Thursday, April 3, 2008

Atmel AT91SAM7S Overview

Atmel produces a number of ARM based devices in their portfolio of products. We had one laying around the lab so here we go as usual...

The device was a 48 pin QFP type package. We also purchased a sample of the other members of the family although the initial analysis was done on the AT91SAM7S32 part shown above. All pictures will relate to this specific part even though there is not a signifigant difference between the other members of this line except memory sizes.

After decapsulating the die from inside the QFP, we find a beautifully layed out 210nm 5 metal design! Thats right, 5 metal layers! Strangely enough, we would have thought this was a 220nm 5 metal but apparently Atmel doesn't have a .22um process so this is matching their .21um.

The core runs at 1.8v and allows 1.65v operation (thus it is their ATC20 process being used). The datasheet on the device can be found here. The 32KB Flash part also contains 8KB of SRAM (that's a lot of ram!).

Notice on this particular layout, there is CMP filler metal (e.g. dead metal, metal slugs that are not connected to anything floating in SIO2) covering almost the entire die.

The picture above actually has had the top 2 metal layers removed. Metal 5 (M5) being the highest with the CMP filler and some power planes. Metal 4 (M4) had additional power planes and routing wires.

With Metals 1-3 still present, we can get a nice overview of the floorplan now. We can see the Flash, Fuses, and SRAM clearly. The Flash has a solid coating of metal over the entire cell area which has become common from Atmel to prevent UV light attacks we suppose?

We can now label the areas on the original top metal overview photo. There is a small boot-rom loader present on the device as well and is explained in the manual.

The picture above shows some of the bits of this ROM.

In the above picture lay the configuration fuses. Single cell's of EEPROM type memory where any given cell can be set or cleared independently of another. Atmel layed them out very orderly as we see typically. It should be noted that these fuses are buried under 3 metal layers!

These cells were actually on Metal 1 and 2 but there are connections via Metal 3 as well.

There were additional power planes across the lower area of the photo from Metal 4 and 5 that cover those fuses however this isn't buying them any security if the actual lock bits were buried there. A laser can go right through it all keeping the power-bus in tact with a hole in it.

Finally, the Atmel part number of this die. The CMP filler is visible in this picture too.

In summary, this is a very well secured device. Fuses buried in a 5 metal layer design make the Microchip DSPIC's look like a piece of cake in comparision (They are 350nm 4 metal).

We didn't test this, but we are sure UV will set this fuses to a bad state if you can get the light to the floating gate since most all Atmel's behave this way.

Nice job Atmel!