Struct Config

#[non_exhaustive]
pub struct Config {
    pub disable_autocorrelation_test: bool,
    pub disable_crngt_test: bool,
    pub disable_von_neumann_balancer: bool,
    pub sample_count: u32,
    pub inverter_chain_length: InverterChainLength,
}

Configuration for the TRNG.

• Three built in entropy checks
• ROSC frequency controlled by selecting one of ROSC chain lengths
• Sample period in terms of system clock ticks

Default configuration is based on the following from documentation:

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RP2350 Datasheet 12.12.2

…

When configuring the TRNG block, consider the following principles: • As average generation time increases, result quality increases and failed entropy checks decrease. • A low sample count decreases average generation time, but increases the chance of NIST test-failing results and failed entropy checks. For acceptable results with an average generation time of about 2 milliseconds, use ROSC chain length settings of 0 or 1 and sample count settings of 20-25.

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Note, Pico SDK and Bootrom don’t use any of the entropy checks and sample the ROSC directly by setting the sample period to 0. Random data collected this way is then passed through either hardware accelerated SHA256 (Bootrom) or xoroshiro128** (version 1.0!).

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

disable_autocorrelation_test: bool

Bypass TRNG autocorrelation test

disable_crngt_test: bool

Bypass CRNGT test

disable_von_neumann_balancer: bool

When set, the Von-Neuman balancer is bypassed (including the 32 consecutive bits test)

sample_count: u32

Sets the number of rng_clk cycles between two consecutive ring oscillator samples. Note: If the von Neumann decorrelator is bypassed, the minimum value for sample counter must not be less than seventeen

inverter_chain_length: InverterChainLength

Selects the number of inverters (out of four possible selections) in the ring oscillator (the entropy source). Higher values select longer inverter chain lengths.

Trait Implementations

impl Clone for Config

fn clone(&self) -> Config

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Config

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Config

fn default() -> Self

Returns the “default value” for a type.

impl Copy for Config