diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/drivers/ao_trng_send.c | 76 |
1 files changed, 62 insertions, 14 deletions
diff --git a/src/drivers/ao_trng_send.c b/src/drivers/ao_trng_send.c index 11f441f8..f8222993 100644 --- a/src/drivers/ao_trng_send.c +++ b/src/drivers/ao_trng_send.c @@ -25,32 +25,68 @@ static uint8_t trng_running; static AO_TICK_TYPE trng_power_time; -static void +/* Make sure there's at least 8 bits of variance in the samples */ +#define MIN_VARIANCE (128 * 128) + +#define DECLARE_STATS int32_t sum = 0, sum2 = 0 + +#define ADD_STATS(value) do { \ + sum += (value); \ + sum2 += (value) * (value); \ + } while(0) + +#define GOOD_STATS(i) (((sum2 - (sum * sum) / i) / i) >= MIN_VARIANCE) + +#define TRNG_ENABLE_DELAY AO_MS_TO_TICKS(100) + +static int ao_trng_send_raw(uint16_t *buf) { uint16_t i; uint16_t t; - uint16_t *rnd = (uint16_t *) ao_adc_ring; + uint16_t v; + + DECLARE_STATS; t = ao_adc_get(AO_USB_IN_SIZE>>1); /* one 16-bit value per two output bytes */ for (i = 0; i < AO_USB_IN_SIZE / sizeof (uint16_t); i++) { - *buf++ = rnd[t]; + v = ao_adc_ring[t]; + *buf++ = v; t = (t + 1) & (AO_ADC_RING_SIZE - 1); + + ADD_STATS(v); } + return GOOD_STATS(AO_USB_IN_SIZE / sizeof (uint16_t)); } -static void +static int ao_trng_send_cooked(uint16_t *buf) { uint16_t i; uint16_t t; uint32_t *rnd = (uint32_t *) ao_adc_ring; - t = ao_adc_get(AO_USB_IN_SIZE) >> 1; /* two 16-bit values per two output bytes */ + DECLARE_STATS; + + t = ao_adc_get(AO_USB_IN_SIZE) >> 1; /* one 16-bit value per output byte */ + for (i = 0; i < AO_USB_IN_SIZE / sizeof (uint16_t); i++) { - *buf++ = ao_crc_in_32_out_16(rnd[t]); - t = (t + 1) & ((AO_ADC_RING_SIZE>>1) - 1); + uint32_t v; + uint16_t v1, v2; + + /* Fetch two values in one operation */ + v = rnd[t]; + t = (t + 1) & ((AO_ADC_RING_SIZE >> 1) - 1); + + *buf++ = ao_crc_in_32_out_16(v); + + v1 = v; + v2 = v >> 16; + + ADD_STATS(v1); + ADD_STATS(v2); } + return GOOD_STATS(2 * AO_USB_IN_SIZE / sizeof (uint16_t)); } static inline int @@ -64,6 +100,8 @@ ao_trng_send(void) { static uint16_t *buffer[2]; int usb_buf_id; + int good_bits; + int failed = 0; if (!buffer[0]) { buffer[0] = ao_usb_alloc(); @@ -85,9 +123,9 @@ ao_trng_send(void) if (!trng_running) { AO_TICK_TYPE delay; - delay = trng_power_time + AO_MS_TO_TICKS(100) - ao_time(); - if (delay > AO_MS_TO_TICKS(100)) - delay = AO_MS_TO_TICKS(100); + delay = trng_power_time + TRNG_ENABLE_DELAY - ao_time(); + if (delay > TRNG_ENABLE_DELAY) + delay = TRNG_ENABLE_DELAY; /* Delay long enough for the HV power supply * to stabilize so that the first bits we read @@ -98,16 +136,26 @@ ao_trng_send(void) } if (ao_send_raw()) { ao_led_on(AO_LED_TRNG_RAW); - ao_trng_send_raw(buffer[usb_buf_id]); + good_bits = ao_trng_send_raw(buffer[usb_buf_id]); ao_led_off(AO_LED_TRNG_RAW); } else { ao_led_on(AO_LED_TRNG_COOKED); - ao_trng_send_cooked(buffer[usb_buf_id]); + good_bits = ao_trng_send_cooked(buffer[usb_buf_id]); ao_led_off(AO_LED_TRNG_COOKED); } ao_adc_ack(AO_USB_IN_SIZE); - ao_usb_write(buffer[usb_buf_id], AO_USB_IN_SIZE); - usb_buf_id = 1-usb_buf_id; + if (good_bits) { + ao_usb_write(buffer[usb_buf_id], AO_USB_IN_SIZE); + usb_buf_id = 1-usb_buf_id; + failed = 0; + } else { + failed++; + ao_delay(AO_MS_TO_TICKS(10)); + if (failed > 10) { + ao_usb_disable(); + ao_panic(AO_PANIC_DMA); + } + } } } |