problem formulation:

objectives:

• performance: speed is everthing. why have cad tools if you have to wait all weekend for them to tell you something is wrong? i often trade memory usage for speed, it just seems like the right thing to do. given more time, i would work on some more balance, but in general its just much more fun to tweak for speed.
• functionality: okay, okay, its not really useful if it just creates a big ugly mess of wires - regardless of how fast it is. functionality is also important, sometimes even more important than performance. having the router do a good job was also really important.
• graphics: basically, graphics are cool. if youre going to write tools that do fun things. you might as well have interesting graphics to go with them. (of course, there are switches in the code to suppress graphics in deference to performance :)

plan of attack:

first thing to do is thing about data structures. its usually not easy to change a representation or concept after it is in code. usually works much better to think about it some before hand.

i was also a little liberal when deciding what data to store, ended up allocated some space for some things i wasnt sure i would use (there are a few things that could be trimmed from the data structures). again, its easier to trim things later than to have to hack things in.

the major data structures, like the heap and the hash table, were developed and tested independently of the router program. i dont like to have to develop an algorithm with buggy data structures. build with blocks that work so you know where the problems are when they occur.

for the graphics i made use of some code from another program i wrote. also spent some time tweaking things so that performance would not be affected too greatly by the graphics.

i would really liked to have implemented ripup and netlist pre-sorting, but there simply wasnt time. im still considering playing with the code when i find some free time.

tradeoffs:

• memory for performance
• performance for graphics
• ripup and net sort for time
• cells over capacity for all nets routed