Fix gpio/dht_sensor

[keytouch]

As I was testing, without prior sleep_us(2) before waiting for low signal, it turned out to be Bad data.
Tested on DHT11, I don't own a DHT22, but the line protocol should be the same.

• sleep_us(2) before waiting for low signal

• check iteration variable j to avoid out of bound write on data[5]

• flip last directly instead of polling again

• 1 bit is 70us and 0 bit is about 26-28us, fix the check on polling count

[github-actions]

Please do not submit against master, use develop instead

[lurch]

Changes look reasonable to me, but I don't have a DHT-11 or DHT-22 sensor to check that the code still works correctly.

[keytouch]

I purchased a DHT-22 sensor, with the following debug code insertion, it reads well.

diff --git a/gpio/dht_sensor/dht.c b/gpio/dht_sensor/dht.c
index 14cb7fa..4178a46 100644
--- a/gpio/dht_sensor/dht.c
+++ b/gpio/dht_sensor/dht.c
@@ -47,6 +47,7 @@ void read_from_dht(dht_reading *result) {
     int data[5] = {0, 0, 0, 0, 0};
     uint last = 1;
     uint j = 0;
+    uint count_seq[85] = {0};
 
     gpio_set_dir(DHT_PIN, GPIO_OUT);
     gpio_put(DHT_PIN, 0);
@@ -65,6 +66,7 @@ void read_from_dht(dht_reading *result) {
             sleep_us(1);
             if (count == 255) break;
         }
+        count_seq[i] = count;
         if (count == 255) break;
         last = !last;
 
@@ -78,6 +80,18 @@ void read_from_dht(dht_reading *result) {
     gpio_put(LED_PIN, 0);
 #endif
 
+    printf("count_seq: ");
+    for (uint i = 0; i < 85; i++) {
+        printf("%d,", count_seq[i]);
+    }
+    printf("\n");
+    printf("j: %d\n", j);
+    printf("data: ");
+    for (uint i = 0; i < 5; i++) {
+        printf("%d,", data[i]);
+    }
+    printf("\n");
+
     if ((j >= 40) && (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF))) {
         result->humidity = (float) ((data[0] << 8) + data[1]) / 10;
         if (result->humidity > 100) {

I recorded the actual loop count, my output is as follows:

count_seq: 32,81,82,53,22,51,22,52,22,51,22,51,22,52,22,51,68,52,24,51,69,51,22,51,22,51,69,51,68,52,22,51,22,51,25,52,22,51,22,51,22,51,22,52,22,51,22,51,22,51,71,52,22,51,22,51,22,51,22,52,68,51,23,51,22,51,25,51,69,51,22,51,68,52,22,51,22,51,22,51,69,51,68,0,0,
j: 40
data: 2,152,1,8,163,
Humidity = 66.4%, Temperature = 26.4C (79.5F)
count_seq: 32,82,81,54,22,51,22,51,22,52,22,51,22,52,22,51,68,52,24,51,69,51,22,52,22,51,69,51,22,52,68,52,68,51,72,51,22,52,22,51,22,51,23,51,22,51,22,52,22,51,71,51,23,51,22,51,22,52,22,51,69,51,22,51,22,52,25,51,69,51,22,51,69,51,22,52,22,51,22,51,69,51,22,0,0,
j: 40
data: 2,151,1,8,162,
Humidity = 66.3%, Temperature = 26.4C (79.5F)
count_seq: 32,81,81,53,22,52,22,51,22,51,22,51,22,51,22,51,69,51,24,51,68,51,22,52,22,51,68,51,69,51,22,51,22,51,25,51,22,51,22,51,22,51,22,51,22,51,22,52,22,51,70,51,22,51,23,51,22,51,22,51,68,51,22,51,22,51,26,51,68,51,22,51,69,51,22,51,22,51,22,51,68,52,68,0,0,
j: 40
data: 2,152,1,8,163,
Humidity = 66.4%, Temperature = 26.4C (79.5F)
count_seq: 32,81,81,53,22,51,22,51,22,52,22,51,22,51,22,51,68,51,24,51,69,51,22,51,22,51,68,51,69,51,22,51,22,51,25,51,22,51,22,51,22,51,22,51,22,51,22,51,22,52,70,51,22,51,22,52,22,51,22,51,68,51,22,51,22,52,25,51,68,51,22,51,69,51,22,51,22,51,22,51,68,51,69,0,0,
j: 40
data: 2,152,1,8,163,
Humidity = 66.4%, Temperature = 26.4C (79.5F)