Magic Tutorial #1: Getting Started
Magic Tutorial #1: Getting Started
Magic Tutorial #2: Basic Painting and Selection
Commands introduced in this tutorial:
:array, :corner, :fill, :flush, :plow, :straighten, :tool, :wire
Macros introduced in this tutorial:
2.; it allows you to place wires by pointing at the ends of legs rather than by positioning the box, and also provides for convenient contact placement. Plowing is the subject of Section3. It allows you to re-arrange pieces of your circuit without having to worry about design-rule violations being created: plowing automatically moves things out of the way to avoid trouble.
This command prints out the name of the current tool and the meaning of the buttons. Run Magic on the cell tut3a and type :tool info.
The :tool command can also be used to switch tools. Try this out by typing the command
Magic will print out a message telling you that you're using the wiring tool, and the cursor will change to an arrow shape. Use the :tool info command to see what the buttons mean now. You'll be using the wiring tool for most of the rest of this section. The macro `` '' (space) corresponds to :tool. Try typing the space key a few times: Magic will cycle circularly through all of the available tools. There are three tools in Magic right now: the box tool, which you already know about, the wiring tool, which you'll learn about in this tutorial, and the netlist tool, which has a square cursor shape and is used for netlist editing. ``Tutorial #7: Netlists and Routing'' will show you how to use the netlist tool.
The current tool affects only the meanings of the mouse buttons. It does not change the meanings of the long commands or macros. This means, for example, that you can still use all the selection commands while the wiring tool is active. Switch tools to the wiring tool, point at some paint in tut3a, and type the s macro. A chunk gets selected just as it does with the box tool.
Once you've selected the wiring material, the right button paints legs of a wire. Left-click on label 1 to select the red material, then move the cursor over label 2 and right-click. This will paint a red wire between 1 and 2. The new wire leg is selected so that you can modify it with selection commands, and the box is placed over the tip of the leg to show you the starting point for the next wire leg. Add more legs to the wire by right-clicking at 3 and then 4. Use the mouse buttons to paint another wire in blue from 5 to 6 to 7.
Each leg of a wire must be either horizontal or vertical. If you move the cursor diagonally, Magic will still paint a horizontal or vertical line (whichever results in the longest new wire leg). To see how this works, left-click on 8 in tut3a, then right-click on 9. You'll get a horizontal leg. Now undo the new leg and right-click on 10. This time you'll get a vertical leg. You can force Magic to paint the next leg in a particular direction with the commands
Try out this feature by left-clicking on 8 in tut3a, moving the cursor over 10, and typing :wire ho (abbreviations work for :wire command options just as they do elsewhere in Magic). This command will generate a short horizontal leg instead of a longer vertical one.
Once you've drawn the purple leg to 4, move the cursor over red material and middle-click. This time, Magic prints an error message and treats the click just like a left-click. Magic only knows how to make contacts between certain combinations of layers, which are specified in the technology file (see ``Magic Maintainer's Manual #2: The Technology File''). For this technology, Magic doesn't know how to make contacts directly between purple and red.
When you first start wiring, you may not be able to find the right kind of material anywhere on the screen. When this happens, you can select the wiring material and width with the command
Then move the box where you'd like the wire to start, switch to the wiring tool, and right-click to add legs.
It's often hard to position the cursor so that a wire leg comes out right the first time, but it's usually easy to tell whether the leg is right once it's painted. If it's wrong, then you can use the stretching commands to shift it over one unit at a time until it's correct.
fill direction [layers] corner direction1 direction2 [layers]
To see how they work, load the cell tut3b. The :fill comand extends a whole bunch of paint in a given direction. It finds all paint touching one side of the box and extends that paint to the opposite side of the box. For example, :fill left will look underneath the right edge of the box for paint, and will extend that paint to the left side of the box. The effect is just as if all the colors visible underneath that edge of the box constituted a paint brush; Magic sweeps the brush across the box in the given direction. Place the box over the label ``Fill here'' in tut3b and type :fill left.
The :corner command is similar to :fill except that it generates L-shaped wires that follow two sides of the box, travelling first in direction1 and then in direction2. Place the box over the label ``Corner here'' in tut3b and type :corner right up.
In both :fill and :corner, if layers isn't specified then all layers are filled. If layers is given then only those layers are painted. Experiment on tut3b with the :fill and :corner commands.
When you're painting bundles of wires, it would be nice if there were a convenient way to place contacts across the whole bundle in order to switch to a different layer. There's no single command to do this, but you can place one contact by hand and then use the :array command to replicate a single contact across the whole bundle. Load the cell tut3c. This contains a bundle of wires with a single contact already painted by hand on the bottom wire. Type s with the cursor over the contact, and type S with the cursor over the stub of purple wiring material next to it. Now place the box over the label ``Array'' and type the command :array 1 10. This will copy the selected contact across the whole bundle.
