u-boot/doc/README.imx6

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.

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