ecc.P256 in embedded systems

I want to try ecc.P256 in embedded systems (using FreeRTOS) which have a hardware RNG.

I think I need to replace crypto.random with a customized one based on the hardware RNG. How to it? Modify crypto.zig?

/// This is a thread-local, cryptographically secure pseudo random number generator.
pub const random = &@import("crypto/tlcsprng.zig").interface;

After define cryptoRandomSeed, I still need to port the thread-local PRNG. Replace it seems
easier.

Using --single-threaded can eliminate references to __aeabi_read_tp.

Now, the remaining problem is the missing of __multi3 for u128 multiplication.

Next, I will try to rewrite mulxU64 to get rid of u128 multiplication.