Some tools are needed to install and configure U-Boot and Linux on
the target system. Also, especially during development, you will want
to be able to interact with the target system. This section describes
how to configure your host system for this purpose.
To use U-Boot and Linux as a development system and to make full use
of all their capabilities you will need access to a serial console
port on your target system. Later, U-Boot and Linux can be
configured to allow for automatic execution without any user
interaction.
There are several ways to access the serial console port on your target system,
such as using a terminal server, but the most common way is to attach it to a
serial port on your host. Additionally, you will need a terminal
emulation program on your host system, such as
cu or
kermit.
The
cu command is part of the
UUCP package and can be used to act as a dial-in
terminal. It can also do simple file transfers, which can be used in
U-Boot for image download.
On
RedHat systems you can check if the UUCP
package is installed as follows:
$ rpm -q uucp
If necessary, install the UUCP package from your distribution media.
To configure
cu for use with U-Boot and Linux
please make sure that the following entries are present in the
UUCP configuration files; depending on your target
configuration the serial port and/or the console baudrate may be
different from the values used in this example:
(
/dev/ttyS0, 115200 bps, 8N1):
#
# /dev/ttyS0 at 115200 bps:
#
system S0@115200
port serial0_115200
time any
#
# /dev/ttyS0 at 115200 bps:
#
port serial0_115200
type direct
device /dev/ttyS0
speed 115200
hardflow false
You can then connect to the serial line using the command
$ cu S0@115200
Connected.
To disconnect, type the escape character '~'
followed by '.' at the beginning of a line.
See also:
cu(1),
info uucp.
The name
kermit stands for a whole family of
communications software for serial and network connections. The fact
that it is available for most computers and operating systems makes
it especially well suited for our purposes.
kermit executes the commands in its
initialization file,
.kermrc, in your home
directory before it executes any other commands, so this can be
easily used to customize its behaviour using appropriate
initialization commands. The following settings are recommended for
use with U-Boot and Linux:
set line /dev/ttyS0
set speed 115200
set carrier-watch off
set handshake none
set flow-control none
robust
set file type bin
set file name lit
set rec pack 1000
set send pack 1000
set window 5
This example assumes that you use the first serial port of your host
system (
/dev/ttyS0) at a baudrate of
115200 to connect to the target's serial console port.
You can then connect to the serial line:
$ kermit -c
Connecting to /dev/ttyS0, speed 115200.
The escape character is Ctrl-\ (ASCII 28, FS)
Type the escape character followed by C to get back,
or followed by ? to see other options.
----------------------------------------------------
Due to licensing conditions you will often find two kermit packages
in your GNU/Linux distribution. In this case you will want to install the
ckermit package. The
gkermit package is only a command line
tool implementing the kermit transfer protocol.
If you cannot find
kermit on the distribution
media for your Linux host system, you can download it from
the kermit project home page:
http://www.columbia.edu/kermit/
minicom is another popular serial communication
program. Unfortunately, many users have reported problems using it
with U-Boot and Linux, especially when trying to use it for serial
image download. It's use is therefore discouraged.
The terminal emulation program must have write access to the serial
port and to any locking files that are used to prevent concurrent
access from other applications. Depending on the used Linux
distribution you may have to make sure that:
- the serial device belongs to the same group as the
cu command, and that the permissions of
cu have the setgid bit set
- the
kermit belongs to the same group as
cu and has the setgid bit set
- the /var/lock directory
belongs to the same group as the
cu command, and
that the write permissions for the group are set
The fastest way to use U-Boot to load a Linux kernel or an
application image is file transfer over Ethernet. For this purpose,
U-Boot implements the
TFTP protocol (see the
tftpboot command in U-Boot).
To enable
TFTP support on your host system you must make sure that
the
TFTP daemon program
/usr/sbin/in.tftpd is
installed. On
RedHat systems you can verify this by running:
$ rpm -q tftp-server
If necessary, install the
TFTP daemon program from your distribution media.
Most Linux distributions disable the
TFTP service by default. To
enable it for example on
RedHat systems, edit the file
/etc/xinetd.d/tftp and
remove the line
disable = yes
or change it into a comment line by putting a hash character in front of
it:
# default: off
# description: The tftp server serves files using the trivial file transfer
# protocol. The tftp protocol is often used to boot diskless
# workstations, download configuration files to network-aware printers,
# and to start the installation process for some operating systems.
service tftp
{
socket_type = dgram
protocol = udp
wait = yes
user = root
server = /usr/sbin/in.tftpd
server_args = -s /tftpboot
# disable = yes
per_source = 11
cps = 100 2
}
Also, make sure that the
/tftpboot directory exists and
is world-readable (permissions at least "dr-xr-xr-x").
On newer Linux distros that use systemd, you would need to start the
TFTP service, enable it, then tweak your firewall to allow
TFTP traffic, something like this:
$ sudo systemctl start tftp
$ sudo systemctl enable tftp
$ sudo firewall-cmd --permanent --add-service tftp
$ sudo firewall-cmd --reload
BOOTP resp.
DHCP can be used to
automatically pass configuration information to the
target. The only thing the target must "know" about itself is its own
Ethernet hardware (
MAC) address. The following command can be used to check if
DHCP support is available on your host system:
$ rpm -q dhcp
If necessary, install the
DHCP package from your distribution
media.
Then you have to create the
DHCP configuration file
/etc/dhcpd.conf that matches your network setup.
The following example gives you an idea what to do:
subnet 192.168.0.0 netmask 255.255.0.0 {
option routers 192.168.1.1;
option subnet-mask 255.255.0.0;
option domain-name "local.net";
option domain-name-servers ns.local.net;
host trgt { hardware ethernet 00:30:BF:01:02:D0;
fixed-address 192.168.100.6;
option root-path "/opt/eldk-4.2/ppc_4xx";
option host-name "canyonlands";
next-server 192.168.1.1;
filename "/tftpboot/canyonlands/uImage";
}
}
With this configuration, the
DHCP server will reply to a request from
the target with the ethernet address
00:30:BF:01:02:D0 with the following information:
- The target is located in the subnet
192.168.0.0
which uses the netmask 255.255.0.0.
- The target has the hostname
canyonlands
and the IP address 192.168.100.6.
- The host with the IP address
192.168.1.1 will
provide the boot image for the target and provide NFS server
function in cases when the target mounts it's root filesystem over
NFS.
The host listed with the next-server
option can be different from the host that is running the DHCP
server.
- The host provides the file /tftpboot/canyonlands/uImage
as boot image for the target.
- The target can mount the directory
/opt/eldk-4.2/ppc_4xx on the NFS
server as root filesystem.
For a development environment it is very convenient when the host and
the target can share the same files over the network. The easiest way for
such a setup is when the host provides NFS server functionality and
exports a directory that can be mounted from the target as the root
filesystem.
Assuming NFS server functionality is already provided by your host, the
only configuration that needs to be added is an entry for your target
root directory to your
/etc/exports file, for
instance like this:
/opt/eldk-4.2/ppc_4xx 192.168.0.0/255.255.0.0(rw,no_root_squash,sync)
This line exports the
/opt/eldk-4.2/ppc_4xx directory
with read and write permissions to all hosts on the
192.168.0.0
subnet.
After modifying the
/etc/exports file you must
make sure the NFS system is notified about the change, for instance
by issuing the command:
# /sbin/service nfs restart
