In the latest issue of the MagPi magazine, out now, Raspberry Pi founder and CEO Eben Upton, and Principal Hardware Engineer Simon Martin, walk us through the design of the new Raspberry Pi Zero 2.
We caught up with Simon Martin, Principal Hardware Engineer at Raspberry Pi and Eben Upton, founder and CEO of Raspberry Pi.
Simon: “Raspberry Pi Zero 2 W is all about how much power you can pack into such a tiny space. It’s about just how much can we get from such a small form factor.
“Keeping that same form factor is important. An original Raspberry Pi Zero can be removed from a project and Raspberry Pi Zero 2 W can be plugged into its place. Any application that was there beforehand will get a boost from the processor performance.
“Instead of using the single-core processor that’s in the Raspberry Pi Zero, we’ve got a quad-core Cortex-A53 processor, which is similar silicon to the original Raspberry Pi 3 when that was announced.”
Eben: “There’s this whole question of ‘can we do it again?’ You can use Moore’s Law in two ways: you can take an amount of money and fill [Raspberry Pi] with more and more computing power, or you can take the current amount of computing power and deliver that at a lower and lower cost. And that’s what we did with Raspberry Pi 1 – we took a ten-year-old PC’s processing power and delivered it at around $30. And then we launched Raspberry Pi 2 in 2015 and, lo and behold, we’ve done the thing that everyone else does: we’ve picked a price point and filled it out with six times as much computing power using Moore’s Law.
“Raspberry Pi Zero is really the result of going ‘Aha! We should do the same thing as we did before.’ We should take a Raspberry Pi 1’s worth of computing power and we should use Moore’s Law to squeeze the price down.
“Every part on that board pays for itself. It’s a single-sided board, and it only has reflowable components; it doesn’t have any through-hole components. So it can all be manufactured simply and robotically.
“So, coming up to the sixth anniversary, and how to use everything we’ve learned from those five years, there’s this whole question of ‘can we do it again?’ And we’re delivering most of Raspberry Pi’s 3 power for not much more than half the price of a Raspberry Pi 3.
“The reality is that earlier this year people found out that Raspberry Pi knows how to make their own silicon [see, Raspberry Pi RP2040 in Raspberry Pi Pico – Ed]. Raspberry Pi Zero 2 W is not our own silicon, but we package silicon in unusual ways
Inside the package
Simon: “It’s also known as a ‘stacked package’. It’s the concept of putting more than one monolithic piece of silicon into a package to make a full system and package device. There’s a BCM2710A1 SoC (system on a chip) in there and half a gigabyte of DRAM. These are both gold-wire stitched to the substrate. That is then encapsulated to make the package. And so, by doing this, we can get two chips into the space of one.
“Because the chips are similar sizes you need to use a silicon interposer, or spacer, amongst the centre of the processor. Then, when you put the memory on top, it doesn’t squash the gold wires that connect the processor to the substrate. The memory is very sensitive, so there’s less desire to put anything on top of the memory, which is why the SoC goes on the bottom and the memory on top.
“The A53 was the highest performance chip that we’ve ever used that used wire bonding in the package, and Raspberry Pi Zero 2 W displays a considerable uptick in performance. Single-threaded performance is approximately 40% faster than a normal Raspberry Pi Zero. Obviously, this is quite cool, but if you do a benchmark of the single-core on a Raspberry Pi Zero and compare it to the quad-core of Raspberry Pi Zero 2 W, you get more than five times the performance. Real time performance is around three times the speed. A Raspberry Pi Zero takes around 90 seconds to boot into the GUI, whereas Raspberry Pi Zero 2 W takes around 30 seconds.
“It’s a small board, and if you are willing to help out by putting a heatsink on it, or if you put it in some sort of metal case where the heat can be drawn away from the chip, then it is possible to add voltage to the device so you can run it faster.” A Raspberry Pi Zero 2 W with a cooling solution can generally sustain 1.2GHz performance.”
Eben: “We use thick copper inside the board. So, effectively, we dissipate the heat throughout the board. So if you look at Raspberry Pi Zero 2 W with a thermal camera, you’ll see that it gets hot throughout the board. That’s because we’re using copper to move heat away from the CPU.
“The can [Wireless Lan enclosure] is a forward-looking thing to the days where people want to design this into things. We’ve got to be upfront: there’s not a huge amount of stock for the first year because ‘hey, there’s a global semiconductor shortage.’ Looking ahead, this is a product that’s going to be around for a long time, and we hope people will put it into product designs for OEMs.”