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The Bfv API Functions
November 2009 30
Channel Numbering
The Bfv API uses two numbering schemes when referencing
channels within a system. One is the unit number or ordinal channel
number; the other is the logical channel number.
The unit number is a number range 0…n-1, where n is the number of
channels in the system. The BfvLineAttach function uses the unit
number in its argument and returns a pointer to the BTLINE
structure, providing a means to reference the channel in future
function calls. For example, a system comprising two 60-channel
modules would have a unit number range of 0-119. The module that
had the firmware downloaded first would contain the channels
starting from 0.
The logical channel number is used together with the module
number to reference a work channel (also called a hardware channel)
in a system. The BfvSessionAttach function uses the module and
logical channel numbers in its arguments. Logical channels not only
include work channels traditionally considered to be channels, but
also administrative channels. The work channel number range for
logical channels is 2…n+1, where n is the number of work channels
on this hardware module.
Each module has a unique module number. For example, the same
system comprising two 60-channel modules could have the following
configuration:
First module: Module 2, work channels 2-61
Second module: Module 3, work channels 2-61
Each virtual module has 120 channels (the maximum allowed in a
system).
The BfvSessionAttach function also returns a BTLINE structure;
other functions that accept a BTLINE structure as an argument can
use either that returned from BfvLineAttach or
BfvSessionAttach. When detaching, use the corresponding detach
functions BfvLineDetach or BfvSessionDetach.
Unit numbers and BfvLineAttach are typical of our legacy product.