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147f0df)
This detects broken hardware by making sure the standard deviation in
the raw values used to compute each buffer is at least 128.
Signed-off-by: Keith Packard <keithp@keithp.com>
static uint8_t trng_running;
static AO_TICK_TYPE trng_power_time;
static uint8_t trng_running;
static AO_TICK_TYPE trng_power_time;
+/* 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;
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++) {
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++) {
+ v = ao_adc_ring[t];
+ *buf++ = v;
t = (t + 1) & (AO_ADC_RING_SIZE - 1);
t = (t + 1) & (AO_ADC_RING_SIZE - 1);
+ return GOOD_STATS(AO_USB_IN_SIZE / sizeof (uint16_t));
ao_trng_send_cooked(uint16_t *buf)
{
uint16_t i;
uint16_t t;
uint32_t *rnd = (uint32_t *) ao_adc_ring;
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++) {
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 uint16_t *buffer[2];
int usb_buf_id;
{
static uint16_t *buffer[2];
int usb_buf_id;
+ int good_bits;
+ int failed = 0;
if (!buffer[0]) {
buffer[0] = ao_usb_alloc();
if (!buffer[0]) {
buffer[0] = ao_usb_alloc();
if (!trng_running) {
AO_TICK_TYPE delay;
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
/* Delay long enough for the HV power supply
* to stabilize so that the first bits we read
}
if (ao_send_raw()) {
ao_led_on(AO_LED_TRNG_RAW);
}
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_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_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);
+ }
+ }