Archive for the ‘ Utopium ’ Category

Utopiums are back

After months being manufactured, the Utopiums are back! I will explain more about what they are in another post, but for now here are some photos.

Here are the packaged chips (20 of).

They also send you the remaining unpackaged dies. These have an excellent ability of confusing the camera’s auto focus.

The full die is 5mm by 3mm.

And this is what they look like under a microscope. They do get dirty very quickly when exposed to a dusty room.

On the bottom right of the chip logo are the thank-yous. The Tux and the Fedora logo are about 0.5 mm tall (perhaps the smallest ever?). You can see the diffraction grating giving a nice secondary colour.

At different angles, they look very different.

And here is a wise comment left by the one of the Async symposium reviewers.

I am still testing the beast, but it does work. It has executed a number of programs and the wagging slices do become by-passable. The biggest worry was the reset as that is quite complicated, but it seems fine. I will open source the design and the tool set some time next month.

Utopium test board

I was expecting the Utopium to come back any minute now, but it appears when the fab says 11 to 12 weeks, they don’t mean from the tape-out date, they mean from some other date a month after (Grrrr). As I was expecting it this week, I made a board that it can sit in. If it works I will make a proper PCB with connections to peripherals, but in the mean time what I need is a platform from which I can observe and control every pin on the chip. Here are the ingredients.

This used to be Matt’s desk but it has been converted into my hardware geekery desk. The scope is a fantastically expensive one that I am currently using as a voltmeter.

First job was making a cable. The I have plenty of these IDE cables around. Splitting it into two and clipping some connectors, I now have 40 way to two 20 ways that fit into Jim’s lab board.

This is version 3 of the Jim’s lab board. The first one was back in 1999 when I started writing KMD. These boards have a default FPGA configuration which memory maps the I/O pins. This is ideal if you don’t to get into FPGA development just to get something simple going. Everything can be controlled from software running on the ARM.

I’m sure we probably have may of these three pin connectors in the electronics cabinets, but since I had an old broken motherboard on the desk, I thought this was easier.

The solder used on motherboards has a much higher melting point which can be annoying when removing larger though board components, but this wasn’t that bad. For large components I recommend placing the board onto an electric kitchen hob hotplate, then after a minute, turning it over and hitting to make all the parts fall out (ventilated room and a mask is probably in order here).

For signal wiring I use a Vero pen. These are fantastic. They are very thin, insulated wires which you wrap a couple times around the connected pins, then use solder to melt off the insulation. The insulation makes the solder point a bit dirty, but meh, they’re connected. Just dont show it to engineers, they suck their teeth and explain how they wouldn’t do it that way and start sentences with the words “Back in my day…”.

The danger of the Vero wire is that you can get it too hot while soldering a point near it and form a connection. The power connections were made using thicker wire.

And nearly one hundred solder points later we have a simple board. The ZIF socket is for a 48 pin DIL. These look weirdly long, as will the Utopium, when it comes back.

Happily connected to the Jim board, and tested for any shorted connections. I did this by flipping the I/O pins about. If you get values stuck half way between the rails, then something is shorted. This happened to me, but luckily the FPGA was quite robust to short connections and it worked fine after correcting it.

Here is a PIC in the socket. You can see how much longer the Utopium will be.

Well, one month left until she comes back. Can’t wait.

Corner cells

In chip design, there is generally a “pad ring” (a ring of external connections) around the edge of the design. Each of the four edges has a series of wires connecting each pad to the next. This is fine for edges, but when you have to go round a corner, you need a corner cells to connect the wires from the horizontal row of pins to the vertical set.


These YA28SHB and XMHB are names of pad cells. First thing you may notice is that these cells are just red boxes and we cannot see inside. That is because we are not given the “cell internals”, in case we release some company secrets of their construction to competitors. We can use the cells but we cannot see how they function. This is normally fine but then it can cause some embarrassing failures. Yesterday we received a design rule check report from IMEC (the people who are taking care of the manufacturing). Included was this screen-shot.


You can see they get the luxury of being able to see the cell internals and it makes spotting some errors trivial. There are blue wires along the bottom edge, and these need to be connected to the set along the right edge. This is where we placed our corner cell, which turns all the wires by 90 degrees. Unfortunately the cell is incorrectly rotated and is not connecting to either set of wires. This was spotted by IMEC and we have now corrected this, but if it wasn’t it would have been a complete failure.

Two things to take from this. Firstly, giving out cell internals of some cells is useful to spot errors. I doubt there are many engineering secrets involved in a set of wires turned through 90 degrees. The second is to never assume that just because the pins are positioned and rotated starting from the bottom left going clockwise, it will be the same for the corner cells. In this case the corner cells start in the top right.

