Ne vzdy je moznost provozovat ridici program primo na pocitaci se seriovym portem a pripojenym hardwarem. Prikladem jsou treba WiFi routery s OpenWrt. Do 4MB flash musite narvat system, ovladace i svoji aplikaci. Misto prepisovani programu do C a setreni mistem je casto pohodlnejsi seriovy port tunelovat na vykonny server.
Jak nasdilet seriovy port?
Jde to vice zpusoby, ale asi nejjednodussi je program ser2net. Ser2net ma po zakladni instalaci v konfiguraku /etc/ser2net.conf docela prehlednou dokumentaci:
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# # This is the configuration file for ser2net. It has the following format: # <tcp port="">:<state>:<timeout>:<device>:<options> # TCP port # Name or number of the TCP/IP port to accept con- # nections from for this device. A port number may # be of the form [host,]port, such as 127.0.0.1,2000 # or localhost,2000. If this is specified, it will # only bind to the IP address specified. Otherwise # it will bind to all the ports on the machine. # # state Either raw or rawlp or telnet or off. off disables # the port from accepting connections. It can be # turned on later from the control port. raw enables # the port and transfers all data as-is between the # port and the long. rawlp enables the port and # transfers all input data to device, device is open # without any termios setting. It allow to use # /dev/lpX devices and printers connected to them. # telnet enables the port and runs the telnet proto- # col on the port to set up telnet parameters. This # is most useful for using telnet. # # timeout # The time (in seconds) before the port will be dis- # connected if there is no activity on it. A zero # value disables this funciton. # # device The name of the device to connect to. This # must be in the form of /dev/<device>. # # options # Sets operational parameters for the serial port. # Options 300, 1200, 2400, 4800, 9600, 19200, 38400, # 57600, 115200 set the various baud rates. EVEN, # ODD, NONE set the parity. 1STOPBIT, 2STOPBITS set # the number of stop bits. 7DATABITS, 8DATABITS set # the number of data bits. [-]XONXOFF turns on (- # off) XON/XOFF support. [-]RTSCTS turns on (- off) # hardware flow control, [-]LOCAL turns off (- on) # monitoring of the modem lines, and # [-]HANGUP_WHEN_DONE turns on (- off) lowering the # modem control lines when the connextion is done. # NOBREAK disables automatic setting of the break # setting of the serial port. # The "remctl" option allow remote control (ala RFC # 2217) of serial-port configuration. A banner name # may also be specified, that banner will be printed # for the line. If no banner is given, then no # banner is printed. # # or... # BANNER:<banner name="">:banner # This will create a banner, if the banner name is given in the # options of a line, that banner will be printed. This takes the # standard "C" \x characters (\r is carraige return, \n is newline, # etc.). It also accepts \d, which prints the device name, \p, # which prints the TCP port number, and \s which prints the serial # parameters (eg 9600N81). Banners can span lines if the last # character on a line is '\'. Note that you *must* use \r\n to # start a new line. # # Note that the same device can be listed multiple times under different # ports, this allows the same serial port to have both telnet and raw # protocols. # The original config file shipped with the upstream sources can be # found in /usr/share/doc/ser2net/examples BANNER:banner:\r\nser2net port \p device \d [\s] (Debian GNU/Linux)\r\n\r\n 2000:telnet:600:/dev/ttyS0:9600 8DATABITS NONE 1STOPBIT banner 2001:telnet:600:/dev/ttyS1:9600 8DATABITS NONE 1STOPBIT banner 3000:telnet:600:/dev/ttyS0:19200 8DATABITS NONE 1STOPBIT banner 3001:telnet:600:/dev/ttyS1:19200 8DATABITS NONE 1STOPBIT banner</banner></device></options></device></timeout></state></tcp> |
Pro zacatek vsechno zakomentujeme. A hned potom zacneme pridavat vlastni radky.
Priklad (dale uvazujeme IP adresu serveru 192.168.1.1):
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3333:raw:60:/dev/ttyUSB0:9600 8DATABITS NONE 1STOPBIT # klasika... 4444:raw:60:/dev/ttyUSB1:115200 8DATABITS NONE 1STOPBIT # maximalni rychlost... 1234:raw:60:/dev/ttyS0:19200 8DATABITS NONE 2STOPBIT # 19200 8N2 - modbus rtu |
To budou jedine nezakomentovane radky v konfigu. Pote spustime ser2net.
