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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