Custom IC SKILL - Recent Threads

RE: Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Wed, 14 Oct 2026 03:18:27 GMT

I’ve only touched PDK (Skill/PCell) for half a year and haven’t systematically learned process knowledge and Skill coding. So I’m using these PCell codes as my entry point for structured study. Despite some bugs, they let me understand the general framework. Haha, I still need to learn much more about process and Skill.

Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Tue, 29 Sep 2026 04:16:30 GMT

Hi,

Cadence provided us with the Skill code for the MOS PCell. I've been learning it and ran into some issues, so I'd appreciate your help. Thanks.

Known information (from Cadence official):

;;substrateContact? specifies whether contacts are necessary or not on the
;; source and drain of the transistor, and then creates it.

;;leftContact? the left side of the transistor be it the source or
;; drain

;;rightContact? the right side of the transistor be it the source or
;; drain

;;transistor_length length of the transistor's active area
;; (note: this is a distance measured in the X-direction).
;; (float, default = 1.0)

;; car(substrateRules) = tap diffusion layer.
;; cadr(substrateRules) = tap diffusion contact enclosure.
;; caddr(substrateRules) = tap diffusion to active spacing.
;; cadddr(substrateRules) = tap diffusion to gate poly spacing.
;; car(cddddr(substrateRules)) = tap implant rules.

;;contactWidth the width of the contact layer being used for
;; connections
;; (default = 1.0)

(leftStretch techGetSpacingRule(techGetCurrentTechFile() "minSpacing"
techParam("poly") techParam("cont")) + techGetSpacingRule(
techGetCurrentTechFile() "minWidth" techParam("cont")) +
techGetOrderedSpacingRule(techGetCurrentTechFile() "minEnclosure"
techParam("ndiff") techParam("cont")) )

(rightStretch techGetSpacingRule(techGetCurrentTechFile() "minSpacing"
techParam("poly") techParam("cont")) + techGetSpacingRule(
techGetCurrentTechFile() "minWidth" techParam("cont")) +
techGetOrderedSpacingRule(techGetCurrentTechFile() "minEnclosure"
techParam("ndiff") techParam("cont")) )

Code segment with questions (from Cadence official):

;;*************************************************************************
;;
;;The following adjusts the rightStretch to account for the substrateContact
;;---------------------------------------------------------------------
;;
;;*************************************************************************
when( substrateContact? && substrateContact? !="FALSE"
if( leftContact? && leftContact? != "FALSE" &&
rightContact? && rightContact? != "FALSE" then
else
xtrWidth = leftStretch + transistor_length + rightStretch
minSubTie = contactWidth + 2 * cadr(substrateRules)
; fprintf( stdout "xtrWidth minSubTie %L\n" list(xtrWidth minSubTie) )
when( xtrWidth < minSubTie
rightStretch = rightStretch + minSubTie - xtrWidth
)
)
)

My Questions:

1.The source code uses an if-then-else structure. I believe the correct form should be either if-then or if-else.

2.What is the purpose of this piece of code? Why does it only adjust rightStretch, with no case to adjust leftStretch?

3.I am particularly confused by this line of code:

when( xtrWidth < minSubTie
rightStretch = rightStretch + minSubTie - xtrWidth
)

Why do we need to consider the scenario where xtrWidth is smaller than minSubTie? And why is rightStretch calculated as rightStretch + minSubTie - xtrWidth under this condition?

I would appreciate your insights. Thank you.
Steve

RE: Question on Skill Code for Cadence Official MOS PCell

Andrew Beckett — Sun, 11 Oct 2026 21:18:59 GMT

Yes, that's correct. You'd have seen that if you'd tried it (which is what I did). It's clearly an assumption in the code (trying to cater for every possible scenario is hard, and in most technologies I've seen the gate extension is larger than the poly to diffusion spacing so it probably didn't get caught in testing when this sample was created almost 30 years ago. It is a sample after all - not guaranteed to be perfect.

RE: Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Thu, 08 Oct 2026 03:19:30 GMT

Hi Andrew,

I came across a new problem when going over the code and hope to get your input.

