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esp32s2: Enable 8M clock source for RNG also

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Either of these options is sufficient to pass dieharder test suite with
bootloader random output, having both enabled is a bonus.
This commit is contained in:
Angus Gratton 2020-05-28 17:44:26 +10:00
parent 699742acc6
commit 9311b1e7be
1 changed files with 9 additions and 0 deletions
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9
components/bootloader_support/src/bootloader_random_esp32s2.c
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@ -39,6 +39,10 @@ void bootloader_random_enable(void)
periph_module_enable(PERIPH_RNG_MODULE);
#endif // BOOTLOADER_BUILD
// Enable 8M clock source for RNG (this is actually enough to produce strong random results,
// but enabling the SAR ADC as well adds some insurance.)
REG_SET_BIT(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_DIG_CLK8M_EN);
// Enable SAR ADC to read a disconnected input for additional entropy
SET_PERI_REG_MASK(DPORT_PERIP_CLK_EN0_REG,DPORT_APB_SARADC_CLK_EN);
@ -94,4 +98,9 @@ void bootloader_random_disable(void)
SET_PERI_REG_MASK(DPORT_PERIP_CLK_EN0_REG, DPORT_APB_SARADC_CLK_EN);
SET_PERI_REG_BITS(SENS_SAR_POWER_XPD_SAR_REG, SENS_FORCE_XPD_SAR, 0, SENS_FORCE_XPD_SAR_S);
CLEAR_PERI_REG_MASK(APB_SARADC_CTRL2_REG, APB_SARADC_TIMER_EN);
/* Note: the 8M CLK entropy source continues running even after this function is called,
but as mentioned above it's better to enable Wi-Fi or BT or call bootloader_random_enable()
in order to get a secondary entropy source.
*/
}