LinuxInFlash < DULG

%SECTION0{name=LinuxInFlash}% Boot from Flash Memory

The previous section described how to load the Linux kernel image
over ethernet using TFTP. This is especially well suited for your
development and test environment, when the kernel image is still
undergoing frequent changes, for instance because you are modifying
kernel code or configuration.

Later in your development cycle you will work on application code or
device drivers, which can be loaded dynamically as modules. If the
Linux kernel remains the same then you can save the time needed for
the TFTP download and put the kernel image into the flash memory of
your %BOARDNAME% board.

The U-Boot command =flinfo= can be used to display
information about the available on-board flash on your system:

%INCLUDE{DULGData_%BOARD%.UBootFlinfo}%

From this output you can see the total amount of flash memory, and
how it is divided in blocks (_Erase Units_ or
_Sectors_). The =RO= markers
show blocks of flash memory that are write protected (by software) -
this is the area where U-Boot is stored. The remaining flash memory
is available for other use.

For instance, we can store the Linux kernel image in flash starting
at the start address of the next free flash sector. Before we can do
this we must make sure that the flash memory in that region is empty
- a Linux kernel image is typically around 600...700 kB, so to be on
the safe side we dedicate the whole area from 0x%KERNEL_ADDR% to
0x%KERNEL_END% for the kernel image. Keep in mind that with
flash memory only whole erase units can be cleared.

After having deleted the target flash area, you can download
the Linux image and write it to flash.  Below is a transcript of
the complete operation with a final =iminfo= command to check
the newly placed Linux kernel image in the flash memory.

%INCLUDE{DULGData_%BOARD%.InstallKernelTftp}%

Note how the =filesize= variable (which gets set by
the TFTP transfer) is used to automatically adjust for the actual
image size.

%IF{ "%ARCH%" eq "powerpc"}%
Since kernel requires the flattened device tree blob to be passed at boot time, you have to also write the blob to the flash memory. Below is a transcript of this operation.
%INCLUDE{DULGData_%BOARD%.InstallBlobTftp}%
%ENDIF% 

Now we can boot directly from flash. All we need to do is passing the
in-flash address of the image (%KERNEL_ADDR%) %IF{ "%ARCH%" eq "powerpc"}%
and the in-flash address of the flattened device tree (%FDT_ADDR%) %ENDIF% with the =bootm=
command; we also make the definition of the
=bootargs= variable permanent now:

<pre>
%UBOOT_PROMPT% setenv bootcmd bootm %KERNEL_ADDR% %IF{ "%ARCH%" eq "powerpc"}% - %FDT_ADDR% %ENDIF%
%UBOOT_PROMPT% setenv bootargs root=/dev/nfs rw nfsroot=${serverip}:${rootpath} ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}::off
</pre>

Use =printenv= to verify that everything is OK before you save the
environment settings:

<pre>
%UBOOT_PROMPT% printenv
bootdelay=5
baudrate=%CONSOLE_BAUDRATE%
stdin=serial
stdout=serial
stderr=serial
bootcmd=bootm %KERNEL_ADDR% %IF{ "%ARCH%" eq "powerpc"}% - %FDT_ADDR% %ENDIF%
bootargs=root=/dev/nfs rw nfsroot=%SERVERIP%:%ROOTPATH%
ip=%IPADDR%:%SERVERIP%:%GATEWAYIP%:%NETMASK%:%HOSTNAME%::off
....

%UBOOT_PROMPT% saveenv
</pre>

To test booting from flash you can now reset the board (either by
power-cycling it, or using the U-Boot command
=reset=), or you can manually call the
=boot= command which will run the commands in the
=bootcmd= variable:

%INCLUDE{"DULGData_%BOARD%.LinuxBootSelf"}%
7.5. Networked Operation with Root Filesystem over NFS		1. Abstract		7.7. Standalone Operation with Ramdisk Image
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