Modification of efabless' chip_io padframe with a library of pre-configured IO cells instead of the caravel harness.

A select number of cells is presented here under the gds/io_cells folder. These include the following cells:

• sky130_ef_io__gpiov2_pad_wrapped: This is the modified version of the same cell from caravel. In this version of the cell, all the configuration pins not related to configuring IO cell direction are pre-tied accordingly to create a Digital I/O with Strong/Strong drive. This configuration disables the analog input capability of the IO cell as we have opted instead to use the dedicated analog IO cells for this purpose.
• sky130_ef_io__gpiov2_pad_wrapped_input/output: These are further modified versions of the GPIO cell pre-configured for input or output, with all relevant config pins pre-tied and only the IO cell chip-side input/output pin exposed. These can be placed interchangeably with the existing IO cells in the event a runtime-configurable IO cell is not necessary.
• sky130_ef_io__analog_pad: This is the analog pad used in the IO ring, which is just a short. This is the same analog pad used in the chip_io_alt padring provided in caravel with no modifications. The wrapped version of this cell contains additional ring slices to match the width of the GPIOv2 cell.

The padframes are located in gds/padframes and include the following cells:

• chip_io: This is a direct copy of the chip_io padring from the caravel project. The GPIO cells however are referencing the modified sky130_ef_io__gpiov2_pad_wrapped cell included here.
• chip_io_propel: This is a modified version of chip_io for the PROPEL project, including several analog pads used in the chip_io_alt padring from caravel.
• chip_io_empty: This is a version of chip_io where all the GPIO cells have been removed (the met5 pad shapes remain). This is intended to be used as a template where the user can fill in the spaces with the IO cells they intend to use.
• chip_io_sealed: This is a version of chip_io instanced within a seal ring.
• advSeal_6um_gen: This is the seal ring provided as part of caravel. This is the same file as found in caravel/gds.