src/machine/machine_stm32_rng.go


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

//go:build stm32 && !(stm32f103 || stm32l0x1)
// +build stm32,!stm32f103,!stm32l0x1

package machine

import "device/stm32"

var rngInitDone = false

const RNG_MAX_READ_RETRIES = 1000

// GetRNG returns 32 bits of cryptographically secure random data
func GetRNG() (uint32, error) {
	if !rngInitDone {
		initRNG()
		rngInitDone = true
	}

	cnt := RNG_MAX_READ_RETRIES
	for !stm32.RNG.SR.HasBits(stm32.RNG_SR_DRDY) {
		cnt--
		if cnt == 0 {
			return 0, ErrTimeoutRNG
		}
	}

	ret := stm32.RNG.DR.Get()
	return ret, nil
}