Often it can be very handy to have a CPU in an FPGA. Though some are sold with an integrated CPU, most are not. A popular option is to use a so called Softcore CPU, a CPU that is implemented in the FPGA’s logic. I decided to have a look at a few popular and some less popular ones to see how easy they are to use, how fast they are and which might be a good choice for a project.
I have a few requirements any CPU must meet:
1. There must be a GCC or LLVM compiler available
2. No vendor specific CPU, a CPU should run on all FPGA’s
If possible, a simple ready to go SoC with Uart, Timer and GPIO is nice, but no requirement.
Not that many requirements, so after some googling I found the following options:
- S1 Core
- Swerv EH1
Sadly the S1 core and Swerv EH1 did not fit in my Arty board. I tried getting them small enough, but I need the Arty A7-100, so if anyone wants to sponsor me ;)
This still means 6 in total, and there are most likely some other good options as well that I missed.
From looking at the documentation, my gut feeling says that VexRiscv, LEON3 and Neo430 are going to be the nicest to use. I would say that the Microwatt, ZPU and the PicoRV32 are more hobby oriented. But let’s not get ahead of ourselves, each core will be looked at in more detail.Continue Reading