2020-12-23 STM32F103 Pseudo Random Number Generator
- STM32F103 does no random number generator hardware but STM32F4 does
- So, we need implement the random number generator by software
Solution
- implement a pseudo random number generator
int seed; seed = seed + 271828192; seed = seed * 314159;
- but the seed is refer:
https://en.wikipedia.org/wiki/Linear-feedback_shift_register - give a initial value: 0xACE1u;
- The implemented reference code like this:
... int random_number_seed = 0xACE1u; ... int RND() { random_number_seed = random_number_seed + 271828192; random_number_seed = random_number_seed * 314159; return random_number_seed; } - but each time the random_number_seed will be initial,
- It will cause that the same sequence each time I reset the chip:
Random Number Test V0.01 1457057135 -973774463 -1937705265 79575585 -1180197841 -1988512063 -1234805361 ▒ Random Number Test V0.01 1457057135 -973774463 -1937705265 79575585 -1180197841 -1988512063 ▒ Random Number Test V0.01 1457057135 -973774463 -1937705265 79575585 -1180197841
- I use __no_init __root before variables, variables will not init again if I reset system. It keep the values before reset.
- Rewrite program as follows:
... __no_init __root int random_number_seed; // Do Not Assign Value ... void Initial_RandomNumberSeed() { // 初始化 Random Number Seed if (random_number_seed == 0) random_number_seed = 0xACE1u; } ... int RND() { random_number_seed = random_number_seed + 271828192; random_number_seed = random_number_seed * 314159; return random_number_seed; } - Then, the output as follows:
Random Number Test V0.01 1457057135 -973774463 -1937705265 79575585 -1180197841 -1988512063 -1234805361 ▒ Random Number Test V0.01 1171481418 416394678 ▒ Random Number Test V0.01 -1540031606 829907318 1596603338 ▒ Random Number Test V0.01 -9376458 1087120394 Random Number Test V0.01 1884639478 -1529629622 236686518 -1130763126 2065342582 ▒ Random Number Test V0.01 1394068682 1846119478 283530506 771706870 1077839178 -1905071178 ▒ Random Number Test V0.01 284777866 1799053174 1552932298 -1534088394 -367327734 -1694052618 ▒ Random Number Test V0.01 844355146 731368118 -1550627190 731487862
Reference
- 1, keep ram value when NVIC_SystemReset(); (2016-05-13)
- 2, Default values for variable stored in SRAM (2018-09)
- 4, How generate REAL random number using STM32 MCU? (2012-02-10)
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