+ case CSR_MISA: {
+ if (!(val & (1L << ('F' - 'A'))))
+ val &= ~(1L << ('D' - 'A'));
+
+ // allow MAFDC bits in MISA to be modified
+ reg_t mask = 0;
+ mask |= 1L << ('M' - 'A');
+ mask |= 1L << ('A' - 'A');
+ mask |= 1L << ('F' - 'A');
+ mask |= 1L << ('D' - 'A');
+ mask |= 1L << ('C' - 'A');
+ mask &= max_isa;
+
+ isa = (val & mask) | (isa & ~mask);
+ break;
+ }