When would you use a soft processor in an FPGA for embedded applications?

Soft processors are CPU cores implemented in FPGA programmable logic, offering flexibility for custom embedded systems. When to use: Need custom peripherals or instructions not in hard processors. Prototype ASIC designs. Low volume where hard processor cost not justified. Security applications requiring custom instruction encryption. Tight integration between CPU and custom logic. Multiple CPU instances for parallel processing. Popular soft processors: MicroBlaze (Xilinx) - 32-bit RISC, configurable features. Nios II (Intel/Altera) - 32-bit, economy to fast variants. RISC-V cores (VexRiscv, PicoRV32) - open-source, royalty-free. Design considerations: Resource usage (logic cells, memory blocks). Clock frequency (typically lower than hard processors). Debugging support (JTAG, trace). Software toolchain availability. Memory architecture (block RAM, external DDR interface). Trade-offs vs hard processors: Lower performance, higher power, more FPGA resources, but infinite flexibility.