From: Geert Uytterhoeven > Sent: 14 February 2022 14:26 ... > I'm afraid you missed one important detail. You wrote: > > > On every platform, random_get_entropy() is connected to get_cycles(), > > except for three: m68k, MIPS, and RISC-V. > > The default implementation in include/asm-generic/timex.h is: > > static inline cycles_t get_cycles(void) > { > return 0; > } > > Several architectures do not implement get_cycles(), or implement it > with a variant that's very similar or identical to the generic version. Add to the list nios2 and old x86 (I think rdtsc is a pentium instruction) I can't see it in my 386 book, and i don't think 486 added it. I'm not sure if/when sparc added one. I don't remember it being there in the late 1980s. nios2 (soft cpu on Altera/Intel fpga) is annoying. There is a 'read control register' instruction and plenty of space ones. But you can't define your own and one isn't a clock counter. You can add one as the result of a custom instruction. (Even the same custom instruction that does byteswap.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)