This has nothing to do with performance or hardware CPU development.
FPGA-specific soft cores like VexRiscv and NaxRiscv are immensely useful for anything involving state machine logic or glue code that you do not want to implement in-fabric.
Peripherals like on-chip MMCMs/PLLs, on-board I2C and SPI peripherals, etc. with complicated initialization routines or communication flows or sequencing are very easily handled in a soft CPU.
Soft CPUs can also be used like high-powered programmable in-circuit logic analyzers: without rebuilding a potentially massive FPGA bitstream, you can probe/observe/inspect, inject/alter any signals or buses you pipe to the CPU. VexRiscv is far more pleasant to use than any vendor ILA IP.
Soft CPUs also normally utilize FPGA LUTRAM/BRAM resources, enabling whatever program to run with hard real-time latency consistency.
this guy gets it - softcores are for giving people access to your IP without forcing them write their own RTL. it's literally the exact same thing as an embedded scripting language (i.e., vm interpreter.......) in a C/C++ program.
Also, soft cpus without strict performance and power requirements are really easy to implement with modern toolchains. In one quarter you can take an undergraduate who doesn't even know digital design and have them make a cpu core as a final project, and they can make a decent one.
HW is actually really hard. If you can use a soft core to simplify the overall design and suck up a bunch of peripheral logic it's probably a good idea. Then the engineers can spend their time focusing on getting the hard parts of the design correct.
FPGA-specific soft cores like VexRiscv and NaxRiscv are immensely useful for anything involving state machine logic or glue code that you do not want to implement in-fabric.
Peripherals like on-chip MMCMs/PLLs, on-board I2C and SPI peripherals, etc. with complicated initialization routines or communication flows or sequencing are very easily handled in a soft CPU.
Soft CPUs can also be used like high-powered programmable in-circuit logic analyzers: without rebuilding a potentially massive FPGA bitstream, you can probe/observe/inspect, inject/alter any signals or buses you pipe to the CPU. VexRiscv is far more pleasant to use than any vendor ILA IP.
Soft CPUs also normally utilize FPGA LUTRAM/BRAM resources, enabling whatever program to run with hard real-time latency consistency.