From: Keith Packard <keithp@keithp.com>
Date: Tue, 12 Sep 2017 20:40:06 +0000 (-0700)
Subject: chaoskey: Wait for input data to stabilize before using it
X-Git-Tag: 1.8.2~2^2~11
X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=commitdiff_plain;h=10d14146ef84fbe4670454bc0996854a4066cfea

chaoskey: Wait for input data to stabilize before using it

The ADC data takes a while to start working after power on; wait for
the range of input values to look reasonable before using the data.

Signed-off-by: Keith Packard <keithp@keithp.com>
---

diff --git a/src/drivers/ao_trng_send.c b/src/drivers/ao_trng_send.c
index b1227aaa..7cda053d 100644
--- a/src/drivers/ao_trng_send.c
+++ b/src/drivers/ao_trng_send.c
@@ -153,10 +153,20 @@ ao_trng_send(void)
 
 	ao_crc_reset();
 
-	ao_delay(TRNG_ENABLE_DELAY);
-
 	for (s = 0; s < AO_TRNG_START_WAIT; s++) {
-		if (ao_trng_get_cooked(buffer[0]))
+		int i;
+		uint16_t	min, max;
+		uint16_t	buf[AO_USB_IN_SIZE>>1];
+
+		ao_trng_get_raw(buf);
+		min = max = buf[0];
+		for (i = 1; i < (AO_USB_IN_SIZE>>1); i++) {
+			uint16_t v = buf[i];
+			if (v < min) min = v;
+			if (v > max) max = v;
+		}
+		/* Wait for at least 10 bits of range */
+		if ((uint16_t) (max - min) >= 1024)
 			break;
 		ao_delay(AO_MS_TO_TICKS(10));
 	}