Different tile coordinate system in Documenation and bel files

FPGA-Research-Manchester / FABulous

Fabric generator and CAD tools

https://fabulous.readthedocs.io/en/latest/

Apache License 2.0

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Different tile coordinate system in Documenation and bel files #143

Closed IAmMarcelJung closed 10 months ago

IAmMarcelJung commented 10 months ago

In the Documentation, the tile coordinate system has its origin in the top left corner:

However, in the bel files (both bel.txt and belv2.txt), the first line states that it is in the bottom left corner: # BEL descriptions: bottom left corner Tile_X0Y0, top right Tile_X10Y16

Which one is the correct layout? Or am I getting something wrong? Thanks in advance for any kind of help!

TaoBi22 commented 10 months ago

Hi @IAmMarcelJung,

IIRC, this was because of a discrepancy between the coordinate systems used internally within FABulous and within nextpnr - you can see a relic of having to convert between the two systems here. I just had a look, and it looks like these days both bel representations also start at the top-left corner, so this comment is now out-of-date. Thanks for catching that, I'll get it fixed!

IAmMarcelJung commented 10 months ago

Nice thanks! This really got me confused for a moment, although I was quite sure it is correct in the documentation :)