pico_rand

Functions
void	get_rand_128 (rng_128_t *rand128)
	Get 128-bit random number. More...
uint64_t	get_rand_64 (void)
	Get 64-bit random number. More...
uint32_t	get_rand_32 (void)
	Get 32-bit random number. More...

Detailed Description

Random Number Generator API

This module generates random numbers at runtime utilizing a number of possible entropy sources and uses those sources to modify the state of a 128-bit 'Pseudo Random Number Generator' implemented in software.

The random numbers (32 to 128 bit) to be supplied are read from the PRNG which is used to help provide a large number space.

The following (multiple) sources of entropy are available (of varying quality), each enabled by a #define:

• The Ring Oscillator (ROSC) (PICO_RAND_ENTROPY_SRC_ROSC == 1): PICO_RAND_ROSC_BIT_SAMPLE_COUNT bits are gathered from the ring oscillator "random bit" and mixed in each time. This should not be used if the ROSC is off, or the processor is running from the ROSC.

  Note

  the maximum throughput of ROSC bit sampling is controlled by PICO_RAND_MIN_ROSC_BIT_SAMPLE_TIME_US which defaults to 10us, i.e. 100,000 bits per second.

• Time (PICO_RAND_ENTROPY_SRC_TIME == 1): The 64-bit microsecond timer is mixed in each time.
• Bus Performance Counter (PICO_RAND_ENTROPY_SRC_BUS_PERF_COUNTER == 1): One of the bus fabric's performance counters is mixed in each time.

Note

All entropy sources are hashed before application to the PRNG state machine.

The first time a random number is requested, the 128-bit PRNG state must be seeded. Multiple entropy sources are also available for the seeding operation:

• The Ring Oscillator (ROSC) (PICO_RAND_SEED_ENTROPY_SRC_ROSC == 1): 64 bits are gathered from the ring oscillator "random bit" and mixed into the seed.
• Time (PICO_RAND_SEED_ENTROPY_SRC_TIME == 1): The 64-bit microsecond timer is mixed into the seed.
• Board Identifier (PICO_RAND_SEED_ENTROPY_SRC_BOARD_ID == 1): The board id via pico_get_unique_board_id is mixed into the seed.
• RAM hash (PICO_RAND_SEED_ENTROPY_SRC_RAM_HASH (PICO_RAND_SEED_ENTROPY_SRC_RAM_HASH): The hashed contents of a subset of RAM are mixed in. Initial RAM contents are undefined on power up, so provide a reasonable source of entropy. By default the last 1K of RAM (which usually contains the core 0 stack) is hashed, which may also provide for differences after each warm reset.

With default settings, the seed generation takes approximately 1 millisecond while subsequent random numbers generally take between 10 and 20 microseconds to generate.

pico_rand methods may be safely called from either core or from an IRQ, but be careful in the latter case as the calls may block for a number of microseconds waiting on more entropy.

Function Documentation

get_rand_128()

void get_rand_128

(

rng_128_t *

rand128

)

Get 128-bit random number.

This method may be safely called from either core or from an IRQ, but be careful in the latter case as the call may block for a number of microseconds waiting on more entropy.

Parameters

rand128

Pointer to storage to accept a 128-bit random number

get_rand_32()

uint32_t get_rand_32

(

void

)

Get 32-bit random number.

This method may be safely called from either core or from an IRQ, but be careful in the latter case as the call may block for a number of microseconds waiting on more entropy.

Returns

32-bit random number

get_rand_64()

uint64_t get_rand_64

(

void

)

Get 64-bit random number.

This method may be safely called from either core or from an IRQ, but be careful in the latter case as the call may block for a number of microseconds waiting on more entropy.

Returns

64-bit random number