read_write_csr_field! {
    Hstatus,
    /// Supervisor Previous Virtualization mode
    spv,
    SPV: 7
}
```
and SPV was defined with the `csr_field_enum!`
```rs
csr_field_enum! {
    /// Supervisor Previous Virtualization mode
    SPV {
        default: WasVModeOff,
        WasVModeOff = 0,
        WasVModeOn = 1,
    }
}