U-Boot for Freescale i.MX6

This file contains information for the port of U-Boot to the Freescale i.MX6
SoC.

1. CONVENTIONS FOR FUSE ASSIGNMENTS
-----------------------------------

1.1 MAC Address: It is stored in fuse bank 4, with the 32 lsbs in word 2 and the
    16 msbs in word 3[15:0].
    For i.MX6SX and i.MX6UL, they have two MAC addresses. The second MAC address
    is stored in fuse bank 4, with the 16 lsb in word 3[31:16] and the 32 msbs in 
    word 4.

Example:

For reading the MAC address fuses on a MX6Q:

- The MAC address is stored in two fuse addresses (the fuse addresses are
described in the Fusemap Descriptions table from the mx6q Reference Manual):

0x620[31:0] - MAC_ADDR[31:0]
0x630[15:0] - MAC_ADDR[47:32]

In order to use the fuse API, we need to pass the bank and word values, which
are calculated as below:

Fuse address for the lower MAC address: 0x620
Base address for the fuses: 0x400

(0x620 - 0x400)/0x10 = 0x22 = 34 decimal

As the fuses are arranged in banks of 8 words:

34 / 8 = 4 and the remainder is 2, so in this case:

bank = 4
word = 2

And the U-Boot command would be:

=> fuse read 4 2
Reading bank 4:

Word 0x00000002: 9f027772

Doing the same for the upper MAC address:

Fuse address for the upper MAC address: 0x630
Base address for the fuses: 0x400

(0x630 - 0x400)/0x10 = 0x23 = 35 decimal

As the fuses are arranged in banks of 8 words:

35 / 8 = 4 and the remainder is 3, so in this case:

bank = 4
word = 3

And the U-Boot command would be:

=> fuse read 4 3
Reading bank 4:

Word 0x00000003: 00000004

,which matches the ethaddr value:
=> echo ${ethaddr}
00:04:9f:02:77:72

Some other useful hints:

- The 'bank' and 'word' numbers can be easily obtained from the mx6 Reference
Manual. For the mx6quad case, please check the "46.5 OCOTP Memory Map/Register
Definition" from the "i.MX 6Dual/6Quad Applications Processor Reference Manual,
Rev. 1, 04/2013" document. For example, for the MAC fuses we have:

Address:
21B_C620	Value of OTP Bank4 Word2 (MAC Address)(OCOTP_MAC0)

21B_C630	Value of OTP Bank4 Word3 (MAC Address)(OCOTP_MAC1)

- The command '=> fuse read 4 2 2' reads the whole MAC addresses at once:

=> fuse read 4 2 2
Reading bank 4:

Word 0x00000002: 9f027772 00000004

2. Using imx_usb_loader for first install with SPL
--------------------------------------------------

imx_usb_loader is a very nice tool by BoundaryDevice that
allow to install U-Boot without a JTAG debugger, using
the USB boot mode as described in the manual. It is
a replacement for Freescale's MFGTOOLS.

The sources can be found here:

	https://github.com/boundarydevices/imx_usb_loader.git

Booting in USB mode, the i.MX6 announces itself to the Linux Host as:

Bus 001 Device 111: ID 15a2:0061 Freescale Semiconductor, Inc.

imx_usb_loader is able to download a single file (u-boot.imx)
to the board. For boards without SPL support, it is enough to
issue the command:

	sudo ../imx_usb_loader/imx_usb -v u-boot.imx

Getting U-Boot when SPL support is active, it requires
two downloads. imx_usb_loader downloads the SPL into
OCRAM and starts it. SPL will check for a valid u-boot.img, and
because it is not found, it will wait for it using the y-modem
protocol via the console.

A first install is then possible by combining imx_usb_loader with
another tool such as kermit.

sudo ../imx_usb_loader/imx_usb -v SPL
kermit kermit_uboot

and kermit_uboot contains something like this (set line should be adjusted):

set line /dev/ttyUSB1
set speed 115200
SET CARRIER-WATCH OFF
set flow-control none
set handshake none
set prefixing all
set file type bin
set protocol ymodem
send u-boot.img
c

The last "c" command tells kermit (from ckermit package in most distros)
to switch from command line mode to communication mode, and when the
script is finished, the U-Boot prompt is shown in the same shell.