7
5
Software features
As provided by Boundary Devices, the Nitrogen
R
board supports either the Windows CE 6
R
or
Linux operating systems. There are currently two shipping versions of Linux:
1.
Busybox
- A small Linux userland, and
2.
Ubuntu
- A full-featured X-Windows based installation
To simplify the installation of either, the
U-Boot
boot loader is installed on our evaluation boards,
and one or more
MMC
cards are shipped to allow the use of either operating system.
5.1
Internal ROM boot loader and boot flow
The i.MX51 processor contains an internal boot loader in ROM that supports boot from serial
EEPROM, SD card, USB, NAND or NOR flash.
Freescale
has a number of documents about how
this process is done. In this document, we’ll describe how the demonstration images are currently
configured.
To begin with, the Nitrogen
R
is configured to boot from SD card. As shown in figure 3, the
internal ROM loads code from offset 0x400 (1k) and executes it. Note that this first set of code is
placed in non file-system area, so it must be loaded to disk using a tool such as
dd
under Linux.
The current incarnation of
U-Boot
then loads its’ environment settings from offset 0x1c00 (block
14) of the SD card. This is also in space before the first partition.
The next steps depend primarily on the values found in the environment, especially the
bootcmd
variable.
Note that future iterations of the Nitrogen
R
will likely place both
U-Boot
and the environment
variable in serial EEPROM.
5.2
Das U-Boot
The
U-Boot
Boot Loader is a full-featured loader for either Linux or Windows CE that supports a
wide variety of options for loading your Operating System and application.
The
U-Boot
Boot Loader is a very capable loader with support for USB and network boot, including
BOOTP/DHCP, and NFS mounting support.
Please refer to the
U-Boot
website for details of the operation. The sections which follow will
describe typical usage for various operating systems and variants.
In general, though, our O/S releases will have the following features.
Serial console
Releases from Boundary Devices will be configured to allow access to the U-Boot
command-line on the primary serial port
1
with a baud rate of
115200
, no parity, 8 data bits. They’ll
be configured to stop the boot process on any input character on the console.
bootcmd
in persistent environment
1
COM1:
under CE,
/dev/ttymxc0
under Linux
March 10, 2011
Revision 1.5