be able to type commands as you
+would on the console. You can adjust the display settings in the device
+tree file - see arch/sandbox/dts/sandbox.dts.
+
+
+Command-line Options
+--------------------
+
+Various options are available, mostly for test purposes. Use -h to see
+available options. Some of these are described below.
+
+The terminal is normally in what is called 'raw-with-sigs' mode. This means
+that you can use arrow keys for command editing and history, but if you
+press Ctrl-C, U-Boot will exit instead of handling this as a keypress.
+
+Other options are 'raw' (so Ctrl-C is handled within U-Boot) and 'cooked'
+(where the terminal is in cooked mode and cursor keys will not work, Ctrl-C
+will exit).
+
+As mentioned above, -l causes the LCD emulation window to be shown.
+
+A device tree binary file can be provided with -d. If you edit the source
+(it is stored at arch/sandbox/dts/sandbox.dts) you must rebuild U-Boot to
+recreate the binary file.
+
+To execute commands directly, use the -c option. You can specify a single
+command, or multiple commands separated by a semicolon, as is normal in
+U-Boot. Be careful with quoting as the shall will normally process and
+swallow quotes. When -c is used, U-Boot exists after the command is complete,
+but you can force it to go to interactive mode instead with -i.
+
+
+Memory Emulation
+----------------
+
+Memory emulation is supported, with the size set by CONFIG_SYS_SDRAM_SIZE.
+The -m option can be used to read memory from a file on start-up and write
+it when shutting down. This allows preserving of memory contents across
+test runs. You can tell U-Boot to remove the memory file after it is read
+(on start-up) with the --rm_memory option.
+
+To access U-Boot's emulated memory within the code, use map_sysmem(). This
+function is used throughout U-Boot to ensure that emulated memory is used
+rather than the U-Boot application memory. This provides memory starting
+at 0 and extending to the size of the emulation.
+
+
+Storing State
+-------------
+
+With sandbox you can write drivers which emulate the operation of drivers on
+real devices. Some of these drivers may want to record state which is
+preserved across U-Boot runs. This is particularly useful for testing. For
+example, the contents of a SPI flash chip should not disappear just because
+U-Boot exits.
+
+State is stored in a device tree file in a simple format which is driver-
+specific. You then use the -s option to specify the state file. Use -r to
+make U-Boot read the state on start-up (otherwise it starts empty) and -w
+to write it on exit (otherwise the stored state is left unchanged and any
+changes U-Boot made will be lost). You can also use -n to tell U-Boot to
+ignore any problems with missing state. This is useful when first running
+since the state file will be empty.
+
+The device tree file has one node for each driver - the driver can store
+whatever properties it likes in there. See 'Writing Sandbox Drivers' below
+for more details on how to get drivers to read and write their state.
+
+
+Running and Booting
+-------------------
+
+Since there is no machine architecture, sandbox U-Boot cannot actually boot
+a kernel, but it does support the bootm command. Filesystems, memory
+commands, hashing, FIT images, verified boot and many other features are
+supported.
+
+When 'bootm' runs a kernel, sandbox will exit, as U-Boot does on a real
+machine. Of course in this case, no kernel is run.
+
+It is also possible to tell U-Boot that it has jumped from a temporary
+previous U-Boot binary, with the -j option. That binary is automatically
+removed by the U-Boot that gets the -j option. This allows you to write
+tests which emulate the action of chain-loading U-Boot, typically used in
+a situation where a second 'updatable' U-Boot is stored on your board. It
+is very risky to overwrite or upgrade the only U-Boot on a board, since a
+power or other failure will brick the board and require return to the
+manufacturer in the case of a consumer device.
+
+
+Supported Drivers
+-----------------
+
+U-Boot sandbox supports these emulations:
+
+- Block devices
+- Chrome OS EC
+- GPIO
+- Host filesystem (access files on the host from within U-Boot)
+- Keyboard (Chrome OS)
+- LCD
+- Serial (for console only)
+- Sound (incomplete - see sandbox_sdl_sound_init() for details)
+- SPI
+- SPI flash
+- TPM (Trusted Platform Module)
+
+Notable omissions are networking and I2C.