Fixed this and some minimum area issues and taped out (yet) again this afternoon.

Making a silicon chip logo

utopium_bonding_diagramHistorically, when manufacturing silicon designs, it used to be a bit of engineering fun to add a little non logo or a cute little image to the design. There are some fantastic examples of this available at Silicon Zoo. Nowadays, it is actually an essential part of the process as a large visible logo makes it easy to spot the different designs on multi project wafers, and is a requirement by the people who do the wire bonding to make sure the chip is correctly oriented. The in-line image is what we send to the people connecting the silicon to the chip package using rather small wires. In the diagram there is the Utopium chip package with a, to-scale, die plot of the silicon with the logo clearly visible and all the wire connections we need. This serves two uses, firstly it shows the orientation of the chip, and secondly it makes sure we don’t have any crossing wires.

This time we48pinDIL are using a reather simple 48 pin DIL package which a rather retro package with relatively few pins, but it makes life easier when making the test board.

Making the Logo

origial_catSo, onto making a chip logo. You first need two pieces of information, the minimum top level metal size (in my case the level 8 metal layer for the UMC 130nm process has a minimum width of 1.5um) and the size of the logo (for this example I will make one 0.75mm x 0.6mm). Using those numbers you can determine the size of your canvas (“750um x 600um” / 1.5um is roughly 500 x 400 pixles).

Next, create an image in Gimp (or equivalent) of your required size. Use black on white. Here is our example cat. This now needs to be saved as a .pnm file. When the “Data formatting” dialog pops up, select Ascii. Keep the gimp window open as we will need it later.

Now we need to run pnm2cif on the file. This was written by Andrew Bardsley and is released under the “Whatever you like” licence (GPLv2+ or BSD). Download it to the same directory as the image, and run:

> ./ <pnm-image-filename> <cell-name> <scalar> <layer-name>

The pnm file is the image, the cell-name will be the name of the new cell, the scalar is the size of the feature size, and the layer-name is the name of the metal layer used. In our case these are:

> ./ cat_logo.pnm cat_logo 1500 ME8

The scalar of 1500 is because the minimum feature size in nanometres, and ME8 is the name of the top level metal layer.

imported_catHopefully this has now produced  a .cif file which can be imported into your layout editor. We will use Cadence Virtuoso for this. From ICFB select File -> Import -> CIF, enter the filename and set the Scale UU/DBU to 0.001 micron (the 1nm we used as a base unit) and select the library which it should be imported into. The two warnings are normal. Open up the newly imported cell and make sure it is the correct size.

Because the design is made of metal slices which are not connected we need to merge them all into one. Select all (Ctrl+A) and merge (Shift+M). Now that all the metal slices are merged, the logo is ready to go? Well, no, the design first has to pass the DRC rules.

Passing DRC

drc_failAt this stage the design is covered with “Design Rule Check” faults. The most common ones are two pixels meeting at corners, like shown in the in-line image. This essentially creates an infinitely thin wire (the fabrication folk don’t like making these). So, back to gimp, to manually fix these up with a pen. If you tried to use a dithered image, at this point you will be admitting defeat and moving to a simpler design.

copy_pixelsThe next thing to fix is the maximum wire thickness. This is 30um which is 20 pixels. In order to break up the design and make sure there are no blocks thicker than 20 pixels, we first select a strip of pixels with one white pixel and 20 black. Copy this to the clipboard. Select the bucket fill tool, select pattern fill (pattern from clipboard should be selected as default) and click any large blocks. Selecting two pixels, one white and one black, and doing a flood fill creates a striped pattern which creates a diffraction grading. Get someone with a physics degree to work out the size of the lines to create (I guessed).

sliced_catNow we need to repeat the whole process and run DRC to make sure there are no faults. It will probably take several attempts before all the errors are removed. At the foundry, in order to meet some other design rules, the process will do two additional things which may ruin the design: slotting (also known as cheesing) and metal fill. Slotting involves punching holes in all large metal areas, and metal fill makes sure a certain range of the area of the chip is covered with metal. To stop these from ruining the design, there usually is a layer you can add (in our case it was M8_CAD). This is acceptable only because the metal is non functional and thus does not have to adhere to some design rules. Make sure the design does not cover the whole chip, so there is enough space for the fab to metal fill.

And then you’re done. The Utopium logo looks like this. Make sure you get permission to use any copyrighted artwork or trademarked designs (I did, thanks Fedora for letting me use your logo).