[time-nuts] GPS Outage

[Magnus Danielson]

Hi Jim,

On 03/01/2016 03:24 PM, jimlux wrote:
> On 2/29/16 10:56 PM, Magnus Danielson wrote:
>>
>>
>> On 02/29/2016 11:31 AM, Martin Burnicki wrote:
>>> Hal,
>>>
>>> Hal Murray wrote:
>>>>
>>>> martin.burnicki at burnicki.net said:
>>>>>> Strange that at least 3 independant firmware trees/development
>>>>>> teams should
>>>>>> chose the same magic wk860.
>>>>
>>>>> I don't find it strange. If the next firmware version is based on the
>>>>> previous version and none of the developers has stumbled across this
>>>>> potential problem earlier ...
>>>>
>>>> That sounds like poor software engineering.  Or poor engineering
>>>> management.
>>>>
>>>> The wk860 is supposed to represent the build time of the software ...
>>>
>>> Do you *know* this, or are you just *assuming* this? ;-)
>>>
>>>> so it will
>>>> work for 20 years from when it was built rather than 20 years from
>>>> when the
>>>> 10 bit week counter last rolled over or 20 years from when the
>>>> constant was
>>>> last updated.
>>>
>>> There are also approaches where the proper extension of a week number
>>> doesn't just work within a single 1024 week cycle with some hardcoded
>>> limit, like this simple example:
>>>
>>> if ( wn < 860 )
>>>    wn += 1024;
>>>
>>> There may always be pieces of code which generate a faulty result under
>>> certain conditions, and no stumbles across this even in reviews until it
>>> really happens.
>>>
>>> I'm not aware of *any* project where each single line of code is checked
>>> once again whenever a new release is rolled out.
>>
>> Rather, in all projects I've seen there is a tendency to trust existing
>> code and only extend it. Re-validating it is usually regarded as money
>> in the sea. That old code can have incorrect assumptions that you
>> eventually expose as you change its environment is a re-occurring
>> learning experience.
>
>
> Ariane 5...

Indeed. Most of the cases the failure isn't as spectacular.

Cheers,
Magnus