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

The RP2350 datasheet (12.12.2) suggests sample count settings of 20-25 for an average generation time of about 2 milliseconds. On real hardware that setting only works while the core is busy: with the core sleeping in WFE (which is what the async executor does while waiting for the TRNG interrupt) the ring oscillator output becomes regular enough that every generation fails the autocorrelation or CRNGT health check.

Measured on a Pico 2 with the core sleeping, filling 1024 bytes:

sample_count	result
25	never completes
50	761 ms, many failed checks
100	19 ms
200	38 ms
1000	232 ms

The default is 200. Autocorrelation failures are retried automatically (up to 1000 times per block before panicking), so a marginal value degrades into slower generation rather than a hang. A value of 25 with a sleeping core fails every attempt and panics.

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 duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Config

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 Format for Config

where InverterChainLength: Format,

fn format(&self, f: Formatter<'_>)

Writes the defmt representation of self to fmt.