Magic quick reference¶

Official tutorials: http://opencircuitdesign.com/magic/tutorials/

Launch¶

. /foss/designs/common/.designinit
cd /foss/designs/lab2_layout
echo "source \$PDK_ROOT/sky130A/libs.tech/magic/sky130A.magicrc" > .magicrc
magic -d X11 -T sky130A mycell.mag &

Use the X11 driver. The OpenGL and Cairo drivers can fail with a pixmap allocation error inside the container.

Magic opens two windows: the layout window, and tkcon, a Tcl console where you type commands. Anything below written as a command goes in tkcon.

The box¶

Magic has no free-floating cursor selection. Almost every operation acts on the box, a rectangle you position first.

Action	How
Place the box	left-click one corner, right-click the other
Set it exactly	`box <llx> <lly> <urx> <ury>`
Read it back	`box values`
Use microns	`box 0um 0um 2um 1um`

Painting¶

Action	How
Paint a layer into the box	middle-click the layer, or `paint <layer>`
Erase a layer from the box	`erase <layer>`
Erase everything in the box	`erase`
Undo / redo	`u` / `Shift-U`

Common SKY130 layers: ndiffusion, pdiffusion, poly, nwell, ndcontact, pdcontact, polycontact, m1, m2, via1.

Magic infers devices from overlap. Paint poly across ndiffusion and the overlap becomes an nmos; you never place a transistor as an object.

View¶

Action	Key / command
Zoom to fit	`v`
Zoom in / out	`z` / `Shift-Z`
Pan	arrow keys
Expand subcells	`x` (`Shift-X` to collapse)
Show what is under the box	`what`

An unexpanded subcell draws as an empty rectangle with its name. If a layout looks blank, expand it.

Selecting and moving¶

Action	How
Select what is under the box	`s`
Select an entire cell	`S`
Select a whole connected net	`select net`
Move the selection	`m` plus a direction, or arrow keys
Copy	`c`
Delete	`d`

Labels¶

label VDD          # label the box on the current layer
label GND!         # a trailing ! makes the name global

Label every port. LVS matches by name: an unlabelled or misspelled port is the usual reason Netgen reports a mismatch on an otherwise correct layout.

DRC¶

DRC runs continuously. White dots mark violations, and the toolbar shows a live count.

Command	Meaning
`drc check`	re-run over the whole cell
`drc count`	how many violations
`drc why`	explain the violations under the box
`drc catchup`	finish any pending background checking

Target zero before extracting. drc why names the rule, which is faster than guessing at spacing.

Extraction, LVS, PEX¶

extract all                 # build the .ext files
ext2spice lvs               # device-level netlist, no parasitics
ext2spice -o cell.lvs.spice

extract all                 # for PEX, extract again
ext2spice cthresh 0         # keep every coupling capacitance
ext2spice -o cell.pex.spice

cthresh 0 is what makes the difference between the pre- and post-PEX netlists: without it, capacitances below the threshold are discarded.

Compare against a schematic with Netgen:

# Prefer the course wrapper -- it handles the netgen quirk below for you:
/foss/designs/scripts/run_lvs.sh cell.lvs.spice xschem/cell_lvs.sch

# Raw netgen, if you want it. Strip XSchem's commented top-level block first:
awk '/^[*][*][.]subckt/{s=1;next} /^[*][*][.]ends/{s=0;next} !s' \
    cell_sch.spice > cell_sch.netgen.spice
netgen -batch lvs "cell.lvs.spice cell" "cell_sch.netgen.spice cell" \
       $PDK_ROOT/sky130A/libs.tech/netgen/sky130A_setup.tcl

A clean run reports Circuits match uniquely.

Batch use¶

magic -dnull -noconsole -T sky130A <<'EOF'
load mycell
drc check
puts "errors: [drc list count total]"
quit -noprompt
EOF

Magic reads commands on stdin in GUI mode too, which is the reliable way to script it:

( echo "view"; echo "drc check"; sleep 200 ) | magic -d X11 -T sky130A mycell.mag &

Devices from the PDK¶

magic::gencell sky130::sky130_fd_pr__nfet_01v8 myfet w 1 l 0.5

This drops a parameterised device as a subcell, so it appears as a named rectangle until you expand it with x. For Lab 0 and Lab 2 you paint the layers yourself instead.

Common failures¶

Symptom	Cause
Layout looks empty, one named rectangle	An unexpanded subcell. Press `x`.
`Failed to load technology`	No `.magicrc` in the working directory.
Netgen reports a mismatch on correct-looking layout	Missing or misspelled port labels.
Nothing happens when you paint	The box is empty or off-screen. `box values` to check.