HW_SCE_McuSpecificInit is quite slow

[WestfW]

It turns out that the HW_SCE_McuSpecificInit() function is pretty slow (~97000us on an RA4m1 (Arduino Uno R4)), causing code that naively calls it every time one wants a random number (for example) to be painful.

It would be nice if the function could detect that the SCE had already been initialized, and skipped most of the code.

See https://forum.arduino.cc/t/random-function-on-r4-terribly-slow/1342877/10 for example. where the Arduino random() function takes 90ms instead of 20us. (yes, this can also be fixed on the Arduino side. But it should not need to be fixed independently in every bit of code that uses the SCE.)

[michaelthomasj]

@WestfW ,
HW_SCE_McuSpecificInit() is used to initialize the TRNG. This only needs to be called once during hardware initialization. Your trng retrieval code only needs to invoke HW_SCE_RNG_Read(). I see that in your code you are calling both the init and read functions. Why?
The HW_SCE_McuSpecificInit() effectively performs a "reseeding" operation so it can be called anytime there is a need to reseed the TRNG. The reason why it takes time is that it takes thousands of samples of electrical noise and does a lot of processing to ensure that the results comply with NIST SP 800-90B specifications.
Additionally, while you could of course continue calling HW_SCE_RNG_Read(), you could also use the result of an initial call to seed a PRNG and get random numbers much faster.