Od teto chvile se PC chova jako server a po siti zpristupni seriove porty.
Na vytvoreni jednoho naslouchajici portu je mozne spustit ser2net primo z prikazove radky. Parametr -C definuje radek z konfiguracniho souboru:
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# <strong>ser2net -C "3333:raw:60:/dev/ttyUSB0:9600 8DATABITS NONE 1STOPBIT"</strong> |
Na OpenWrt je nutne nainstalovat ser2net a pokud pouzivame USB-RS232 prevodnik, tak i jeho ovladac:
# opkg update
# opkg install ser2net # + volitelne jmeno ovladace usb prevodniku
Seznam ovladacu prevodniku najdeme treba na http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/packages/base/
V prohlizeci si vyhledame „kmod-usb„.
Podpora prevodiku v aktualnim OpenWrt 14.07 je lepsi, nez v nejnovejsich Windows:
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kmod-usb-acm kmod-usb-serial-ark3116 kmod-usb-serial-belkin kmod-usb-serial-ch341 kmod-usb-serial-cp210x kmod-usb-serial-cypress-m8 kmod-usb-serial-ftdi kmod-usb-serial-ipw kmod-usb-serial-keyspan kmod-usb-serial-mct kmod-usb-serial-mos7720 kmod-usb-serial-motorola-phone kmod-usb-serial-option kmod-usb-serial-oti6858 kmod-usb-serial-pl2303 kmod-usb-serial-qualcomm kmod-usb-serial-sierrawireless kmod-usb-serial-ti-usb kmod-usb-serial-visor kmod-usb-serial-wwan kmod-usb-serial |
Pozor! OpenWrt pravdepodobne v dost verzich neresi automaticke spusteni ser2net po nabootovani. Je potreba zapnout init skript a pokud neexistuje, tak si ho napsat.
Ukazkovy init skript muze mit podobu treba:
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#!/bin/sh /etc/rc.common START=99 STOP=10 start() { ser2net } stop(){ killall ser2net sleep 1 # to je asi zbytecne killall -9 ser2net # to je asi zbytecne } |
ulozime ho do /etc/init.d/ser2net a zapneme:
# /etc/init.d/ser2net enable
Jak se k tomu pripojit?
Prvni a nejjednodussi moznosti je klasicky telnet. Muzeme pouzit PuTTY (Windowsaci), nebo klasicky telnet klient.
$ telnet 192.168.1.1 3333
nebo lepe
$ nc 192.168.1.1 3333
a muzeme psat. Vse se bude prenaset po siti az k zarizeni na RS-232. Vyuziti je skvele treba pri programovani. Nase naprogramovana aplikace si povida s hardwarem pres TCP socket a nic jineho ji nezajima. Pohodlne je to obzvlast u Javy. Vsichni, kdo ladili multipatformni Java aplikaci s RXTX knihovnou na seriovy port asi souhlasi…
Co kdyz ale potrebujeme mit „klasicky hardware“? Tedy bezny soubor zarizeni, ktery maji v linuxu vsechny seriove porty. K tomu se da pouzit program socat. Socat vytvori soubor zarizeni a data do/z nej sype pres TCP socket. Vse zcela transparentne. Uzivatel, ani aplikace nic nepoznaji:
# socat pty,link=/tmp/ttyV0,waitslave tcp:192.168.1.1:3333
# chmod 777 /tmp/ttyV0
Tim nam vzniklo nove zarizeni /tmp/ttyV0. Na praci je identicke s /dev/ttyS0. Klidne ho muzeme umistit do /dev, ale teoreticky se pak muze tlouct s jinym fyzicky pripojenym zarizenim. Pokud ma s nove vytvorenym zarizenim pracovat bezny uzivatel, je potreba nastavit zarizeni prava (777 neni vhodny priklad zabezpeceni). Ser2net-socat prenos neni sifrovany! Pokud potrebujeme sifrovat, muzeme komunikaci obalit treba stunellem.
Sam takhle tuneluji seriovy port z TP-Link WR741ND WiFi routeru s OpenWrt. K WiFi routeru je pres MAX485 (RS-485 sbernice) pripojene nekolik Arduino zarizeni. Protoze se ridici app do routeru nevesla (4MB flash neni moc), tak ovladani dela vzdaleny server.