Sistemi ad agenti Principi di programmazione di sistema

Transcript

Sistemi ad agenti
Principi di programmazione di sistema
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Modulo 6
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Why would anyone want to hack or write opensource project for
embedded system, when you already have a very powerful and
relatively cheap PC?
lower power
much more quiet
fast boot
sometimes more convenient to run certain applications on
these systems and not on a PC
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FOX Board LX
100MIPS, 1 Watt, Linux embedded board runs a real Linux
operating system in just 66 x 72 mm (2.6 x 2.8 inches).
The main field applications are:
Stand alone micro web servers
Macro component for OEM projects to reduce the design time
to build internet ready embedded devices.
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ST Microelectronics STB7109
Set-top-box (STB) decoder chip designed for low-cost
high-definition (HD) applications. It is based on 300MHz SH4-202
(ST40-202) CPU core with integrated MPEG video decoder, audio
decoder, Ethernet, SATA and USB 2.0 host controller.
STB7109E-REF (mb448) reference board also includes 2x64MB
DDR1 RAM (one DDR bank is used by the decoder and another
by the OS), 8MB flash and various video output interfaces,
including HDMI.
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Realtek 8186
The RTL8186/RTL8186P is a highly integrated System-on-a-Chip
with a high-performance 32-bit RISC micro-controller, two
Ethernet MACs, and a WLAN controller embedded onto a single
chip with a space-saving total package size of 17mm x 17mm. It is
a cost-effective solution for wireless LAN access points, wireless
SOHO routers, wireless multimedia appliance, etc.
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Software
Software stack typically consists of
”standard” embedded Linux (such as Das U-Boot) or vendor
proprietary bootloader
Linux kernel (uClinux in case of MMU-less processors)
uClibc library (as glibc memory requirements are not suited
for embedded systems)
busybox
a set of specific drivers and applications (es. mplayer,
iptables, ssh, gps drivers).
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Software cnt
Poky Linux http://www.pokylinux.org/
sdk Realtek
scratchbox http://www.scratchbox.org/
buildroot http://buildroot.uclibc.org/
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Embedded web servers
In the case of routers, access point and so on, the user interact
with the embedded system by a web server.
Popular embedded web server are Boa http://www.boa.org/
Goahead
http://www.goahead.com/products/webserver/default.aspx
microhttpd http://www.acme.com/software/micro httpd/
Embedded web server features are:
Small memory footprint
Strong support for dynamic generation of Web pages
Easy device integration
Support for devices without a file system
Portable to new platforms and CPU architectures
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Getting the shell prompt
The way is by serial port RS232 so you can:
to see all kinds of error messages, including kernel panic
to interact with the bootloader, which in some cases may be
the only way to program a new firmware image to flash.
Most embedded systems have UART controllers used for debug
and development.
UART pins are connected to a RS-232 interface through
a voltage level converter chip, which will translate logic UART
levels to the external RS-232 levels:
MAXIM (http://www.maxim-ic.com) MAX232.
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Getting the shell prompt: Minicom
On Windows: start> programmi > comunicazioni >
> accessori >HyperTerminal
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Trivial File Transfer Protocol
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Escape sequences to change cursor position
\033[<L>;<C>H to line L and column C
\033[<N>A down N lines
\033[<N>B up N lines
\033[<N>C forward N columns
\033[<N>D backward N columns
\033[s save position
\033[u resume position
Example: echo -en "\033[9A"
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Shell command to analyze source code and crosscompiler
look at 081007-devel.pdf http://www.gnudd.com/pub/srt-2008/
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Example: crosscompiling dropbear
wget http://matt.ucc.asn.au/dropbear/
/releases/dropbear-0.51.tar.bz2
tar xjf dropbear-0.51.tar.bz2
export USING_CROSS_COMPILER=y
export CROSS_COMPILER_PREFIX="mips-uclibc-"
export CC=mips-linux-uclibc-gcc-3.3.3
export STRIP=mips-linux-uclibc-strip
#use the following if you want statically compile
#export CFLAGS="-Os -static -Wall"
#export LDFLAGS="-static"
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Example: crosscompiling dropbear CNT
./configure CC=mips-linux-uclibc-gcc-3.3.3
--host=mips-linux-uclibc
--build=i686-linux CFLAGS=-O2
--disable-zlib --disable-lastlog --disable-largefile
make programs="dropbear dbclient dropbearkey
dropbearconvert scp" strip MULTI=1;
We have an unique binary a la busybox:
-rwxr-xr-x 1 root root 265K Dec 4 23:06 dropbearmulti
Project page: http://matt.ucc.asn.au/dropbear/dropbear.html
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Example: adding dropbear in the file system
cd $RAMFSDIR/dev/
ln -s urandom $RAMFSDIR/dev/random
mkdir -p $RAMFSDIR/etc/dropbear
cd ../../
cp ./dropbear-0.51/dropbearmulti
$RAMFSDIR/sbin/dropbearmulti
touch $RAMFSDIR/var/log/lastlog
touch $RAMFSDIR/var/log/wtmp
cd $RAMFSDIR/sbin
ln -s dropbearmulti $RAMFSDIR/sbin/dropbear
ln -s dropbearmulti $RAMFSDIR/sbin/scp
ln -s dropbearmulti $RAMFSDIR/sbin/dropbearkey
ln -s dropbearmulti $RAMFSDIR/sbin/dropbearconvert
ln -s dropbearmulti $RAMFSDIR/sbin/dbclient
ln -s dropbearmulti $RAMFSDIR/sbin/ssh
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Example: adding dropbear in the file system CNT
mips-linux-ldd dropbearmulti
libutil.so.0 => mips-linux-uclibc/lib/libutil.so.0 (0x00000000)
libcrypt.so.0 =>mips-linux-uclibc/lib/libcrypt.so.0 (0x00000000)
libc.so.0 => mips-linux-uclibc/lib/libc.so.0 (0x00000000)
/lib/ld-uClibc.so.0 => /lib/ld-uClibc.so.0 (0x00000000)
In the target file system:
cp $UCLIBCDIR/libcrypt-0.9.26.so $RAMFSDIR/lib/libcrypt.so.0
cp $UCLIBCDIR/libutil-0.9.26.so $RAMFSDIR/lib/libutil.so.0
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Example: starting ssh
/sbin/dropbearkey -t rsa
-f /etc/dropbear/dropbear_rsa_host_key
/sbin/dropbearkey -t dss
-f /etc/dropbear/dropbear_dss_host_key
OPTIONS="> /dev/null 2>&1"
echo "Stopping dropbear..."
pid=‘pidof dropbear‘
if [ "$pid" != "" ]; then
kill $pid
fi
echo "Starting dropbear..."
/sbin/dropbear $OPTIONS
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Example: testing ssh
On the WRT54G:
cat proc/net/tcp
DEMO
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Sistemi ad agenti Principi di programmazione di sistema

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