Does MISA.B control zba/zbb/zbc/zbs?

[Joseph Rahmeh]

We are implementing the bit-manipulation extension, do we then implement the B bit in the MISA CSR? The privileged spec says that the B bit is reserved and must return zero on read.

[Paul Donahue]

No. misa.B was previously going to be used for the B extension but it is now (in the ratified priv spec) a reserved bit. There is no B extension, just a group of Zb* extensions which are not related to the B bit.

[Joseph Rahmeh]

Thanks for the quick reply. Closing.