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

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Message-ID: <5638F6EE.10505@hartkopp.net>
Date:	Tue, 03 Nov 2015 19:03:26 +0100
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	Marek Vasut <marex@...x.de>
CC:	Aleksander Morgado <aleksander@...ksander.es>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Vostrikov Andrey <andrey.vostrikov@...entembedded.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Andrew Lunn <andrew@...n.ch>
Subject: Re: [RFC][PATCH] net: arinc429: Add ARINC-429 stack

On 11/03/2015 06:41 PM, Marek Vasut wrote:
> On Tuesday, November 03, 2015 at 06:32:12 PM, Oliver Hartkopp wrote:
> 
> [...]
> 
>> It looks like you need to shift the stuff in user space every time.
>>
>> So you might better think of something like this:
>>
>>     struct a429_frame {
>>             __u32   label;   /* ARINC 429 label */
>>             __u8    length;  /* always set to 8 */
>>             __u8    __pad;   /* padding */
>>             __u8    __res0;  /* reserved / padding */
>>             __u8    __res1;  /* reserved / padding */
>>             __u32   data __attribute__((aligned(8)));
>>             __u8    p;       /* p */
>>             __u8    ssm;     /* ssm */
>>             __u8    sdi;     /* sdi */
>>             __u8    __end;   /* padding */
>>     };
> 
> You don't want to interpret those P(arity)/SSM/SDI bits, since they differ
> depending on whatever the remote party sends. That's why I decided to just
> make those into 3-bytes of data and let the userland application deal with
> it as seen fit. Besides, the ARINC "FTP" really uses those 3 bytes as plain
> data.

Ok. I did not know what P was for :-)

Btw. it can make sense to introduce an union struct where different options to
access the content are possible.

E.g. you might have a 32 bit word, some bit-wise specification and a four byte
tuple to access the three bytes for ARINC FTP ...

Regards,
Oliver

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