gattc/*: DeviceCharacteristic Read() implementation

Signed-off-by: deadprogram <ron@hybridgroup.com>

Makefile

@@ -11,6 +11,8 @@ smoketest-tinygo:
 	@md5sum test.hex
 	$(TINYGO) build -o test.uf2 -size=short -target=circuitplay-bluefruit ./examples/circuitplay
 	@md5sum test.hex
+	$(TINYGO) build -o test.uf2 -size=short -target=circuitplay-bluefruit ./examples/discover
+	@md5sum test.hex
 	$(TINYGO) build -o test.hex -size=short -target=pca10040-s132v6       ./examples/heartrate
 	@md5sum test.hex
 	$(TINYGO) build -o test.hex -size=short -target=reelboard-s140v7      ./examples/ledcolor

adapter_nrf528xx.go

@@ -219,6 +219,17 @@ func handleEvent() {
 					}
 				}
 			}
+		case C.BLE_GATTC_EVT_READ_RSP:
+			readEvent := gattcEvent.params.unionfield_read_rsp()
+			if debug {
+				println("evt: read response, data length", readEvent.len)
+			}
+			readingCharacteristic.handle_value.Set(readEvent.handle)
+			readingCharacteristic.offset = readEvent.offset
+			readingCharacteristic.length = readEvent.len
+
+			// copy read event data into Go slice
+			copy(readingCharacteristic.value, (*[255]byte)(unsafe.Pointer(&readEvent.data[0]))[:readEvent.len:readEvent.len])
 		case C.BLE_GATTC_EVT_HVX:
 			hvxEvent := gattcEvent.params.unionfield_hvx()
 			switch hvxEvent._type {

examples/discover/main.go

@@ -17,6 +17,8 @@
 package main
 
 import (
+	"strconv"
+
 	"tinygo.org/x/bluetooth"
 )
 
@@ -59,6 +61,9 @@ func main() {
 	srvcs, err := device.DiscoverServices(nil)
 	must("discover services", err)
 
+	// buffer to retrieve characteristic data
+	buf := make([]byte, 255)
+
 	for _, srvc := range srvcs {
 		println("- service", srvc.UUID().String())
 
@@ -68,6 +73,13 @@ func main() {
 		}
 		for _, char := range chars {
 			println("-- characteristic", char.UUID().String())
+			n, err := char.Read(buf)
+			if err != nil {
+				println("    ", err.Error())
+			} else {
+				println("    data bytes", strconv.Itoa(n))
+				println("    value =", string(buf[:n]))
+			}
 		}
 	}
 

gap_darwin.go

@@ -156,12 +156,17 @@ func (pd *peripheralDelegate) DidDiscoverCharacteristics(prph cbgo.Peripheral, s
 }
 
 // DidUpdateValueForCharacteristic is called when the characteristic for a Service
-// for a Peripheral receives a notification with a new value.
+// for a Peripheral receives a notification with a new value,
+// or receives a value for a read request.
 func (pd *peripheralDelegate) DidUpdateValueForCharacteristic(prph cbgo.Peripheral, chr cbgo.Characteristic, err error) {
 	uuid, _ := ParseUUID(chr.UUID().String())
 	if char, ok := pd.d.characteristics[uuid]; ok {
-		if char != nil && char.callback != nil {
+		if err == nil && char.callback != nil {
 			go char.callback(chr.Value())
 		}
+
+		if char.readChan != nil {
+			char.readChan <- err
+		}
 	}
 }

gattc_darwin.go

@@ -92,9 +92,11 @@ func (s *DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacter
 		for _, dchar := range s.service.Characteristics() {
 			uuid, _ := ParseUUID(dchar.UUID().String())
 			char := DeviceCharacteristic{
-				uuidWrapper:    uuid,
-				service:        s,
-				characteristic: dchar,
+				deviceCharacteristic: &deviceCharacteristic{
+					uuidWrapper:    uuid,
+					service:        s,
+					characteristic: dchar,
+				},
 			}
 			chars = append(chars, char)
 			s.device.characteristics[char.uuidWrapper] = &char
@@ -108,12 +110,17 @@ func (s *DeviceService) DiscoverCharacteristics(uuids []UUID) ([]DeviceCharacter
 // DeviceCharacteristic is a BLE characteristic on a connected peripheral
 // device.
 type DeviceCharacteristic struct {
+	*deviceCharacteristic
+}
+
+type deviceCharacteristic struct {
 	uuidWrapper
 
 	service *DeviceService
 
 	characteristic cbgo.Characteristic
 	callback       func(buf []byte)
+	readChan       chan error
 }
 
 // UUID returns the UUID for this DeviceCharacteristic.
@@ -145,3 +152,24 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 
 	return nil
 }
+
+// Read reads the current characteristic value.
+func (c *deviceCharacteristic) Read(data []byte) (n int, err error) {
+	c.readChan = make(chan error)
+	c.service.device.prph.ReadCharacteristic(c.characteristic)
+
+	// wait for result
+	select {
+	case err := <-c.readChan:
+		c.readChan = nil
+		if err != nil {
+			return 0, err
+		}
+	case <-time.NewTimer(10 * time.Second).C:
+		c.readChan = nil
+		return 0, errors.New("timeout on Read()")
+	}
+
+	copy(data, c.characteristic.Value())
+	return len(c.characteristic.Value()), nil
+}

gattc_linux.go

@@ -231,3 +231,14 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 	}()
 	return c.characteristic.StartNotify()
 }
+
+// Read reads the current characteristic value.
+func (c *DeviceCharacteristic) Read(data []byte) (int, error) {
+	options := make(map[string]interface{})
+	result, err := c.characteristic.ReadValue(options)
+	if err != nil {
+		return 0, err
+	}
+	copy(data, result)
+	return len(result), nil
+}

gattc_sd.go

@@ -414,3 +414,39 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 	})
 	return makeError(errCode)
 }
+
+// A global used to pass information from the event handler back to the
+// Read function below.
+var readingCharacteristic struct {
+	handle_value volatile.Register16
+	offset       uint16
+	length       uint16
+	value        []byte
+}
+
+// Read reads the current characteristic value up to MTU length.
+// A future enhancement would be to be able to retrieve a longer
+// value by making multiple calls.
+func (c *DeviceCharacteristic) Read(data []byte) (n int, err error) {
+	// global will copy bytes from read operation into data slice
+	readingCharacteristic.value = data
+
+	errCode := C.sd_ble_gattc_read(c.connectionHandle, c.valueHandle, 0)
+	if errCode != 0 {
+		return 0, Error(errCode)
+	}
+
+	// wait for response with data
+	for readingCharacteristic.handle_value.Get() == 0 {
+		arm.Asm("wfe")
+	}
+
+	// how much data was read into buffer
+	n = int(readingCharacteristic.length)
+
+	// prepare for next read
+	readingCharacteristic.handle_value.Set(0)
+	readingCharacteristic.length = 0
+
+	return
+}