U-Boot for the Gateworks Ventana Product Family boards

This file contains information for the port of U-Boot to the Gateworks
Ventana Product family boards.

1. Secondary Program Loader (SPL)
---------------------------------

The i.MX6 has a BOOT ROM PPL (Primary Program Loader) which supports loading
an executable image from various boot devices.

The Gateworks Ventana board config uses an SPL build configuration. This
will build the following artifacts from u-boot source:
 - SPL - Secondary Program Loader that the i.MX6 BOOT ROM (Primary Program
         Loader) boots.  This detects CPU/DRAM configuration, configures
         The DRAM controller, loads u-boot.img from the detected boot device,
         and jumps to it.  As this is booted from the PPL, it has an IVT/DCD
         table.
 - u-boot.img - The main u-boot core which is u-boot.bin with a image header.


2. Build
--------

To build U-Boot for the Gateworks Ventana product family:

 make gwventana_config
 make


3. Boot source, boot from NAND
------------------------------

The i.MX6 BOOT ROM expects some structures that provide details of NAND layout
and bad block information (referred to as 'bootstreams') which are replicated
multiple times in NAND. The number of replications and their spacing (referred
to as search stride) is configurable through board strapping options and/or
eFUSE settings (BOOT_SEARCH_COUNT / Pages in block from BOOT_CFG2). In
addition, the i.MX6 BOOT ROM Flash Configuration Block (FCB) supports two
copies of a bootloader in flash in the case that a bad block has corrupted one.
The Freescale 'kobs-ng' application from the Freescale LTIB BSP, which runs
under Linux and operates on an MTD partition, must be used to program the
bootstream in order to setup this flash structure correctly.

The Gateworks Ventana boards with NAND flash have been factory programmed
such that their eFUSE settings expect 2 copies of the boostream (this is
specified by providing kobs-ng with the --search_exponent=1 argument). Once in
Linux with MTD support for the NAND on /dev/mtd0 you can program the SPL
with:

kobs-ng init -v -x --search_exponent=1 SPL

The kobs-ng application uses an imximage which contains the Image Vector Table
(IVT) and Device Configuration Data (DCD) structures that the i.MX6 BOOT ROM
requires to boot.  The kobs-ng adds the Firmware Configuration Block (FCB) and
Discovered Bad Block Table (DBBT).  The SPL build artifact from u-boot is
an imximage.

The u-boot.img, which is the non SPL u-boot binary appended to a u-boot image
header must be programmed in the NAND flash boot device at an offset hard
coded in the SPL. For the Ventana boards, this has been chosen to be 14MB.
The image can be programmed from either u-boot or Linux:

u-boot:
Ventana > setenv mtdparts mtdparts=nand:14m(spl),2m(uboot),1m(env),-(rootfs)
Ventana > tftp ${loadaddr} u-boot.img && nand erase.part uboot && \
          nand write ${loadaddr} uboot ${filesize}

Linux:
nandwrite /dev/mtd1 u-boot.img

The above assumes the default Ventana partitioning scheme which is configured
via the mtdparts env var:
 - spl: 14MB
 - uboot: 2M
 - env: 1M
 - rootfs: the rest

This information is taken from:
  http://trac.gateworks.com/wiki/ventana/bootloader#NANDFLASH

More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.