Pickering Card Topology
- This discussion is most pertinent to the low level drivers from Pickering: pipx40, pilpxi and piplx where the objective is the control of switch entities.
- The IVI driver pi40iv operates using a different paradigm of the routing between end points, some of this discussion is less relevant to that driver.
Pickering cards contain multiple switches (or other functionality) usually organised into functional groups, for example a multiplex or a matrix.
The firmware of a Pickering card presents the contained switches in such logical groups. We use the term 'subunit' to describe such a logical grouping.
So, to control a switch the user must know in which subunit that switch resides.
In many cases a card will contain just a single subunit; in other cases there may be many subunits. If there is any doubt, refer to the specific product manual for details of the subunit structure.
Each subunit in the driver interface contains a number of bits, one per switch, contained in one or more 32-bit words.
The driver provides functions to allow the control a single bit or the control of all bits in a single operation.
Each function will therefore need information about the card and the subunit followed by information about the particular switch or switches to be controlled.