RNG — Random number generator

The Random number generator (RNG) generates true non-deterministic random numbers based on internal thermal noise that are suitable for cryptographic purposes. The RNG does not require a seed value.

Figure 1. Random number generator

The RNG is started by triggering the START task and stopped by triggering the STOP task. When started, new random numbers are generated continuously and written to the VALUE register when ready. A VALRDY event is generated for every new random number that is written to the VALUE register. This means that after a VALRDY event is generated the CPU has the time until the next VALRDY event to read out the random number from the VALUE register before it is overwritten by a new random number.

Bias correction

A bias correction algorithm is employed on the internal bit stream to remove any bias toward '1' or '0'. The bits are then queued into an eight-bit register for parallel readout from the VALUE register.

It is possible to enable bias correction in the CONFIG register. This will result in slower value generation, but will ensure a statistically uniform distribution of the random values.

Speed

The time needed to generate one random byte of data is unpredictable, and may vary from one byte to the next. This is especially true when bias correction is enabled.

Registers

Table 1. Instances
Base address Peripheral Instance Description Configuration
0x4000D000 RNG RNG

Random number generator

    
Table 2. Register Overview
Register Offset Description
TASKS_START 0x000

Task starting the random number generator

  
TASKS_STOP 0x004

Task stopping the random number generator

  
EVENTS_VALRDY 0x100

Event being generated for every new random number written to the VALUE register

  
SHORTS 0x200

Shortcut register

  
INTENSET 0x304

Enable interrupt

  
INTENCLR 0x308

Disable interrupt

  
CONFIG 0x504

Configuration register

  
VALUE 0x508

Output random number

  

SHORTS

Address offset: 0x200

Shortcut register

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Id                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Id RW Field Value Id Value Description
A RW

VALRDY_STOP

    

Shortcut between VALRDY event and STOP task

See EVENTS_VALRDY and TASKS_STOP

     

Disabled

0

Disable shortcut

     

Enabled

1

Enable shortcut

 

INTENSET

Address offset: 0x304

Enable interrupt

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Id                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Id RW Field Value Id Value Description
A RW

VALRDY

    

Write '1' to Enable interrupt for VALRDY event

See EVENTS_VALRDY

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

 

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Id                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Id RW Field Value Id Value Description
A RW

VALRDY

    

Write '1' to Disable interrupt for VALRDY event

See EVENTS_VALRDY

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

 

CONFIG

Address offset: 0x504

Configuration register

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Id                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Id RW Field Value Id Value Description
A RW

DERCEN

    

Bias correction

     

Disabled

0

Disabled

     

Enabled

1

Enabled

 

VALUE

Address offset: 0x508

Output random number

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Id                                                 A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Id RW Field Value Id Value Description
A R

VALUE

  

[0..255]

Generated random number

 

Electrical specification

RNG Electrical Specification

Symbol Description Min. Typ. Max. Units
IRNG

Run current, CPU sleeping.

 500 µA
tRNG,START

Time from setting the START task to generation begins. This is a one-time delay on START signal and does not apply between samples.

 128 µs
tRNG,RAW

Run time per byte without bias correction. Uniform distribution of 0 and 1 is not guaranteed.

 30 µs
tRNG,BC

Run time per byte with bias correction. Uniform distribution of 0 and 1 is guaranteed. Time to generate a byte cannot be guaranteed.

 120 µs
Documentation feedback | Developer Zone | Updated 2021-11-08