User manual

Linux Guide taskit GmbH
The parallel flash is connected to NSC0 and is used as the boot medium.
In the first phase of the boot process the Atmel controller starts the bootloader U-Boot.
The U-Boot start code loads the boot loader at address 21 F00 000 (SDRAM).
U-Boot then initializes the memory.
In the second phase of the boot process the bootloader boots the Linux image found in
flash memory.
The Linux image is decompressed to SDRAM. At last the root filesystem image is
decompressed by Linux and stored in SDRAM.
You can interrupt the boot process by pressing any key during the first phase of the boot
process (within 3 seconds). Then the U-Boot command line appears.
4.3. Reading and writing memory and flash memory
The AT91 data bus for memory is 32-bit and for flash 16-bit wide. Therefore, we
recommend using all variable memory commands with the .l, .w or .b option (long word,
word or byte). Otherwise, side effects cannot be ruled out.
Example:
cmp - memory compare
cmp [.l, .w, .b] Addr1 Addr2 count
You can check the contents of two memory ranges with the cmp command. Extensions
can be used to determine the size of the memory access:
cmp.l -> 32-bit long word (default), .w ->16-bit word or .b -> 8-bit byte.
The comparison runs until the number of units indicated by count have been compared, or
until the first difference is found. The size of the memory compared is calculated by count *
(l,w,b).
All commands that read memory can be used for both flash and SDRAM. Commands that
modify memory (with the exception of cp, which recognizes flash regions on its own) can
be used only for SDRAM and are inappropriate for directly writing flash memory.
Please note, when performing memory write operations, that the area containing the U-
Boot code is not modified; this will generally crash the system.
Before executing write operations on the flash memory you must ensure that the
corresponding memory range has already been erased, using the erase command
(described below). Note also that the memory area used for U-Boot and the environment
variables is protected against accidental write operations. You can turn this write
protection off and on using the protect command.
A complete list of all U-Boot commands can be found at the end of this document (chapter
U-Boot commands).
4.4. Scripts with U-Boot
Some environment variables are used by U-Boot if they are set, such as IP parameters.
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