AR# 3657: MAP, PAR: Does Map or PAR insert global buffers on high fanout nets and/or unbuffered clock nets?
AR# 3657
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MAP, PAR: Does Map or PAR insert global buffers on high fanout nets and/or unbuffered clock nets?
描述
Keywords: insert, global buffer, map, par, fanout, clock, virtex, 4000ex
Urgency: standard
General Description: MAP, PAR: Does Map or PAR insert global buffers on high fanout nets and/or unbuffered clock nets?
解决方案
4000E/L: -------- No global buffer insertion
4000EX: ------- The router for 4000EX/XL/XV will use any available global buffer sites as routethrus for clock nets which are not already buffered. If additional global buffers are left over after all clock nets are allocated, they may also be inserted on high fanout nets.
The key element in the scoring is how many K pin loads are on the net. Because the placer and router share a common scoring object for this, the placer can locate the net's driver close to the selected global buffer site to minimize overall routing delays.
Virtex: ------- Virtex software will add global buffers to clock nets