drivers: Add C-level function to read DHT11 and DHT22 devices.

Uses mp_hal_pin API.

drivers/dht/dht.c

+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "py/runtime.h"
+#include "py/mperrno.h"
+#include "py/mphal.h"
+#include "drivers/dht/dht.h"
+
+STATIC mp_uint_t time_pulse_us(mp_hal_pin_obj_t pin, int pulse_value, mp_uint_t timeout) {
+    mp_uint_t start = mp_hal_ticks_us();
+    while (mp_hal_pin_read(pin) != pulse_value) {
+        if ((mp_uint_t)(mp_hal_ticks_us() - start) >= timeout) {
+            return (mp_uint_t)-1;
+        }
+    }
+    start = mp_hal_ticks_us();
+    while (mp_hal_pin_read(pin) == pulse_value) {
+        if ((mp_uint_t)(mp_hal_ticks_us() - start) >= timeout) {
+            return (mp_uint_t)-1;
+        }
+    }
+    return mp_hal_ticks_us() - start;
+}
+
+STATIC mp_obj_t dht_readinto(mp_obj_t pin_in, mp_obj_t buf_in) {
+    mp_hal_pin_obj_t pin = mp_hal_get_pin_obj(pin_in);
+    mp_hal_pin_open_drain(pin);
+
+    mp_buffer_info_t bufinfo;
+    mp_get_buffer_raise(buf_in, &bufinfo, MP_BUFFER_WRITE);
+
+    if (bufinfo.len < 5) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "buffer too small"));
+    }
+
+    // issue start command
+    mp_hal_pin_od_high(pin);
+    mp_hal_delay_ms(250);
+    mp_hal_pin_od_low(pin);
+    mp_hal_delay_ms(18);
+
+    mp_uint_t irq_state = mp_hal_quiet_timing_enter();
+
+    // release the line so the device can respond
+    mp_hal_pin_od_high(pin);
+    mp_hal_delay_us_fast(10);
+
+    // wait for device to respond
+    mp_uint_t ticks = mp_hal_ticks_us();
+    while (mp_hal_pin_read(pin) != 0) {
+        if ((mp_uint_t)(mp_hal_ticks_us() - ticks) > 100) {
+            goto timeout;
+        }
+    }
+
+    // time pulse, should be 80us
+    ticks = time_pulse_us(pin, 1, 150);
+    if (ticks == (mp_uint_t)-1) {
+        goto timeout;
+    }
+
+    // time 40 pulses for data (either 26us or 70us)
+    uint8_t *buf = bufinfo.buf;
+    for (int i = 0; i < 40; ++i) {
+        ticks = time_pulse_us(pin, 1, 100);
+        if (ticks == (mp_uint_t)-1) {
+            goto timeout;
+        }
+        buf[i / 8] = (buf[i / 8] << 1) | (ticks > 48);
+    }
+
+    mp_hal_quiet_timing_exit(irq_state);
+    return mp_const_none;
+
+timeout:
+    mp_hal_quiet_timing_exit(irq_state);
+    nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(MP_ETIMEDOUT)));
+}
+MP_DEFINE_CONST_FUN_OBJ_2(dht_readinto_obj, dht_readinto);

drivers/dht/dht.h

+#include "py/obj.h"
+
+MP_DECLARE_CONST_FUN_OBJ(dht_readinto_obj);