[U-Boot] Boot based on I2C EEPROM value

[Detlev Zundel]

Hi Srivatsan,

> The modem I am working on contains two software images in flash memory:
>
> 1.	Default image
> 2.	Backup image
>
>  
>
> Typically, the Default image will get loaded. If the application
> software determines that the Default image is causing issues, it will
> set a value of 1 in an address in the I2C EEPROM and reboot the board.
>
>  
>
> So, U-boot will need to read this EEPROM value and determine whether it
> should boot the Default or Backup image i.e.
>
>  
>
> if EEPROM data == 0
>
>             bootm $default_addr
>
> else 
>
>             bootm $backup_addr
>
>  
>
> How can I read and parse the EEPROM data from U-boot? 
>
>  
>
> U-boot has the facility to read the I2C device from the command line as
> in (EEPROM dev num = 50, address = 2, count = 1):
>
> => i2c md 50 2 1
>
> 0002: 01    .
>
>  
>
> How do I parse this from within a U-boot command that can be run at
> boot-up?

Ah, this is interesting.  I was about to tell you to use the "standard"
i2c commands to transfer data from the chip into memory and then use the
hush shell and the standard "itest *addr = 1" facility.  Unfortunately,
the "i2c" subsystem does not implement such functionality.  So currently
I would advise to implement such "read" and "write" operations to
transfer to/from memory.

With this addition, you could even propose a patch to remove crc32
subcommand from i2c as this can then be done in two steps.  So maybe you
can even get away with this addition without adding anything to the
binary size of U-Boot ;)

Then itest would work like this:

=> md.b 0x200000 1
00200000: 00    .
=> if itest *0x200000 -eq 0 ; then echo zero;else echo not zero; fi
zero
=> mw.b 0x200000 1 1
=> md.b 0x200000 1                                                 
00200000: 01    .
=> if itest *0x200000 -eq 0 ; then echo zero;else echo not zero; fi
not zero
=> 

Cheers
  Detlev

-- 
An elephant is a mouse with an operating system.
                                        -- Donald Knuth
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