But then I wondered -- what actually was the motivation for this all out Open Source SoC?
There have been a few projects like this posted to Slashdot over the years. For some people, it's like climbing Mount Everest -- "because it's there". Some people want to extend the open hardware community down into chip design, possibly encouraging new start-up companies. (lowRISC seems to be in this category.) And some people think the semiconductor industry is a stagnant patent-choked wasteland in need of a Linux-style revolution. (These people are idiots, and do not know anything about hardware manufacturing or the semiconductor industry.)
The big thing I don't understand is why they all want to make chips with high-performance CPUs with tons of modern peripherals. Okay, I do understand -- they want to run Linux on their product. But what's wrong with making an AVR clone? Surely it would be much easier and much cheaper to make an 8- or 16-bit CPU with a few low-end comm peripherals on an older process? Is making a fully open hardware Arduino somehow less of an accomplishment?
Regardless, none of these projects have succeeded yet, because making an SoC is much harder than making software. From easiest to hardest, the main obstacles to making an open IC product are: development skills, design tools, prototyping and manufacturing costs, testing, and logistics. I'm not an expert on the full process, but I can try to give an overview:
* Development skills: Designing high-quality digital integrated circuits, even with an HDL, is not trivial. You need people with EE or CE training, not just basic programming skills. Hardware has non-ideal behavior that must be accounted for in the design. It's also not cheap, so the design needs to (mostly) work the first time. This means you need real expertise, not just random volunteers. lowRISC has some experienced people (although not in IC design?) running it, and they're hiring a couple of EE Ph.Ds right now.
* Design tools: You can edit an HDL with a text editor, but physical design and simulation require nasty, expensive, proprietary software packages from companies like Cadence or Mentor Graphics. These are not cheap, so you won't be running a copy at home. Your work will happen at an organization with money, like a university or corporation. lowRISC is a nonprofit associated with the University of Cambridge, so they can probably negotiate lower rates.
* Prototyping and manufacturing costs: You can prototype an IC design on an FPGA, but large FPGAs are pretty expensive. Again, you'll need money for this, thousands of dollars per FPGA board at least. At some point, you'll want to make real hardware. You might be able to get a few prototype units for tens of thousands of dollars, but for real manufacturing in a modern process you'll need a proper mask set. This will probably be on the order of $500k. Small revisions (metal-only) will cost perhaps a tenth as much. If you need to move transistors around, you'll have to go through the physical design process and pay the full ~$500k again. An important side effect of this is that most design bugs will be fixed in the physical layout, not the HDL. This requires expertise, and you'll need to design for the possibility in advance. After all that, you'll have to spend thousands of dollars per wafer for manufacturing, plus more for testing (see below). lowRISC's nonprofit/academic status will help reduce these costs, and obviously they're getting funding from Cambridge and maybe their founders.
* Testing: Even if your design is perfect (and it never is), you will need to test and qualify the hardware before you can sell it. This is where open IC projects fall flat, because nobody even talks about testing. You'll need to include test features like ATPG in your design, probably using even more expensive design tools. You'll also need to write test cases for functional verification, and generate test patterns for your automated test equipment (ATE). Once you've made the tests, you'll need equipment and personnel to run them. This costs more money. For qualification (making sure the hardware doesn't break the moment it gets out the door), you'll need to make and test (at least) thousands of units, preferably from multiple wafers with process variations. You'll also need to work on test time reduction and yield improvement once you reach production. lowRISC does not mention testing at all. They do say they plan to go from test chip to production silicon in one year, and that they're expecting to "yield around 100-200k good chips per batch [of ~25 wafers]". So maybe they have a plan, or maybe they're paying someone else to handle all the DFT design and testing aspects. (I'm not sure I'd call that "open hardware", though.) Since this is a nonprofit/academic project, their early customers may not expect any real quality assurance.
* Logistics: Once you're shipping units in production, you need to do all the boring (yet vital) business stuff like managing your cash flow, making sure orders ship on time, handling customer complaints, adjusting your price over time, making sure you don't break any laws, etc. This requires a full-time staff, at which point you're not really a community project anymore. lowRISC is already an organization with a staff, so this shouldn't be a huge problem for them.
They have very little information posted so far (not even a feature list), but lowRISC seems to have a few things going for them. They're not begging for money. They can get academic discounts. They're aware that they need serious expertise. And they're only aiming for the moon instead of the Andromeda Galaxy. I'm not holding my breath, but they might have a real chance. I wish them the best of luck.