all: add SetConnectionLatency to update connection parameters

This allows changing the connection latency, slave latency, and
connection timeout of an active connection - whether in the central or
peripheral role. This is especially helpful on battery operated BLE
devices that don't have a lot of power and need to lower the connection
latency for improved speed. It might also be useful for devices that
need high speed, as the defaults might be too low.

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.hex -size=short -target=circuitplay-bluefruit ./examples/connparams
+	@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
@@ -40,6 +42,7 @@ smoketest-tinygo:
 smoketest-linux:
 	# Test on Linux.
 	GOOS=linux go build -o /tmp/go-build-discard ./examples/advertisement
+	GOOS=linux go build -o /tmp/go-build-discard ./examples/connparams
 	GOOS=linux go build -o /tmp/go-build-discard ./examples/heartrate
 	GOOS=linux go build -o /tmp/go-build-discard ./examples/heartrate-monitor
 	GOOS=linux go build -o /tmp/go-build-discard ./examples/nusserver

examples/connparams/main.go

@@ -0,0 +1,84 @@
+// Test for setting connection parameters.
+//
+// To test this feature, run this either on a desktop OS or by flashing it to a
+// device with TinyGo. Then connect to it from a BLE connection debugger, for
+// example nRF Connect on Android. After a second, you should see in the log of
+// the BLE app that the connection latency has been updated. It might look
+// something like this:
+//
+//	Connection parameters updated (interval: 510.0ms, latency: 0, timeout: 10000ms)
+package main
+
+import (
+	"time"
+
+	"tinygo.org/x/bluetooth"
+)
+
+var (
+	adapter   = bluetooth.DefaultAdapter
+	newDevice chan bluetooth.Device
+)
+
+func main() {
+	must("enable BLE stack", adapter.Enable())
+
+	newDevice = make(chan bluetooth.Device, 1)
+	adapter.SetConnectHandler(func(device bluetooth.Device, connected bool) {
+		// If this is a new device, signal it to the separate goroutine.
+		if connected {
+			select {
+			case newDevice <- device:
+			default:
+			}
+		}
+	})
+
+	// Start advertising, so we can be found.
+	const name = "Go BLE test"
+	adv := adapter.DefaultAdvertisement()
+	adv.Configure(bluetooth.AdvertisementOptions{
+		LocalName: name,
+	})
+	adv.Start()
+	println("advertising:", name)
+
+	for device := range newDevice {
+		println("connection from device:", device.Address.String())
+
+		// Discover services and characteristics.
+		svcs, err := device.DiscoverServices(nil)
+		if err != nil {
+			println("  failed to resolve services:", err)
+		}
+		for _, svc := range svcs {
+			println("  service:", svc.UUID().String())
+			chars, err := svc.DiscoverCharacteristics(nil)
+			if err != nil {
+				println("    failed to resolve characteristics:", err)
+			}
+			for _, char := range chars {
+				println("    characteristic:", char.UUID().String())
+			}
+		}
+
+		// Update connection parameters (as a test).
+		time.Sleep(time.Second)
+		err = device.SetConnectionLatency(bluetooth.ConnectionLatency{
+			MinInterval: bluetooth.NewDuration(495 * time.Millisecond),
+			MaxInterval: bluetooth.NewDuration(510 * time.Millisecond),
+			Timeout:     bluetooth.NewDuration(10 * time.Second),
+		})
+		if err != nil {
+			println("  failed to update connection parameters:", err)
+			continue
+		}
+		println("  updated connection parameters")
+	}
+}
+
+func must(action string, err error) {
+	if err != nil {
+		panic("failed to " + action + ": " + err.Error())
+	}
+}

gap.go

@@ -404,3 +404,16 @@ type ConnectionParams struct {
 	MinInterval Duration
 	MaxInterval Duration
 }
+
+// Connection latency and timeout for a connection to a peripheral or central.
+type ConnectionLatency struct {
+	// Connection Supervision Timeout. After this time has passed with no
+	// communication, the connection is considered lost. If no timeout is
+	// specified, the timeout will be unchanged.
+	Timeout Duration
+
+	// Minimum and maximum connection interval to be used for this connection.
+	// Fields that are unset will be unchanged.
+	MinInterval Duration
+	MaxInterval Duration
+}

gap_linux.go

@@ -365,3 +365,14 @@ func (d Device) Disconnect() error {
 	// property change in `watchForConnect` and cancel things then
 	return d.device.Call("org.bluez.Device1.Disconnect", 0).Err
 }
+
+// SetConnectionLatency requests a different connection latency and timeout of
+// the given device connection. Fields that are unset will be left alone.
+// Whether or not the device will actually honor this, depends on the device and
+// on the specific parameters.
+//
+// On Linux, this call doesn't do anything because BlueZ doesn't support
+// changing the connection latency.
+func (d Device) SetConnectionLatency(latency ConnectionLatency) error {
+	return nil
+}

gap_nrf528xx-central.go

@@ -188,3 +188,34 @@ func (d Device) Disconnect() error {
 
 	return nil
 }
+
+// SetConnectionLatency requests a different connection latency and timeout of
+// the given device connection. Fields that are unset will be left alone.
+// Whether or not the device will actually honor this, depends on the device and
+// on the specific parameters.
+//
+// On the Nordic SoftDevice, this call will also set the slave latency to 0.
+func (d Device) SetConnectionLatency(latency ConnectionLatency) error {
+	// The default parameters if no specific parameters are picked.
+	connParams := C.ble_gap_conn_params_t{
+		min_conn_interval: C.BLE_GAP_CP_MIN_CONN_INTVL_NONE,
+		max_conn_interval: C.BLE_GAP_CP_MAX_CONN_INTVL_NONE,
+		slave_latency:     0,
+		conn_sup_timeout:  C.BLE_GAP_CP_CONN_SUP_TIMEOUT_NONE,
+	}
+
+	// Use specified parameters if available.
+	if latency.MinInterval != 0 {
+		connParams.min_conn_interval = C.uint16_t(latency.MinInterval) / 2
+	}
+	if latency.MaxInterval != 0 {
+		connParams.max_conn_interval = C.uint16_t(latency.MaxInterval) / 2
+	}
+	if latency.Timeout != 0 {
+		connParams.conn_sup_timeout = C.uint16_t(latency.Timeout) / 16
+	}
+
+	// Send them to peer device.
+	errCode := C.sd_ble_gap_conn_param_update(d.connectionHandle, &connParams)
+	return makeError(errCode)
+}

gap_windows.go

@@ -247,3 +247,15 @@ func (d Device) Disconnect() error {
 
 	return nil
 }
+
+// SetConnectionLatency requests a different connection latency and timeout of
+// the given device connection. Fields that are unset will be left alone.
+// Whether or not the device will actually honor this, depends on the device and
+// on the specific parameters.
+//
+// On Windows, this call doesn't do anything.
+func (d Device) SetConnectionLatency(latency ConnectionLatency) error {
+	// TODO: implement this using
+	// BluetoothLEDevice.RequestPreferredConnectionParameters.
+	return nil
+}