netdev - Re: [RFC][PATCH] net: arinc429: Add ARINC-429 stack

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Date:	Mon, 02 Nov 2015 12:14:27 +0100
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	Marc Kleine-Budde <mkl@...gutronix.de>,
	Marek Vasut <marex@...x.de>, netdev@...r.kernel.org
CC:	"David S. Miller" <davem@...emloft.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Andrew Lunn <andrew@...n.ch>,
	Andrey Vostrikov <andrey.vostrikov@...entembedded.com>
Subject: Re: [RFC][PATCH] net: arinc429: Add ARINC-429 stack

On 02.11.2015 10:47, Marc Kleine-Budde wrote:
> On 11/02/2015 12:16 AM, Marek Vasut wrote:
>> The ARINC-429 is a technical standard, which describes, among others,
>> a data bus used by airplanes. The standard contains much more, since
>> it is based off the ISO/OSI model, but this patch implements just the
>> data bus protocol.
>>
>> This stack is derived from the SocketCAN implementation, already present
>> in the kernel and thus behaves in a very similar fashion. Thus far, we
>> support sending RAW ARINC-429 datagrams, configuration of the RX and TX
>> clock speed and filtering.
>>
>> The ARINC-429 datagram is four-byte long. The first byte is always the
>> LABEL, the function of remaining three bytes can vary, so we handle it
>> as an opaque PAYLOAD. The userspace tools can send these datagrams via
>> a standard socket.
>>
>> A LABEL-based filtering can be configured on each socket separately in
>> a way comparable to CAN -- user uses setsockopt() to push a list of
>> label,mask tuples into the kernel and the kernel will deliver a datagram
>> to the socket if (<received_label> & mask) == (label & mask), otherwise
>> the datagram is not delivered.
>
> What's difference compared to CAN besides a different MTU? The CAN stack
> is already capable to handle CAN and CAN-FD frames. Would it make sense
> to integrate the ARINC-429 into the existing CAN stack?

That was my first impression too.

What about defining some overlay data structure to map ARINC-429 frames into 
CAN frames?

E.g. we could write the ARINC 32 bit data completely into data[0..3] and 
additionally copy the 8 bit label information (or should it better be 10 bit 
including the Source/Destination Identifiers?) additionally into the can_id.

 From what I can see the filtering by label is similar to filtering by can_id.
And you would be able to use the can-gw functionality too.

The only real difference is the bitrate configuration of the ARINC interface.

I wonder if a similar approach would fit here as we discussed with the 
University of Prague for a LIN implementation using the PF_CAN infrastructure:

http://rtime.felk.cvut.cz/can/lin-bus/

It could probably boil down to a 'CAN interface' that is named arinc0 which 
implements the serial driver like in slcan.c or sllin.c ...

Regards,
Oliver

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