Getting Started Boot from ROM Dynamic FLASH partitioning

The Linux kernel manages the on board FLASH through the standard MTD (Memory Technology Device) subsystem. Regardless the board type, by default, MTD divides the Flash into three partitions:

However, this layout can be customized. This can be useful, for example, on multi processor platforms like the Espresso to dedicate a FLASH region for the ST20 application (see the STi5528 Dual Boot chapter for more infos). Customized FLASH partitioning can be achieved in two ways:

1. temporary, at the kernel boot time using the argument mtdparts in the command line.
   The following example:

   ...mtdparts=Onboard_Flash:256k@0k,1024k@256k,2816k@1280k,-...

   will result in the following FLASH layout (see also the RAM layout example in the STi5528 Dual Boot page)
   

   Device	Size (KB)	Generally dedicate to...
   /dev/mtd0	256 Kb	Linux IPL program
   /dev/mtd1	1024 Kb	Compressed kernel image
   /dev/mtd2	2816 Kb	Root File System
   /dev/mtd3	remaining	...ST20 CPU...

   Onboard_Flash is a keyword used by the MTD device driver to distinguish between Flash on the main board and any other Flash on an optional STEM card. So it must be entered as exactly Onboard_Flash.

   Note - this method is simple but has few implications: when the kernel is launched from FLASH the IPL program must provide a a consistent command line, moreover when configuring the kernel, do not forget to enable the "Command line partition table parsing" in the "Memory Technology Device" section.

2. permanent, modifying the default FLASH partition defined by the structure "onboard_partitions" in the source file:

   .../drivers/mtd/maps/stboards.c

   This method doesn't impacts the IPL (unless the kernel start region is modified).

Device nodes to cover up to 16 FLASH slices are provided under /dev