Code segment with questions (from Cadence official):
;; Route poly if needed
when(routePoly && routePoly != "FALSE" && numberOfFingers > 1
strap_width = ((numberOfFingers - 1) * gatePitch) +
transistor_length
strap_offset = gate_Extension - diffusionGateSpace
polyfig = rodCreatePath(
?cvId cellViewId
?layer gateLayer
?width minPolyWidth
?pts list(0:0 strap_width:0)
?termName "G"
?pin t
?termIOType "input"
)
cond(
( routePolydir == "Top"
rodAlign(
?alignObj polyfig
?alignHandle "lowerRight"
?refObj topPin
?refHandle "upperRight"
?ySep -strap_offset
)
)
( routePolydir == "Bottom"
rodAlign(
?alignObj polyfig
?alignHandle "upperRight"
?refObj botPin
?refHandle "lowerRight"
?ySep strap_offset
)
)
)
polyfig~>dbId~>pin~>name = "gatePin"
spcClearGatePins( gatePins )
)

My Questions:

My question: I understand that strap_offset is used to meet DRC requirements. However, if the value of diffusionGateSpace is larger than gate_Extension, wouldn’t that mean polyfig is not placed right next to topPin / botPin? They would be separated by a distance of |strap_offset|. The intended behavior is that all gates (in the multi-finger case) are connected together by polyfig. This is where I’m confused.

Best regards,
Steve

RE: Placing a dock window to left of layout screen, above the Layer Palette

blankman — Wed, 30 Sep 2026 09:36:45 GMT

Hi Andrew, that is myself, my apologies, I had forgotten about this past log. Will update latest case. Kind regards

Placing a dock window to left of layout screen, above the Layer Palette

blankman — Mon, 28 Sep 2026 14:33:54 GMT

Hi,

I am trying to dock a window to the left of my layout window, and above the existing Layer Palette. However no matter what value I place for "?index" (see below), it always places the dock window on the left side, but BELOW the Layer Palette, ie bottom left of layout window. Is it possible to dock the window to the TOP left of the layout window?

Thanks

hiDockWindow

hiDockWindow(
?window w_dwindowID
[ ?session g_sessionWindowID ]
[ ?side s_side ]
[ ?index x_index ]
[ ?unmapped g_unmapped ]
[ ?tabOnto w_dwindowID ]
)

RE: Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Wed, 30 Sep 2026 01:36:30 GMT

Hi Andrew,

Thank you so much for taking the time to look into this and give such a detailed explanation!

Now I understand the big picture: this sample has a complete framework to add device definitions into the tech library. I also get why the code only adjusts rightStretch for substrate tie abutment. That makes sense now.

I will check out the PCell Designer video you shared.

Thanks again for your patient help!

Best regards,
Steve

RE: Placing a dock window to left of layout screen, above the Layer Palette

Andrew Beckett — Tue, 29 Sep 2026 18:45:11 GMT

I see you logged a support case about this (47030722) - at least I assume it's you because the wording is identical. You also logged a support case in November 2023 on the same topic (46745168) for which CCR #2906238 was filed. That hasn't been resolved yet (note, I didn't test it myself - as there's an AE already working on this I like to avoid double working).

Andrew

RE: Question on Skill Code for Cadence Official MOS PCell

Andrew Beckett — Tue, 29 Sep 2026 18:12:29 GMT

OK, I took a look.

The code is fairly complicated - it contains a whole load of infrastructure to install and configure various devices by adding extra information into your tech file and then installing the devices in the tech library too.

To set up, you'd use:

setSkillPath(cons(prependInstallPath("samples/ROD/rodPcells") getSkillPath()))
load("install/spcLoadInstall.il")

and then interact with the UI. You have to select the devices you want, choose the appropriate layers to use, and then fill in any missing design rule info that can't already be found in the tech file (sometimes these might be because of table rules).

