103 lines
1.8 KiB
C
103 lines
1.8 KiB
C
/*
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* (c) Copyright 2018 by Coinkite Inc. This file is covered by license found in COPYING-CC.
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*/
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#include <string.h>
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#include "rng.h"
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#include "basics.h"
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#include "stm32l4xx_hal.h"
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// rng_setup()
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//
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void
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rng_setup(void)
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{
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if(RNG->CR & RNG_CR_RNGEN) {
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// already setup
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return;
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}
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// Enable the Peripheral
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__HAL_RCC_RNG_CLK_ENABLE();
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// Turn on feature.
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RNG->CR |= RNG_CR_RNGEN;
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// Sample twice to be sure that we have a
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// valid RNG result.
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uint32_t chk = rng_sample();
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uint32_t chk2 = rng_sample();
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// die if we are clearly not getting random values
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if(chk == 0 || chk == ~0
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|| chk2 == 0 || chk2 == ~0
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|| chk == chk2
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) {
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INCONSISTENT("bad rng");
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while(1) ;
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}
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}
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// rng_sample()
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//
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uint32_t
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rng_sample(void)
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{
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static uint32_t last_rng_result;
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while(1) {
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// Check if data register contains valid random data
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while(!(RNG->SR & RNG_FLAG_DRDY)) {
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// busy wait; okay to get stuck here... better than failing.
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}
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// Get the new number
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uint32_t rv = RNG->DR;
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if(rv != last_rng_result && rv) {
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last_rng_result = rv;
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return rv;
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}
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// keep trying if not a new number
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}
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// NOT-REACHED
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}
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// rng_buffer()
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//
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void
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rng_buffer(uint8_t *result, int len)
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{
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while(len > 0) {
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uint32_t t = rng_sample();
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memcpy(result, &t, MIN(4, len));
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len -= 4;
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result += 4;
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}
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}
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// rng_delay()
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//
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// Call anytime. Delays for a random time period to fustrate glitchers.
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//
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void
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rng_delay(void)
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{
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uint32_t r = rng_sample() % 8;
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uint32_t cnt = (1<<r);
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while(cnt) {
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asm("nop"); // need this to keep from being optimized away, check bootloader.lss
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cnt--;
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}
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}
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// EOF
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