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| − | ZBus is a [[wikipedia:RS485|RS485]] based two wire bus, which transmits IP packages.
| + | #REDIRECT[[:Kategorie:ZBus]] |
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| − | == ZBus Interface ==
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| − | ZBus is designed to transfer packets between embedded devices, for example
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| − | microcontrollers like the ATmega8 and the ATmega644. Within ethersex it is
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| − | used to transfer raw IP packets from an ethernet-zbus-bridge to the zbus
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| − | devices.
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| − | Ethersex can also be compiled for smaller ATmegas, like the ATmega8. In this
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| − | case you normally don't attach a [[ENC28J60]] to the
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| − | little IC. Instead you can add a RS485
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| − | driver IC. Over this serial line all the communication will be done. In the
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| − | small ATmega8 a whole IPv4 ( or IPv6 ) stack is installed and it processes the
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| − | data, which comes over the serial line. The stack will be able to process ICMP
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| − | and UDP, but TCP is not possible with this amount of RAM.
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| − | The interface between the ZBus "net" and the normal LAN is a biggger ATmega
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| − | (e.g. ATmega644) with both, a ethernet driver and a RS485 driver. For more
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| − | informations about the zbus bridges look see [[Network Briges]]. It can also be a normal computer with a serial interface and [[#Serial Host|Zbus Serial Host]] running on it.
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| − | == ZBus Protocol ==
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| − | ZBus is a protocol to transfer packets over an serial line, where only one
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| − | byte can be sent at once, e.g. RS485. The problem with such a serial line is,
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| − | that every byte is independend from another byte. So you have to define a
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| − | format for a packets, in which you can chain many bytes together, in
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| − | order send more information than just one byte. ZBus is such an format.
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| − | ZBus is a little bit related to [[I2C]]: There is an start condtition at the
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| − | beginning of a packet and a stop conditon at the end. Between start and
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| − | stop condtiontion is no field that represents the length of the packet.
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| − | The start condtiotion is an '\' (0x5C) followed by an '0' (0x30).
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| − | Corresponding to that is the stop condition an '\' (0x5C) followed by an
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| − | '1' (0x31). But we also have to escape all '\' (0x5C) inside the packet,
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| − | so that an start condtiotion can't be happen at random. ZBus does this in
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| − | the normal Unix way by replacing every '\' with an '\\'
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| − | A packet can for example look like this:
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| − | \0get information about \\0 and \\1 in zbus\1
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| − | The plain message whoul be:
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| − | get information about \0 and \1 in zbus
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| − | == Hardware ==
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| − | The only thing you need to extend an ATmega* with ZBus is a RS485 IC (e.g. MAX485). A example how the IC is attached to the single ATmegas is at [[Media:Zbus.pdf]]
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| − | == Serial Host ==
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| − | Because ZBus is based on the Usart feature, with have almost all ATmegas, we can simply attach an ZBus network interface to our computer.
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| − | The serial interface (aka COM-Port, aka R232) is only an normal usart with signal level converter ( -3V - +15V ). In order to make a RS485 interface, which is needed for ZBus, you will have to attach a MAX232 ( or similar ), to convert the RS232 signal back to an Usart TTL signal, and a RS485 interface chip to create the differential signal.
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| − | Some embedded device have some usarts on board, which are not soldered to a signal converter, so they provide the Usart TTL signal directly. You must only attach the RS485 chip and compile the driver for the architecture. The Linksys WRT54G is such an embedded device with an unsoldered Usart on board.
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| − | On the software side, i decided to write an userland driver with tun devices instead of writing a kernel module, because it is much more simpler to code and to debug. The programm provides an usual network interface, like your normal ethernet card, and can also be used like it (e.g. routing, different IP addresses and so on ). So you are very fexible with it. You can find the driver daemon in the contrib/zbus-serial-host, within the normal EtherSex repository.
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| − | <pre>
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| − | zbus0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
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| − | inet addr:192.168.9.1 P-t-P:192.168.9.1 Mask:255.255.255.0
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| − | UP POINTOPOINT RUNNING NOARP MULTICAST MTU:174 Metric:1
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| − | RX packets:16418 errors:0 dropped:0 overruns:0 frame:0
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| − | TX packets:16423 errors:0 dropped:0 overruns:0 carrier:0
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| − | collisions:0 txqueuelen:500
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| − | RX bytes:1381934 (1.3 MiB) TX bytes:1379532 (1.3 MiB)
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| − | </pre>
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| − | An open source rs232 to rs485 converter you can be found at [[RS485 Converter]].
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| − | == ZBus Bootloader ==
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| − | We have also written a [[http://git.brokenpipe.de/cgi-bin/gitweb.cgi?p=bricolage/zbusloader;a=summary small bootloader]] which is able to flash your devices (at the moment only ATmega8 is supported) over the ZBus line. It fits into
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| − | 512 bytes of flash. You have to enable zbus_raw on your ethernet-zbus bridge,
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| − | because the zbusloader doesn't use IP packets to communicate with the
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| − | bootloader, but raw ZBus packets. You can find more informations in the zbusloader [[http://git.brokenpipe.de/cgi-bin/gitweb.cgi?p=bricolage/zbusloader;a=blob;f=README;hb=master README]]
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| − | === Code ===
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| − | git clone http://brokenpipe.de/gitroot/bricolage/zbusloader
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| − | [[Category:ethersex]]
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