nrf: PDMIn: Implement

So far, this supports only 16kHz and 16-bit samples with a fixed gain.
This is enough to support the basic functionality of e.g., sensing
ambient audio levels.

ports/nrf/common-hal/audiobusio/PDMIn.c

@@ -25,9 +25,15 @@
  */
 
 #include "common-hal/audiobusio/PDMIn.h"
+#include "shared-bindings/microcontroller/Pin.h"
 
 #include "py/runtime.h"
 
+__attribute__((used))
+NRF_PDM_Type *nrf_pdm = NRF_PDM;
+
+static uint32_t dummy_buffer[4];
+
 void common_hal_audiobusio_pdmin_construct(audiobusio_pdmin_obj_t* self,
                                            const mcu_pin_obj_t* clock_pin,
                                            const mcu_pin_obj_t* data_pin,
@@ -35,30 +41,90 @@ void common_hal_audiobusio_pdmin_construct(audiobusio_pdmin_obj_t* self,
                                            uint8_t bit_depth,
                                            bool mono,
                                            uint8_t oversample) {
-    mp_raise_RuntimeError(translate("not implemented"));
+    assert_pin_free(clock_pin);
+    assert_pin_free(data_pin);
+    claim_pin(clock_pin);
+    claim_pin(data_pin);
+
+    self->mono = mono;
+    self->clock_pin_number = clock_pin->number;
+    self->data_pin_number = data_pin->number;
+
+    if (sample_rate != 16000) {
+        mp_raise_ValueError(translate("only sample_rate=16000 is supported"));
+    }
+    if (bit_depth != 16) {
+        mp_raise_ValueError(translate("only bit_depth=16 is supported"));
+    }
+    nrf_pdm->PSEL.CLK = self->clock_pin_number;
+    nrf_pdm->PSEL.DIN = self->data_pin_number;
+    nrf_pdm->PDMCLKCTRL = PDM_PDMCLKCTRL_FREQ_Default; // For Ratio64
+    nrf_pdm->RATIO = PDM_RATIO_RATIO_Ratio64;
+    nrf_pdm->GAINL = PDM_GAINL_GAINL_DefaultGain;
+    nrf_pdm->GAINR = PDM_GAINR_GAINR_DefaultGain;
+    nrf_pdm->ENABLE = 1;
+
+    nrf_pdm->SAMPLE.PTR = (uintptr_t)&dummy_buffer;
+    nrf_pdm->SAMPLE.MAXCNT = 1;
+    nrf_pdm->TASKS_START = 1;
 }
 
 bool common_hal_audiobusio_pdmin_deinited(audiobusio_pdmin_obj_t* self) {
-    mp_raise_RuntimeError(translate("not implemented"));
+    return !self->clock_pin_number;
 }
 
 void common_hal_audiobusio_pdmin_deinit(audiobusio_pdmin_obj_t* self) {
-    mp_raise_RuntimeError(translate("not implemented"));
+    nrf_pdm->ENABLE = 0;
+
+    reset_pin_number(self->clock_pin_number);
+    self->clock_pin_number = 0;
+    reset_pin_number(self->data_pin_number);
+    self->data_pin_number = 0;
 }
 
 uint8_t common_hal_audiobusio_pdmin_get_bit_depth(audiobusio_pdmin_obj_t* self) {
-    return self->bit_depth;
+    return 16;
 }
 
 uint32_t common_hal_audiobusio_pdmin_get_sample_rate(audiobusio_pdmin_obj_t* self) {
-    return self->sample_rate;
+    return 16000;
 }
 
 uint32_t common_hal_audiobusio_pdmin_record_to_buffer(audiobusio_pdmin_obj_t* self,
         uint16_t* output_buffer, uint32_t output_buffer_length) {
-    mp_raise_RuntimeError(translate("not implemented"));
-}
+    // Note: Adafruit's module has SELECT pulled to GND, which makes the DATA
+    // valid when the CLK is low, therefore it must be sampled on the rising edge.
+    if (self->mono) {
+        nrf_pdm->MODE = PDM_MODE_OPERATION_Stereo | PDM_MODE_EDGE_LeftRising;
+    } else {
+        nrf_pdm->MODE = PDM_MODE_OPERATION_Mono | PDM_MODE_EDGE_LeftRising;
+    }
+
+    // step 1. Redirect to real buffer
+    nrf_pdm->SAMPLE.PTR = (uintptr_t)output_buffer;
+    nrf_pdm->SAMPLE.MAXCNT = output_buffer_length;
+
+    // a delay is the safest simple way to ensure that the above requested sample has started
+    mp_hal_delay_us(200);
+    nrf_pdm->EVENTS_END = 0;
+
+    // step 2. Registers are double buffered, so pre-redirect back to dummy buffer
+    nrf_pdm->SAMPLE.PTR = (uintptr_t)&dummy_buffer;
+    nrf_pdm->SAMPLE.MAXCNT = 1;
+
+    // Step 3. wait for PDM to end
+    while (!nrf_pdm->EVENTS_END) {
+       MICROPY_VM_HOOK_LOOP;
+    }
+
+    // Step 4. They want unsigned
+    for (uint32_t i=0; i<output_buffer_length; i++) {
+        output_buffer[i] += 32768;
+    }
 
-void common_hal_audiobusio_pdmin_record_to_file(audiobusio_pdmin_obj_t* self, uint8_t* buffer, uint32_t length) {
-    mp_raise_RuntimeError(translate("not implemented"));
+    if (self->mono) {
+        return (output_buffer_length / 2) * 2;
+    } else {
+        return (output_buffer_length / 4) * 4;
+    }
 }

ports/nrf/common-hal/audiobusio/PDMIn.h

@@ -33,11 +33,8 @@
 
 typedef struct {
     mp_obj_base_t base;
-    const mcu_pin_obj_t *clock_pin;
-    const mcu_pin_obj_t *data_pin;
-    uint32_t sample_rate;
-    uint8_t bytes_per_sample;
-    uint8_t bit_depth;
+    uint8_t clock_pin_number, data_pin_number;
+    bool mono;
 } audiobusio_pdmin_obj_t;
 
 #endif