Using lots of new devices today! I have generated a MiM cap using Metal3/Metal 4. Assuming the capacitor is the giant square on the left? Do I simply wire m3/m4 strips directly to this, for either side of the capacitor? Also, what is the vertical stripe of M3/M4 on the right for?

Yes, the capacitor is the large square to the left. The stripe on the right is a contact to the bottom plate. The "best practice" for avoiding antenna discharge problems during manufacture is to contact upwards from the bottom plate. So the two connections should be a M4 wire directly to the capacitor contact on top, and a M4 wire to the contact on the right.

I have been trying to avoid using Metal 4 for anything in the design, so as not to disturb Caravel's PDN. Will the M4 capacitor wires cause any issue - do I need a keep-out area?

I think you can use

m4

in a macro. The LEF you write has the block-out shape. You just need to make sure after placement that a proper powergrid is done by OL, and nothing shorts. There are frequently tool bugs so that the PDN is not properly created.

Oh that is interesting that the LEF has the block-out shape. I was actually using

m4

in my Macros to draw vertical power lines, and labelling them with

vccd1

etc, so that Caravel's PDN would pick them up and power my macro. This was on the advice of some other users. Is this your approach too, or do you think these

m4

strips are getting blocked-out when generating the LEF? I was getting some problems with my macro powering up after routing through OL, so maybe that is a contributing factor! I never did get to the bottom of it.

I have not tried to stuff analog macros into an openlane flow myself, but the SRAM block is commonly used in that context, and it has its own power connections, and it's possible to get openlane to route the power nets and make the right connections. So I know it can be done.

I had to use MIMCAPs in macros, as far as I know the PDN-generator reads the

.lef

file and then avoids all

OBS

structures, and specific

PIN

layers (in the same layer + their nets are explicitely specified in OpenLane configuration

FP_PDN_MACRO_HOOKS

). Other PIN layers are being ignored (causing shorts). m4 power rails: Should be connected via m5 if they are specified in

FP_PDN_MACRO_HOOKS

and m5 can reach them Mimcaps: worked for me with the power nets. But with different nets, adding obstructions might be necessary

Really useful thank you!

@Ellen Wood Sometimes it is easier to edit the

.mag

file directly in a texteditor, than to draw in magic using the GUI. Just a hint, in case you were not aware. Also a LEF/DEF is just ASCII, you can manipulate directly if useful.

@Harald Pretl do you mean for creating

OBS

areas etc? I haven't tried that yet but sounds like a good idea!

Exactly. Sometimes modifying OBS is just easier this way. Also adding pins in magic I do with

vim

, quicker than in magic. I just put a label in magic via the GUI, the rest I do with vim 🙂

That is great to know 😊 (assuming PINs are the same as PORTs?)

Yes, sorry 😀