Meaning of misa.B in relationship to Zba, Zbb, Zbc and Zbs extensions

[Arjan Bink]

How does the B bit in the MISA CSR relate to the Zba, Zbb, Zbc and Zbs extensions? If a core implements the Zba, Zbb, Zbc and Zbs extensions should it then also set MISA.B to 1? What if a core for example only implements the Zbb extension?

[zhonghochen]

Here is a related issue
riscv/riscv-isa-manual#907