Microwatt goes multiprocessor

It's been awhile since we dropped in on Microwatt, the OpenPOWER VHDL softcore. Microwatt now runs on multiple FPGA boards or can be run (slowly) in simulation, and is capable of booting Linux. Raptor uses Microwatt for the Arctic Tern soft BMC. Although it still doesn't support vector instructions, recent commits have added an FPU and many of the standard special-purpose registers, and the newest ones now add support for SMP.

The newest pull request, currently to be committed, allows more than one processor core to be created by adding an NCPUS option to soc.vhdl. These cores can be debugged separately with JTAG and have the same view of memory and the same timebase value, and can be individually activated. For interrupts, they each have their own presentation controller in the XICS.

Although Microwatt cores are currently of only modest performance, more cores — if you have the space — can certainly improve its throughput and the range of applications it could be practical for. Unfortunately, we've still yet to hear anything new about the Solid Silicon S1 or how libre Power11 will end up being. Hopefully as the Microwatt design gets more efficient, at least the very smallest Power ISA systems will now have some additional flexibilities to work with.