+
+A wide range of commands is implemented. Filesystems which use a block
+device are supported.
+
+Also sandbox uses generic board (CONFIG_SYS_GENERIC_BOARD) and supports
+driver model (CONFIG_DM) and associated commands.
+
+
+SPI Emulation
+-------------
+
+Sandbox supports SPI and SPI flash emulation.
+
+This is controlled by the spi_sf argument, the format of which is:
+
+   bus:cs:device:file
+
+   bus    - SPI bus number
+   cs     - SPI chip select number
+   device - SPI device emulation name
+   file   - File on disk containing the data
+
+For example:
+
+ dd if=/dev/zero of=spi.bin bs=1M count=4
+ ./u-boot --spi_sf 0:0:M25P16:spi.bin
+
+With this setup you can issue SPI flash commands as normal:
+
+=>sf probe
+SF: Detected M25P16 with page size 64 KiB, total 2 MiB
+=>sf read 0 0 10000
+SF: 65536 bytes @ 0x0 Read: OK
+=>
+
+Since this is a full SPI emulation (rather than just flash), you can
+also use low-level SPI commands:
+
+=>sspi 0:0 32 9f
+FF202015
+
+This is issuing a READ_ID command and getting back 20 (ST Micro) part
+0x2015 (the M25P16).
+
+Drivers are connected to a particular bus/cs using sandbox's state
+structure (see the 'spi' member). A set of operations must be provided
+for each driver.
+
+
+Configuration settings for the curious are:
+
+CONFIG_SANDBOX_SPI_MAX_BUS
+	The maximum number of SPI buses supported by the driver (default 1).
+
+CONFIG_SANDBOX_SPI_MAX_CS
+	The maximum number of chip selects supported by the driver
+	(default 10).
+
+CONFIG_SPI_IDLE_VAL
+	The idle value on the SPI bus
+
+
+Writing Sandbox Drivers
+-----------------------
+
+Generally you should put your driver in a file containing the word 'sandbox'
+and put it in the same directory as other drivers of its type. You can then
+implement the same hooks as the other drivers.
+
+To access U-Boot's emulated memory, use map_sysmem() as mentioned above.
+
+If your driver needs to store configuration or state (such as SPI flash
+contents or emulated chip registers), you can use the device tree as
+described above. Define handlers for this with the SANDBOX_STATE_IO macro.
+See arch/sandbox/include/asm/state.h for documentation. In short you provide
+a node name, compatible string and functions to read and write the state.
+Since writing the state can expand the device tree, you may need to use
+state_setprop() which does this automatically and avoids running out of
+space. See existing code for examples.
+
+
+Testing
+-------
+
+U-Boot sandbox can be used to run various tests, mostly in the test/
+directory. These include:
+
+  command_ut
+     - Unit tests for command parsing and handling
+  compression
+     - Unit tests for U-Boot's compression algorithms, useful for
+       security checking. It supports gzip, bzip2, lzma and lzo.
+  driver model
+     - test/dm/test-dm.sh to run these.
+  image
+     - Unit tests for images:
+          test/image/test-imagetools.sh - multi-file images
+          test/image/test-fit.py        - FIT images
+  tracing
+     - test/trace/test-trace.sh tests the tracing system (see README.trace)
+  verified boot
+      - See test/vboot/vboot_test.sh for this
+
+If you change or enhance any of the above subsystems, you shold write or
+expand a test and include it with your patch series submission. Test
+coverage in U-Boot is limited, as we need to work to improve it.
+
+Note that many of these tests are implemented as commands which you can
+run natively on your board if desired (and enabled).
+
+It would be useful to have a central script to run all of these.
+
+--
+Simon Glass <sjg@chromium.org>
+Updated 22-Mar-14