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Subject: Re: [PATCH v10 0/7] Add Fieldbus subsystem + support HMS Profinet
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From:   "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Organization: metux IT consult
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Date:   Wed, 17 Apr 2019 22:13:59 +0200
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On 17.04.19 19:04, Andreas Färber wrote:

Hi,

> If you see specific conflicts or differences, please explain them> instead of just throwing around bus names. :) Then we can more easily>
discuss whether to make changes to this framework or whether we indeed>
need some fieldbus/iec61158/ subdirectory.

For example, MVB semantically is more similar to can/canopen or even
SNMP than to iec61158. T-bus is logically more a typically network
interface (similar to 802.3 or HDLC), WTB is actually HDCL via RS485.
KNX has similarities to canopen or SNMP. DALI is somewhat similar
to I2C.

Ergo: there're various fieldbus protocols with entirely different
concepts. Distributed process memory like in iec61158 is just one
of them.

> For your RS-485 I don't see > conflict as that'll just go via tty/serial/ and optionally serdev, no?

That's just layer 0/1. Ontop of that there're various protocols.
Some folks do some ASCII-based protocol ontop of that (eg. elevators,
water plants, etc), others put in HDLC (eg. WTB), some do completely
weird things ;-)

> However, I'd be curious how I/O Link might relate to this, it seems to> have no public specifications.
https://io-link.com/de/Download/Download.php
https://io-link.com/share/Downloads/Spec-Interface/IOL-Interface-Spec_10002_V112_Jul13.pdf

> While I do like sockets, they seem more useful for packet-based> communication, which may be an implementation detail of fieldbus_dev>
drivers, but AFAIU that's unrelated to Sven's memory-focused subsystem>
representing a view of the data received, which may be different from>
the last packet received. Also, when a packet is received via socket,
it> gets dequeued, whereas you'll want to access the device's memory
without> restrictions.
okay, if the device always represents the current process memory, w/o
showing the actual communication, then Sven's approach makes sense.


--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@metux.net -- +49-151-27565287