Excited to start testing! Request to Efabless. Please extend the Caravel datasheet tables to include more than just the Maximum Ratings (https://caravel-harness.readthedocs.io/en/latest/maximum-ratings.html). There should be sections for both Recommended Operating Conditions and Electrical Characteristics. Two versions are needed, one for SkyWater and another for Global Foundries. The following should be covered: • Which I/O primitives were implemented? • Are the inputs LVCMOS/TTL or CMOS threshold levels (+1.4V or 70%*VDD)? • Are the inputs Schmitt trigger, bus keeper or simple buffers? • What is the slowest allowable input slew rate (to avoid oscillation)? • Output drive characteristics The GF180 PDK is specified at both +3.3V and +5V. Are there any constraints for running the GF Caravel MPW0 at either I/O voltage? If the answers have already been posted, please indicate link. Thank you. :)

@Wallie Everest: The I/O pad used for the user GPIO pins is the SkyWater GPIOv2, and the documentation for it (and the other I/O pads) is here: https://skywater-pdk.readthedocs.io/en/main/contents/libraries/sky130_fd_io/docs/user_guide.html. Most of your questions have answers in that documentation somewhere, but the short answers are: (1) The GPIOv2 was used for basic I/O. There is only one other non-power pad used, which is the xres4v2 for the RESETB input. (2) Inputs are selectable for TTL or CMOS operation; see the GPIOv2 description for details. (3) There is a bus keeper function that is not really usable without low-power mode support over the entire chip. This is something that we plan to work on for some future caravel version. Otherwise the GPIOs are simple buffers. The xres4v2 is not a schmitt trigger, but does have a deglitching filter. (4) I'm unsure about the slew rate limit and I don't think any value is documented in the SkyWater documentation. (5) Output drive characteristics can be found in the documentation. The GF version uses the GF "bi_t" pad; it differs from the SkyWater pad in that it does not have selectable CMOS/TTL modes but does have selectable drive strength and slew rate. The GF I/O pads are designed to run at 5V nominally. They are characterized at 3.3V but are much slower. Ping me again tomorrow and I'll track down the links to more documentation.

Thank you so much for the prompt and thorough answer. I will share with others.