The code is not being maintained and it's just a sample - whether you'd want to start from this or not is another matter. I'd probably recommend using PCell Designer instead if you can get access to it - see this video: Creating a Simple MOSFET with PCell Designer

To answer your questions:

It's a little unusual, but having an empty then within an if/then/else is OK. It potentially makes it simpler to edit in the then part if you decide you need it later.
The rightStretch and leftStretch parameters are hidden parameters which are then altered by the abutment function when two transistors are abutted. If you've chosen to have the substrate contact enabled at the top/bottom, it may have to adjust the size of the diffusion to allow for these substrate contacts, but it only really needs to do it on one side - and in this case the right side is used.
This is (I think) trying to handle the scenario where the substrate contact protrudes beyond the transistor width (in this case it's the overall width of the device, not the width of the gate). That's where you'd have a problem with the substrate contacts hitting each other otherwise, so more space needs to be allowed.

Hope that helps!

Regards,

Andrew

RE: Question on Skill Code for Cadence Official MOS PCell

Andrew Beckett — Tue, 29 Sep 2026 14:10:11 GMT

Steve,

Thanks for the reference. I've not looked at those samples for many years (I think they were written almost 30 years ago).

I'll take a look during today and then can hopefully answer your questions having inspected the full code.

Regards,

Andrew

RE: Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Tue, 29 Sep 2026 13:38:44 GMT

Hi Andrew,

Thanks a lot for your advice. I don’t know who wrote these sample code files, but I suspect they are located under a path like /eda/cadence/IC618/tools/dfII/samples/ROD/rodPcells/components/mos.

I find MOS PCells really interesting, yet quite challenging for me. If you happen to have time, feel free to check if this example is available under that path. I would really appreciate it.

Best regards,

Steve

RE: Question on Skill Code for Cadence Official MOS PCell

SZ20260803361 — Tue, 29 Sep 2026 11:10:33 GMT

Hi Andrew,

Thank you very much for your detailed reply. I mistakenly assumed this was provided by Cadence official. I will refer to it as a "MOS PCell sample code" going forward.

Unfortunately, I do not know who authored this code, so I am unable to contact the original developer. I will loaded the full code to the thread.(Cadence won’t let me upload .tar or .zip files, so I have to paste the code directly into the post. Sorry it looks messy)

I am eager to learn how to write PCells for MOS, BJT and other devices using Skill. As you mentioned, technologies are often different. My plan is to learn fundamental PCell implementation from this example first. With continued practice, I hope to eventually build PCells that adapt to different foundry processes.

However, teaching resources for PCell development are quite limited from what I can find. That is why I am seeking guidance from you and other experts. I hope my questions will not disrupt your work or take up too much of your time.

Thank you for your contributions to the Cadence Community and for helping me with my questions.

Best regards,

Steve

RE: Writing lists to file

Aurel B — Tue, 29 Sep 2026 09:26:25 GMT

The following functions might be a bit simpler to use:

writeTable and readTable

In more recent versions, there is also:

jsonSave and jsonReadFile

Writing lists to file

blankman — Mon, 28 Sep 2026 21:16:27 GMT

Hi,

I have a question in relation to storing captured data to file for recall.

Brief background: I have 2 procedures, one stores the list of layers in the Layer Palette that are visible, and the other recalls those layers and sets them visible, ie for storing of custom layer visibility sets. (aware that this feature already exists within Virtuoso, coding as part of a larger project)

Question I have: when the layers set is stored, and then Virtuoso is closed and reopened, the layers set is lost. What I want to do is store the layers list to file, so that any stored list is permanently stored irrespective of whether the tool is closed.

I also want to be able to store 5 different lists of layers, ie for storing of 5 different custom layer visibility sets at a time.

Having not approached a task like this before in skill, I am wondering if there is any examples of this I could reference, or any advice how to go about accomplishing this?

Thanks very much in advance

RE: Writing lists to file

Andrew Beckett — Tue, 29 Sep 2026 05:34:04 GMT

I'd suggest just writing out some kind of list structure into the file using pprint(theList filePort) or even just fprintf(filePort "%L\n" theList).

You can then read it back in using lineread or read - these will use the SKILL parser to read in the list structure even if spread over multiple lines.

Andrew

RE: Question on Skill Code for Cadence Official MOS PCell

Andrew Beckett — Tue, 29 Sep 2026 05:31:22 GMT

As far as I'm aware there's no such thing as a "Cadence Official MOS PCell". I can only assume this is some sample that's been provided (I don't recognise the code and a bit of searching hasn't allowed me to locate it). The reason why there would be no "Official MOS PCell" is that technologies are often different so having a one-size-fits-all would be unlikely...

