********************************* Hello <!channel> GFMPW-1 is now open for project submissions. This shuttle is a follow-on for the GF180 shuttle program and is sponsored by Google. The deadline for project submissions for GFMPW-1 is December 11, 2023 @ 11:59pm PST. Please use the

gfmpw-1a

tag for caravel_user_project for creating and updating your projects. See the following shuttle page for further information ( https://efabless.com/gf-180-open-mpw-shuttle-program ). I would encourage you to get your projects submitted early as submission time will be a factor in selection for GFMPW-1. *********************************

No support to analog design?

@jeffdi @Tim Edwards the website says

This shuttle will support digital designs using the OpenLane design flow. There is not a supported open source flow for analog design.

Can we still attempt to go with a digital flow and place some analog / black box’d macros for something mixed signal?

@Abhinav Uppal: I'm not exactly sure how/if that will work for the tapeout process. Technically, there is nothing wrong with doing analog other than the fact that we do not have combination analog/digital GPIO cells like we do on Sky130. So there is no way to get an analog signal on or off chip.

I understand, thank you. Is there a plan to add analog I/O or allow us to modify the padframe for this or perhaps a future shuttle? We are just trying to figure out if it would make sense for us to port our mixed signal design from sky130 to GF180 now or not…

Yes, the intention is to allow people to be able to run analog on GF180 in the future. Either I will adapt a pad to add analog capability or else create some kind of method like that which is currently used for setting GPIO power-on defaults, but used to select which type of pad to use. The latter can get very complicated because the pinout to the user project changes any time a pad type changes. Maybe a "caravan" version for GF180 is justified, but that would limit analog I/O to just the 11 analog pads unless I also make the change to allow analog connections to the GPIO.

Ah I see configurable GPIO could get involved. But for the current Dec11 shuttle, if we only needed say two analog inputs for a test structure, would it make sense to use any of the user area supplies as analog inputs? Or are there dcaps or something on the pad frame that would make this impossible?

Unfortunately, the GF padframe does not have buses that can be isolated, so currently all VDD pads are tied together internally and all VSS pads are tied together internally. That said, I just looked at the layout of the GPIO pad and determined that it is possible to bring out the pad connection to the core (through an ESD resistor) in a manner similar to sky130, with very little effort, and I'm going to propose that to the team and see if we can push it through. Unfortunately, that changes the user project wrapper pinout and so requires updates to essentially everything, including the digital flow, the tapeout process, precheck, and all repositories, so I expect it is unlikely that I can get that done for this tapeout.

I understand, thank you for checking! If the ESD resistor is something that could be integrated into a blackbox’d analog macro, perhaps we could still bring some analog in as long as the pad could be configured though the RISC to perhaps not digitally buffer the input. Will look forward to hearing more about this, thank you so much Tim!

@Abhinav Uppal: If I can't get the change approved, there is a possibility that you could implement the additional routing directly into your user project wrapper. That would fail precheck, of course, because you would be routing outside the user project wrapper. But we can manually override precheck, so I think it would work (an early submission to test it would be advisable). Here is the proposed layout change:

Branch gfmpw-1a has problem. Makefile has a problem. Pdk-with-vokare target has a problem. PDK=gf180mcuC has a problem. Creating a git repo from https://GitHub.com/efabless/caravel_user_project/generate has a problem. Please look into them. Could install NEITHER gf180mcuC NOR gf180mcuD.

@Lab Lecture: We are aware that it went badly wrong and are in the process of fixing it.