3 ms·

The main distinction is that the 16-bit RISCV-C ISA exactly maps to existing 32-bit RISCV instructions, its implementation only occurs in the decode pipe stage

• bpye 5y ago
  The C extension is that, an extension. A RISC-V core with the C extension should still support the long encoding as well. There is no 16-bit variant specified, only 32, 64 and 128. There is an E version of the ISA with a reduced register set, but this is a separate thing.
  • brucehoult 5y ago
    You are mixing up integer register size and instruction length. RISC-V has variants with 32 bit, 64 bit, or (not yet fully specified or implemented) 128 bit registers. RISC-V has instructions of length 32 bits and, optionally but almost universally, 16 bit length.
    • Taniwha 5y ago
      The E version only has half as many registers
    • bpye 5y ago
      Ah yes, I misunderstood the original comment as implying that RISC-V C had 16 bit register length, rather than opcode length.