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FPGA-Research-Manchester / FABulous

Fabric generator and CAD tools
https://fabulous.readthedocs.io/en/latest/
Apache License 2.0
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What do NN, EE, SS and WW stand for? #139

Closed IAmMarcelJung closed 8 months ago

IAmMarcelJung commented 11 months ago

In the documentation, the naming scheme for source_name and destination_name of a wire is explained. According to the definition, for a wire named e.g. NxBeg, x should reflect how far the wire is routed, with x ∈ {1,2,4,6}. However, in fabric.csv, x can also be N, E, S or W, depending on the direction, so a wire can have e.g. the name NNBeg. I could not find a definition for this type of wire in the definition.

Can anybody tell me what it stands for or point me to where it is explained in the documentation, if it is explained there?

Thanks in advance!

IAmMarcelJung commented 11 months ago

I have to somewhat correct myself. It seems it has nothing to do with the value of x, since NNBEG is not a valid name, but NN4BEG would be. The letters N, E, S, W are therefore an addition, not a replacement. The addition is also sometimes made to JUMP wires, so JN, JE, JS, JW, exist, but JJ does not exists.

Sorry for the confusion! My main question from the title still remains.

KelvinChung2000 commented 11 months ago

I have no deep knowledge of the FABulous architecture. I recalled that the NN, EE, indicates a double wire. You will not have things like JN or JE because the jump wire is internal to the tile. @gatecat will be able to give a better answer.

IAmMarcelJung commented 11 months ago

Thanks for your reply! I also thought that JN or JE don't exist, but they exist in fabric.csv and also appear in the .fasm file. That's one part that confused me.

KelvinChung2000 commented 11 months ago

Maybe look into the .list file. That might be useful.

IAmMarcelJung commented 8 months ago

I just talked to @dirk-koch and he cleared things up. The naming is historically grown (as @everythingelsewasalreadytaken also had previously guessed in a private talk). One naming scheme was used when only smaller fabrics were built. The other naming scheme came on top when bigger fabrics had to be built and more routing needed to be added. To distinguish between "old" and "new" routing resources, a different naming scheme was used rather than using the same one. So in short, those wires with two letters do not differ in functionality from those with one letter.