I saw Santa’s thermal simulation demo at DAC – EEJournal

Just before Christmas at DAC 2021, as I walked through the nearly empty exhibit hall, Santa Claus leaned out of his booth and asked if I’d like to see his thermal simulation demo. Of course, it wasn’t really Santa Claus. It was David Ratchkov, the CTO of Anemoi Software.

David Ratchkov, CTO of Anemoi Software, dressed for DAC 2021. Photo credit: Anemoi Software

Santa’s demo involved an extremely detailed thermal simulation of an Apple M1 processor, which features a processor chip co-packaged with 16GB of LPDDR4 SDRAM on a System in Package (SiP) substrate, all sitting under a heatsink . You can see the Apple M1 processor chip and SDRAM chips shown in the image below.

The Apple M1 SiP incorporates a processor die (left) and two LPDDR4 SDRAMs (right). Image credit: Apple

The image below shows Anemoi Software’s thermal simulation of the Apple M1 SiP. The processor chip outline appears on the left and the co-packaged LPDDR4 SDRAMs appear on the right.

Thermal simulation of the Apple M1 SiP. Image credit: Anemoi Software

The Apple M1 processor die is an Arm-based SoC designed by Apple to serve as the CPU, GPU, and Neural Engine for the company’s new Macintosh computers and iPad Pro tablets. The M1 incorporates eight Arm processor cores. Four of these processor cores are high-performance processors and four are high-efficiency cores, following Arm’s big.LITTLE heterogeneous processing architectural model. SDRAMs provide unified memory to the CPUs, 8-core GPU, and Neural Engine.

Anemoi extracted thermal and electrical data to build this demo from published technical teardowns of the Apple M1. Therefore, these models are somewhat less detailed than they might be if actual design data were available. The thermal model in the Anemoi demo can be used for package-level thermal simulations, but you won’t get deeper insight into what’s going on at the block level in the chip, because the Anemoi model doesn’t is not sufficiently detailed to allow a more thorough thermal simulation. . However, this demo takes into account the detailed information available for the design of the PCB, including the metal layers of the board with their thermal conductivity, the solder balls used to attach the M1 BGA and their thermal properties, the IC package and the overall thermal properties. of the M1 processor chip.

As you can see in the image below, Anemoi’s thermal simulation shows the formation of a hot spot in the M1 chip and in the heatsink. Ratchkov pointed out that this level of detail is useful for the design of physical systems. For example, you can see from this simulation where you can best position a fan – at which end of the heatsink – to remove heat from co-located SDRAMs. DRAMs don’t like heat, so keeping them cool is a great idea. The Anemoi thermal simulator can take you much further in your design, given the right engineering data.

Heatsink thermal simulation for Apple M1 SiP. Image credit: Anemoi Software

Santa, er Ratchkov, shared another simulation with me to demonstrate the in-chip thermal simulation capabilities of his software. The second simulation he showed me was for a DEC Alpha processor. If you’re young enough, the name of this processor probably won’t ring a bell, and you might not even know what “DEC” stands for. “DEC” stands for “Digital Equipment Corporation”, which was the world’s largest and most important supplier of minicomputers for about three decades. In fact, DEC literally created the minicomputer market by introducing the first 18-bit PDP-1 minicomputer in 1959.

Following the introduction of the PDP-1, DEC introduced many families of PDP minicomputers with an assortment of data word widths and capacities, including the 12-bit PDP-8 families, the PDP-11 16 bits and culminating in the dominant world. 32-bit VAX minicomputer product family. I learned assembly language programming with Professor Philip Bevington on a DEC PDP-9 minicomputer. DEC only made 445 of these machines, and the PDP-9 minicomputer I learned to program controlled a synchrotron in the basement of the physics department at Case Western Reserve University.

However, in a classic case of Clayton Christensen’s innovator’s dilemma, DEC was wildly behind on the microprocessor part, even though the company had previously disrupted the mainframe computer market by introducing minicomputers. You would think that a company with this history and very many proven proprietary processor and ISA architectures would dive early and often into the microprocessor arena. You would be wrong. DEC ignored microprocessors and microcomputers for too long – until it was far too late.

Although DEC has dabbled in multi-chip, integrated implementations of its minicomputer architectures – notably the PDP-8 and PDP-11 machines – and a disastrously unsuccessful near-clone IBM PC and VT100 terminal emulator and some somewhat incompatible called DEC Rainbow 100, the company did not properly engage with microprocessors until 1989, nearly 20 years after the first commercial microprocessor appeared. That first machine, the short-lived DECstation 3100 workstation, was based on the 32-bit MIPS RISC architecture and could only be developed at a DEC skunkworks lab in Palo Alto, 3,000 miles and an entire continent from the mothership. from DEC in Maynard, Massachusetts. .

However, DEC’s true entry into microprocessors began with the DEC Alpha 21064, a 64-bit RISC processor based on DEC’s proprietary architecture and ISA. Alpha processors were DEC’s true entry into the workstation processor wars, and the Alpha family would outperform competing RISC microprocessors for a decade. But a high-performance processor is not enough. DEC continued to support the minicomputer, which turned out to be the wrong horse. The minicomputer business dried up under the onslaught of the microprocessor, and the ailing DEC was sold to Compaq Computer in 1998. All intellectual property for the DEC Alpha processor was sold to HP in 2001, where it then disappeared. DEC’s Alpha was too small, too late, despite its outstanding performance.

So why would Anemoi Software demonstrate its thermal simulator on a microprocessor that disappeared 20 years ago? This is precisely the question I put to Ratchkov. “Because there is a lot of detailed public information about this design,” he replied. Logic, for a demo.

Given the available data, Anemoi’s thermal simulation tools provide details of on-chip heat flows, as shown in the image below:

Thermal simulation of a 64-bit DEC Alpha microprocessor. Image credit: Anemoi Software

As you can see from the thermal graph above, there’s a particularly hot block on this DEC Alpha CPU chip. Curiously, the hot spot is the processor’s interrupt controller, according to Ratchkov.

Because you’re reading this article on EEJournal, I don’t do much to guess that thermal simulation might not be your thing. Often, mechanical or systems engineers are responsible for the design of thermal systems. Nevertheless, heat is an inevitable byproduct of moving many electrons at gigahertz rates. If you don’t handle this heat, chances are you’ll get dramatic system crashes, perhaps seconds or minutes after you flip the system switch.

So the trick is to find a thermal solution quickly, and that seems to be Anemoi Software’s hallmark. The company’s website lists four thermal case studies:

  • A QSFP-DD optical module
  • A matrix of GaN LEDs
  • A model to simulate different functional divisions for chiplet partitioning
  • An industrial design for an Arduino clone pcb

Build times for each of these case studies are under 20 minutes, and simulation time ranges from 5 to under 20 seconds. It looks like Anemoi’s simulation tools could indeed help you find thermal solutions quickly.

So next year at the DAC, when Santa asks if you want a demo, take the hint. Say yes.

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