From e7ba07dd5ad1760feaf392e788c0754bdc1a9e8c Mon Sep 17 00:00:00 2001
From: Marcus Sorensen <shadowsor@gmail.com>
Date: Tue, 17 Jan 2023 04:32:01 -0700
Subject: [PATCH] Add PDM support for circuitplay-bluefruit (#3359)

machine/nrf52840: add PDM support

Signed-off-by: Marcus Sorensen <marcus@turboio.com>
---
 src/examples/pdm/pdm.go                    | 27 +++++++++
 src/machine/board_circuitplay_bluefruit.go |  6 ++
 src/machine/machine_nrf52840.go            | 70 ++++++++++++++++++++++
 src/machine/pdm.go                         |  7 +++
 4 files changed, 110 insertions(+)
 create mode 100644 src/examples/pdm/pdm.go
 create mode 100644 src/machine/pdm.go

diff --git a/src/examples/pdm/pdm.go b/src/examples/pdm/pdm.go
new file mode 100644
index 00000000..c48a0a17
--- /dev/null
+++ b/src/examples/pdm/pdm.go
@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"machine"
+)
+
+var (
+	audio = make([]int16, 16)
+	pdm   = machine.PDM{}
+)
+
+func main() {
+	machine.BUTTONA.Configure(machine.PinConfig{Mode: machine.PinInputPulldown})
+	err := pdm.Configure(machine.PDMConfig{CLK: machine.PDM_CLK_PIN, DIN: machine.PDM_DIN_PIN})
+	if err != nil {
+		panic(fmt.Sprintf("Failed to configure PDM:%v", err))
+	}
+
+	for {
+		if machine.BUTTONA.Get() {
+			println("Recording new audio clip into memory")
+			pdm.Read(audio)
+			println(fmt.Sprintf("Recorded new audio clip into memory: %v", audio))
+		}
+	}
+}
diff --git a/src/machine/board_circuitplay_bluefruit.go b/src/machine/board_circuitplay_bluefruit.go
index d578760b..a133003c 100644
--- a/src/machine/board_circuitplay_bluefruit.go
+++ b/src/machine/board_circuitplay_bluefruit.go
@@ -73,6 +73,12 @@ const (
 	SPI0_SDI_PIN = P0_23 // SDI
 )
 
+// PDM pins
+const (
+	PDM_CLK_PIN = P0_17 // CLK
+	PDM_DIN_PIN = P0_16 // DIN
+)
+
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Adafruit Circuit Playground Bluefruit"
diff --git a/src/machine/machine_nrf52840.go b/src/machine/machine_nrf52840.go
index 005bf252..d38ebbe5 100644
--- a/src/machine/machine_nrf52840.go
+++ b/src/machine/machine_nrf52840.go
@@ -4,6 +4,8 @@ package machine
 
 import (
 	"device/nrf"
+	"errors"
+	"unsafe"
 )
 
 // Get peripheral and pin number for this GPIO pin.
@@ -32,3 +34,71 @@ var (
 	PWM2 = &PWM{PWM: nrf.PWM2}
 	PWM3 = &PWM{PWM: nrf.PWM3}
 )
+
+// PDM represents a PDM device
+type PDM struct {
+	device        *nrf.PDM_Type
+	defaultBuffer int16
+}
+
+// Configure is intended to set up the PDM interface prior to use.
+func (pdm *PDM) Configure(config PDMConfig) error {
+	if config.DIN == 0 {
+		return errors.New("No DIN pin provided in configuration")
+	}
+
+	if config.CLK == 0 {
+		return errors.New("No CLK pin provided in configuration")
+	}
+
+	config.DIN.Configure(PinConfig{Mode: PinInput})
+	config.CLK.Configure(PinConfig{Mode: PinOutput})
+	pdm.device = nrf.PDM
+	pdm.device.PSEL.DIN.Set(uint32(config.DIN))
+	pdm.device.PSEL.CLK.Set(uint32(config.CLK))
+	pdm.device.PDMCLKCTRL.Set(nrf.PDM_PDMCLKCTRL_FREQ_Default)
+	pdm.device.RATIO.Set(nrf.PDM_RATIO_RATIO_Ratio64)
+	pdm.device.GAINL.Set(nrf.PDM_GAINL_GAINL_DefaultGain)
+	pdm.device.GAINR.Set(nrf.PDM_GAINR_GAINR_DefaultGain)
+	pdm.device.ENABLE.Set(nrf.PDM_ENABLE_ENABLE_Enabled)
+
+	if config.Stereo {
+		pdm.device.MODE.Set(nrf.PDM_MODE_OPERATION_Stereo | nrf.PDM_MODE_EDGE_LeftRising)
+	} else {
+		pdm.device.MODE.Set(nrf.PDM_MODE_OPERATION_Mono | nrf.PDM_MODE_EDGE_LeftRising)
+	}
+
+	pdm.device.SAMPLE.SetPTR(uint32(uintptr(unsafe.Pointer(&pdm.defaultBuffer))))
+	pdm.device.SAMPLE.SetMAXCNT_BUFFSIZE(1)
+	pdm.device.SetTASKS_START(1)
+	return nil
+}
+
+// Read stores a set of samples in the given target buffer.
+func (pdm *PDM) Read(buf []int16) (uint32, error) {
+	pdm.device.SAMPLE.SetPTR(uint32(uintptr(unsafe.Pointer(&buf[0]))))
+	pdm.device.SAMPLE.MAXCNT.Set(uint32(len(buf)))
+	pdm.device.EVENTS_STARTED.Set(0)
+
+	// Step 1: wait for new sampling to start for target buffer
+	for !pdm.device.EVENTS_STARTED.HasBits(nrf.PDM_EVENTS_STARTED_EVENTS_STARTED) {
+	}
+	pdm.device.EVENTS_END.Set(0)
+
+	// Step 2: swap out buffers for next recording so we don't continue to
+	// write to the target buffer
+	pdm.device.EVENTS_STARTED.Set(0)
+	pdm.device.SAMPLE.SetPTR(uint32(uintptr(unsafe.Pointer(&pdm.defaultBuffer))))
+	pdm.device.SAMPLE.MAXCNT.Set(1)
+
+	// Step 3: wait for original event to end
+	for pdm.device.EVENTS_END.HasBits(nrf.PDM_EVENTS_STOPPED_EVENTS_STOPPED) {
+	}
+
+	// Step 4: wait for default buffer to start recording before proceeding
+	// otherwise we see the contents of target buffer change later
+	for !pdm.device.EVENTS_STARTED.HasBits(nrf.PDM_EVENTS_STARTED_EVENTS_STARTED) {
+	}
+
+	return uint32(len(buf)), nil
+}
diff --git a/src/machine/pdm.go b/src/machine/pdm.go
new file mode 100644
index 00000000..e57ad0f6
--- /dev/null
+++ b/src/machine/pdm.go
@@ -0,0 +1,7 @@
+package machine
+
+type PDMConfig struct {
+	Stereo bool
+	DIN    Pin
+	CLK    Pin
+}