Comment by the_biot
6 hours ago
Why the few closed-source components on the system? You mention the bus, USB PHY etc -- are those things harder to design than the CPU core?
6 hours ago
Why the few closed-source components on the system? You mention the bus, USB PHY etc -- are those things harder to design than the CPU core?
In general, things that are not strictly digital (PHYs, regulators, PLLs, ADCs) contain significant amounts of foundry IP that would be hard to release as open source. But also, some parts of the chip, for example the AXI bus fabric, were licensed simply as a risk reduction measure. If the bus fabric is bad, you've wasted millions of dollars on a mask set with little recourse. I tried to pull in some open source AXI fabrics and it wasn't pretty...a lot of rework required and even then still some bugs made it through to tape-out. Over time more and more of this can be opened but it all takes time, money, and people willing to do it.
Can I ask how bad it is with lower speed I/O? Less than 20Mbaud, so RS232, RS485, CAN, USB PD/Type-C, 10base-T, ...? The transceivers are rarely integrated, do they need different processes or do they just prefer flexible I/O pins or ...?
They are likely licensed IP.