Shared Area Addressing - Add/Substrack 8

[TomekP]

Hello,

I'm trying to understand Shared Area Addressing - actually how  Port Index is written in AreaID

Now I have found the equasion stating:

Port number in dec = Area ID in Hex + Node Address in Hex - 8 in Hex

Which is very often true, but sometimes it is +8 in Hex.

Best example:

Port Index   --------    PID

279 --------      0a9f80
280--------       0a9080

279 = 0x9f + 0x80 - 0x8 = 159 + 128 - 8 = 279 

280 = 0x90 + 0x80 + 0x8 = 144 + 128 + 8 = 280

I have no idea how it works.

[sebastian.thaele]

Honestly, why is that even important? Looking into switchshow will give you the proper port. In my eyes the whole concept is ... let's say I think nobody is proud of it. For example if you have 64-port blades it's 40 and C0 in addition. And as soon as you change the format, all calculation is void anyway. IMHO guessing the port number from the PID is a thing of the past.

[TomekP]

thanks Sebastian. Although I'm learning for the exam and I believe this will not be acceptable answer :)

Plus i would really like to understand that. it's not about 'guessing the port number from PID', more like understand how that works.

cheers