rng doesn't check RNG_SR

[NicolaiSoeborg]

It seems like the get_rng command doesn't check the "RNG status register" (RNG_SR).

From page 659 of the reference manual [0]:

When a noise source (or seed) error occurs, the RNG stops generating random numbers and sets to “1” both SEIS and SECS bits to indicate that a seed error occurred. If a value is available in the RNG_DR register, it must not be used as it may not have enough entropy.

The check seems to be done in the embedded code at: https://github.com/solokeys/solo/blob/master/targets/stm32l432/src/rng.c#L28 but why is the check and'ing with 0x66 ? The documentation says that CEIS and SEIS are bit 5 and 6, so shouldn't the check be RNG->SR & 0x60 or RNG->SR & 0x06 depending on endianness?).

[0] RM0394: https://www.st.com/content/ccc/resource/technical/document/reference_manual/group0/b0/ac/3e/8f/6d/21/47/af/DM00151940/files/DM00151940.pdf/jcr:content/translations/en.DM00151940.pdf

[conorpp]

It's only checking one byte, so endianness isn't an issue. 0x60 checks the CEIS and SEIS bits (bits 5, 6), and the 0x06 checks SECS and CECS (bits 1, 2).

I suppose RNG->SR & 0x60 would be sufficient, since they indicate that either SECS or CECS would be set. But might as well check all at once (RNG->SR & 0x66).

[nickray]

Wrong repo.