1: defined illegal all-zeroes
Exception, mcause = 2
16-bit illegal instruction: 0000
2: defined illegal all-ones
Exception, mcause = 2
32-bit illegal instruction: ffffffff
3: unimplemented CSR 0xfff
Exception, mcause = 2
32-bit illegal instruction: fff027f3
4: write to read-only CSR
Exception, mcause = 2
32-bit illegal instruction: f1101073
5: unimplemented instruction (F extension)
Exception, mcause = 2
32-bit illegal instruction: 00052087