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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.
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