The syntax of the :array command is
This command makes the selection into an array of identical elements. Xsize specifies how many total instances there should be in the x-direction when the command is finished and ysize specifies how many total instances there should be in the y-direction. In the tut3c example, xsize was one, so no additional copies were created in that direction; ysize was 10, so 9 additional copies were created. The box is used to determine how far apart the elements should be: the width of the box determines the x-spacing and the height determines the y-spacing. The new material always appears above and to the right of the original copy.
In tut3c, use :corner to extend the purple wires and turn them up. Then paint a contact back to blue on the leftmost wire, add a stub of blue paint above it, and use :array to copy them across the top of the bundle. Finally, use :fill again to extend the blue bundle farther up.
where direction is a Manhattan direction like left and layers is an optional, comma-separated list of mask layers. The plow command treats one side of the box as if it were a plow, and shoves the plow over to the other side of the box. For example, :plow up treats the bottom side of the box as a plow, and moves the plow to the top of the box.
As the plow moves, every edge in its path is pushed ahead of it (if layers is specified, then only edges on those layers are moved). Each edge that is pushed by the plow pushes other edges ahead of it in a way that preserves design rules, connectivity, and transistor and contact sizes. This means that material ahead of the plow gets compacted down to the minimum spacing permitted by the design rules, and material that crossed the plow's original position gets stretched behind the plow.
You can compact a cell by placing a large plow off to one side of the cell and plowing across the whole cell. You can open up space in the middle of a cell by dragging a small plow across the area where you want more space.
To try out plowing, edit the cell tut3d, place the box over the rectangle that's labelled ``Plow here'', and try plowing in various directions. Also, try plowing only certain layers. For example, with the box over the ``Plow here'' label, try
Nothing happens. This is because there are no metal2 edges in the path of the plow. If instead you had typed
only the metal would have been plowed to the right.
In addition to plowing with the box, you can plow the selection. The command to do this has the following syntax:
:plow selection [direction [distance]]
This is very similar to the :stretch command: it picks up the selection and the box and moves both so that the lower-left corner of the box is at the cursor location. Unlike the :stretch command, though, :plow selection insures that design rule correctness and connectivity are preserved.
Load the cell tut3e and use a to select the area underneath the label that says ``select me''. Then point with the cursor to the point labelled ``point here'' and type :plow selection. Practice selecting things and plowing them. Like the :stretch command, there is also a longer form of :plow selection. For example, :plow selection down 5 will plow the selection and the box down 10 units.
Selecting a cell and plowing it is a good way to move the cell. Load tut3f and select the cell tut3e. Point to the label ``point here'' and plow the selection with :plow selection. Notice that all connections to the cell have remained attached. The cell you select must be in the edit cell, however.
The plowing operation is implemented in a way that tries to keep your design as compact as possible. To do this, it inserts jogs in wires around the plow. In many cases, though, the additional jogs are more trouble than they're worth. To reduce the number of jogs inserted by plowing, type the command
From now on, Magic will insert as few jogs as possible when plowing, even if this means moving more material. You can re-enable jog insertion with the command
Load the cell tut3d again and try plowing it both with and without jog insertion.
There is another way to reduce the number of jogs introduced by plowing. Instead of avoiding jogs in the first place, plowing can introduce them freely but clean them up as much as possible afterward. This results in more dense layouts, but possibly more jogs than if you had enabled :plow nojogs. To take advantage of this second method for jog reduction, re-enable jog insertion (:plow jogs) and enable jog cleanup with the command
From now on, Magic will attempt to straighten out jogs after each plow operation. To disable straightening, use the command
It might seem pointless to disable jog introduction with :plow nojogs at the same time straightening is enabled with :plow straighten. While it is true that :plow nojogs won't introduce any new jogs for :plow straighten to clean up, plowing will straighten out any existing jogs after each operation.
In fact, there is a separate command that is sometimes useful for cleaning up layouts with many jogs, namely the command
where direction is a Manhattan direction, e.g., up, down, right, or left. This command will start from one side of the box and pull jogs toward that side to straighten them. Load the cell tut3g, place the box over the label ``put box here'', and type :straighten left. Undo the last command and type :straighten right instead. Play around with the :straighten command.
There is one more feature of plowing that is sometimes useful. If you are working on a large cell and want to make sure that plowing never affects any geometry outside of a certain area, you can place a boundary around the area you want to affect with the command
The box is used to specify the area you want to affect. After this command, subsequent plows will only affect the area inside this boundary.
Load the cell tut3h place the box over the label ``put boundary here'', and type :plow boundary. Now move the box away. You will see the boundary highlighted with dotted lines. Now place the box over the area labelled ``put plow here'' and plow up. This plow would cause geometry outside of the boundary to be affected, so Magic reduces the plow distance enough to prevent this and warns you of this fact. Now undo the last plow and remove the boundary with
Put the box over the ``put plow here'' label and plow up again. This time there was no boundary to stop the plow, so everything was moved as far as the height of the box. Experiment with placing the boundary around an area of this cell and plowing.