8000 drivers/dht: Add option to do the measure without blocking interrupts. · micropython/micropython@cca2f91 · GitHub
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EddieParisEddieParis
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drivers/dht: Add option to do the measure without blocking interrupts.
This is done because ESP8266 has a PWM relying on interrupts. Doing the DHT measure with interruption blocking, sometimes makes glitches on the PWM.
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-8
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3 files changed

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-8
lines changed

‎docs/esp8266/tutorial/dht.rst

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -63,3 +63,22 @@ To make newer I2C sensors work in backwards compatible 1-wire mode, you must
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connect both pins 3 and 4 to GND. This disables the I2C interface.
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DHT22 sensors are now sold under the name AM2302 and are otherwise identical.
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NOTE: if your are using a PWM channel in parallel of your measure, there can
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be some glitches on the PWM channel at the measure time. This is because
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the DHT drivers locks interrupts for accurate protocol timing handling,
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and the PWM driver relies on these interrupts. The constructor of the DHT
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objects has an extra argument irq_lock which can be set to False.
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The risk is low, but in case of timing issues a DHTChecksumError can be
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raised, catch it and retry.
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>>> import dht
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>>> import machine
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>>> d = dht.DHT22(machine.Pin(4), False)
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>>> measure_ok = False
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>>> while not measure_ok:
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>>> try:
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>>> d.measure()
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>>> measure_ok = True
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>>> except dht.DHTChecksumError:
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>>> pass

‎drivers/dht/dht.c

Lines changed: 13 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,9 @@
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#define mp_hal_pin_od_high_dht mp_hal_pin_od_high
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#endif
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40-
STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
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STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in, mp_obj_t irq_lock) {
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mp_uint_t irq_state=0;
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mp_hal_pin_obj_t pin = mp_hal_get_pin_obj(pin_in);
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mp_hal_pin_open_drain(pin);
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@@ -54,7 +56,9 @@ STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
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mp_hal_pin_od_low(pin);
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mp_hal_delay_ms(18);
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57-
mp_uint_t irq_state = mp_hal_quiet_timing_enter();
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if (mp_obj_is_true(irq_lock)) {
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irq_state = mp_hal_quiet_timing_enter();
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}
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// release the line so the device can respond
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mp_hal_pin_od_high_dht(pin);
@@ -84,11 +88,15 @@ STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
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buf[i / 8] = (buf[i / 8] << 1) | (ticks > 48);
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}
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mp_hal_quiet_timing_exit(irq_state);
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if (mp_obj_is_true(irq_lock)) {
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mp_hal_quiet_timing_exit(irq_state);
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}
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return mp_const_none;
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timeout:
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mp_hal_quiet_timing_exit(irq_state);
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if (mp_obj_is_true(irq_lock)) {
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mp_hal_quiet_timing_exit(irq_state);
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}
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mp_raise_OSError(MP_ETIMEDOUT);
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}
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MP_DEFINE_CONST_FUN_OBJ_2(dht_readinto_obj, dht_readinto);
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MP_DEFINE_CONST_FUN_OBJ_3(dht_readinto_obj, dht_readinto);

‎drivers/dht/dht.py

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,16 +7,21 @@
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from pyb import dht_readinto
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class DHTChecksumError(Exception):
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pass
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class DHTBase:
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def __init__(self, pin):
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def __init__(self, pin, irq_block=True):
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self.pin = pin
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self.buf = bytearray(5)
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self.irq_block = irq_block
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def measure(self):
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buf = self.buf
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dht_readinto(self.pin, buf)
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dht_readinto(self.pin, buf, self.irq_block)
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if (buf[0] + buf[1] + buf[2] + buf[3]) & 0xFF != buf[4]:
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raise Exception("checksum error")
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raise DHTChecksumError("Measure failed")
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class DHT11(DHTBase):

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