diff --git a/docs/esp8266/tutorial/dht.rst b/docs/esp8266/tutorial/dht.rst
index 1602e8a337455..92e837966b936 100644
--- a/docs/esp8266/tutorial/dht.rst
+++ b/docs/esp8266/tutorial/dht.rst
@@ -63,3 +63,22 @@ To make newer I2C sensors work in backwards compatible 1-wire mode, you must
connect both pins 3 and 4 to GND. This disables the I2C interface.
DHT22 sensors are now sold under the name AM2302 and are otherwise identical.
+
+NOTE: if your are using a PWM channel in parallel of your measure, there can
+be some glitches on the PWM channel at the measure time. This is because
+the DHT drivers locks interrupts for accurate protocol timing handling,
+and the PWM driver relies on these interrupts. The constructor of the DHT
+objects has an extra argument irq_lock which can be set to False.
+The risk is low, but in case of timing issues a DHTChecksumError can be
+raised, catch it and retry. Depending on your use case, consider limiting
+the number of retries.
+
+ >>> import dht
+ >>> import machine
+ >>> d = dht.DHT22(machine.Pin(4), False)
+ >>> while True:
+ >>> try:
+ >>> d.measure()
+ >>> break
+ >>> except dht.DHTChecksumError:
+ >>> pass
diff --git a/drivers/dht/dht.c b/drivers/dht/dht.c
index 81754ac15f43f..4c4061fa298b8 100644
--- a/drivers/dht/dht.c
+++ b/drivers/dht/dht.c
@@ -37,7 +37,11 @@
#define mp_hal_pin_od_high_dht mp_hal_pin_od_high
#endif
-STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
+STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in, mp_obj_t irq_lock) {
+ mp_uint_t irq_state = 0;
+
+ const bool do_lock = mp_obj_is_true(irq_lock);
+
mp_hal_pin_obj_t pin = mp_hal_get_pin_obj(pin_in);
mp_hal_pin_open_drain(pin);
@@ -54,7 +58,9 @@ STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
mp_hal_pin_od_low(pin);
mp_hal_delay_ms(18);
- mp_uint_t irq_state = mp_hal_quiet_timing_enter();
+ if (do_lock) {
+ irq_state = mp_hal_quiet_timing_enter();
+ }
// release the line so the device can respond
mp_hal_pin_od_high_dht(pin);
@@ -84,11 +90,15 @@ STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
buf[i / 8] = (buf[i / 8] << 1) | (ticks > 48);
}
- mp_hal_quiet_timing_exit(irq_state);
+ if (do_lock) {
+ mp_hal_quiet_timing_exit(irq_state);
+ }
return mp_const_none;
timeout:
- mp_hal_quiet_timing_exit(irq_state);
+ if (do_lock) {
+ mp_hal_quiet_timing_exit(irq_state);
+ }
mp_raise_OSError(MP_ETIMEDOUT);
}
-MP_DEFINE_CONST_FUN_OBJ_2(dht_readinto_obj, dht_readinto);
+MP_DEFINE_CONST_FUN_OBJ_3(dht_readinto_obj, dht_readinto);
diff --git a/drivers/dht/dht.py b/drivers/dht/dht.py
index 1163b382bbc77..a86c1927111ff 100644
--- a/drivers/dht/dht.py
+++ b/drivers/dht/dht.py
@@ -7,16 +7,21 @@
from pyb import dht_readinto
+class DHTChecksumError(Exception):
+ pass
+
+
class DHTBase:
- def __init__(self, pin):
+ def __init__(self, pin, irq_block=True):
self.pin = pin
self.buf = bytearray(5)
+ self.irq_block = irq_block
def measure(self):
buf = self.buf
- dht_readinto(self.pin, buf)
+ dht_readinto(self.pin, buf, self.irq_block)
if (buf[0] + buf[1] + buf[2] + buf[3]) & 0xFF != buf[4]:
- raise Exception("checksum error")
+ raise DHTChecksumError("Measure failed")
class DHT11(DHTBase):
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