u-boot/board/lego/ev3

Summary
=======

LEGO MINDSTORMS EV3 is a toy robot produced by the LEGO Group. It is based
on the davinci da850 evm. The EV3 has a 16MB spi flash and a SDHC microSD card
reader.

Booting
=======

The EV3 contains a bootloader in EEPROM that loads u-boot.bin from address 0x0
of the SPI flash memory (with a size of 256KiB!). Because the EEPROM is read-
only and it takes care of low level configuration (PLL and DDR), we don't use
U-Boot to produce an SPL image.

Using the default configuration, U-Boot had a boot scrips that works as follows:

* Check to see if microSD card is present
* If it is, try to load boot.scr from the first FAT partition
* If loading boot.scr was successful, run it
* Otherwise, try loading uEnv.txt
* If loading uEnv.txt was successful, import it
* If there is a uenvcmd variable (from uEnv.txt), run it
* Try to load uImage from the first FAT partition
* If it was successful, try to load da850-lego-ev3.dtb
* If loading uImage was successful, boot it (DT is optional)
* If none of the above was successful, try booting from flash

Suggested Flash Memory Layout
=============================

The following is based on the default U-Boot configuration:

| Image (file)       | Start Addr. | Max. Size         |
+--------------------+-------------+-------------------+
| u-boot.bin         |         0x0 |  0x40000 (256KiB) |
| da850-lego-ev3.dtb |     0x40000 |  0x10000 (64KiB)  |
| uImage             |     0x50000 | 0x400000 (4MiB)   |
| rootfs (squashfs)  |    0x450000 | 0xa00000 (10MiB)  |

Writing image to flash
======================

The EEPROM contains a program for uploading an image file to the flash memory.
The program is started by holding down the right button on the EV3 when powering
it on. You can also `run fwupdateboot` in the u-boot shell to reboot into this
mode. The image can then be uploaded using the official LEGO MINDSTORMS EV3
software or a 3rd party program capable of uploading a firmware file.

If you are booting from the microSD card, it is enough to just write uboot.bin
to the flash. If you are not using a microSD card, you will need to create an
image file using the layout described above.

IMPORTANT: The EEPROM bootloader only copies 256k, so u-boot.img must not
exceed that size!