I suggest you ask your questions to whomever from Cadence provided you with the sample code.

There's no problem with having if(condition then then_code else else_code) even if the then_code is empty (it's a bit odd having the then keyword if you don't have any associated code - I'd probably just have used unless instead). For the rest of the questions I couldn't answer without seeing the rest of the code (and even then I'd need to know the intent - hence my suggestion for you to contact the person who provided you with the example).

Regards,

Andrew

RE: Placing a dock window to left of layout screen, above the Layer Palette

blankman — Mon, 28 Sep 2026 16:15:52 GMT

Thanks Steve, appreciate the response, though hoping to do this by default upon calling hiDockWindow, ie without having to drag and drop. Know if this is possible? Thanks again

RE: How to get ADE outputs priority

kkdesbois — Mon, 28 Sep 2026 15:28:35 GMT

Thanks for the confirmation. Case created.

How to get ADE outputs priority

kkdesbois — Wed, 16 Sep 2026 07:05:08 GMT

Hello,
Is there any way to get the priority of ADE outputs?

The weight can be accessed with the function axlgetSpecWeight but I can not find an equivalent function for priority.

Laurent.

RE: Placing a dock window to left of layout screen, above the Layer Palette

SZ20260803361 — Mon, 28 Sep 2026 15:05:50 GMT

Hello,

There is a simple way to achieve this, you can drag the dockwindow to the top of the Palette.

Thanks,
Steve

RE: How to get ADE outputs priority

Andrew Beckett — Fri, 25 Sep 2026 16:16:26 GMT

Hi Laurent,

Apologies - I didn't see this post (I think there may have been a problem with notifications for a while - I should go back and look for anything I missed).

As far as I can see there is no public function for this. Even the maeSetSpec doesn't have the option to set it - but we probably ought to have an maeGetSpec function to retrieve this kind of information. Please contact customer support and request this as an enhancement.

Kind Regards,

Andrew

RE: How to get ADE outputs priority

kkdesbois — Fri, 25 Sep 2026 15:48:34 GMT

I guess it is not possible.

RE: How to get the top level coordinate of an instance on lower level?

Martinsh — Tue, 22 Sep 2026 02:08:45 GMT

Hi, Andraw,

It's clear now. Thanks a lot!

BR,

Martinsh

How to get the top level coordinate of an instance on lower level?

Martinsh — Thu, 10 Sep 2026 03:12:00 GMT

There is a cell named CellX in a hierarchical layout design. The cell CellX is placed on one of lower level of the layout design. How to get the top level coordinate of the bBox of the cell CellX?

Thanks!

RE: How to get the top level coordinate of an instance on lower level?

Andrew Beckett — Mon, 21 Sep 2026 17:43:37 GMT

Actually, it's not doing that. You're getting the transformation of the final instance, rather than to a shape within that final instance.

If there had been more levels of hierarchy, you'd see it's the concatenated transformations excluding the final instance. One way of seeing this would be if you did:

dbCreateRect(cv "Metal4" dbTransformBBox(car(last(inst))~>bBox dbGetHierPathTransform(inst)))

This would draw the rectangle exactly covering the final leaf instance. That's because the bBox is already the bBox of the final rotated/mirrored/translated instance, so it doesn't need the final transformation applied.

Or you could do:

dbCopyFig(car(last(inst)) cv dbGetHierPathTransform(inst))

which would take the leaf instance (with it's transformation) and then copy that to the top-level.

To illustrate what I mean, if you went down inside the final instance and used something inside that, you'd need to include the final leaf's transformation - which is what dbGetInstTransform does:

dbCreateRect(cv "Metal5" dbTransformBBox(car(last(inst))~>master~>bBox dbGetInstTransform(inst)))

Because the bBox is taken here from the master, it's in the coordinate system of the final cellView itself rather than the parent instance - so needs the extra level of transformation to be taken into account.

Hope that helps (and my explanation was not too confusing).

Regards,

Andrew