Abstract
The use of programmable logic cells in VLSI design allows the terminals on these cells to be interchanged since
their geometrics are programmable. Recently, many exact algorithms and heuristics have been proposed for
channel routing with interchangeable terminals [18, 25, 4, 11, 12, 20, 17, 3]. Various optimization problems have
also been shown to be NP—hard [25, 23]. In this paper, we consider channels with exits. Let m, D be the number
of terminals in the channel and the maximum number of terminals on a net, respectively. We present an O(m)
algorithm that obtains optimal density for channels with exits that have one cell on each side. The existing
algorithm for this problem [5] guarantees only an approximate density. Moreover, if one of the two cells has
fixed terminals, we show that the density minimization problem is NP-hard. The latter problem was introduced
in [5]. For instances with any number of cells we present an O(m) time algorithm for the via minimization problem,
an O(