sd: MTU exchange

adapter_nrf528xx-full.go

@@ -42,6 +42,7 @@ func handleEvent() {
 				}
 				connectionAttempt.connectionHandle = gapEvent.conn_handle
 				connectionAttempt.state.Set(2) // connection was successful
+				mtuExchangeAttempt.state.Set(0)
 				DefaultAdapter.connectHandler(device, true)
 			}
 		case C.BLE_GAP_EVT_DISCONNECTED:
@@ -63,7 +64,7 @@ func handleEvent() {
 				// because it would need to be reconfigured as a non-connectable
 				// advertisement. That's left as a future addition, if
 				// necessary.
-				C.sd_ble_gap_adv_start(defaultAdvertisement.handle, C.BLE_CONN_CFG_TAG_DEFAULT)
+				C.sd_ble_gap_adv_start(defaultAdvertisement.handle, connCfgTag)
 			}
 			device := Device{
 				connectionHandle: gapEvent.conn_handle,
@@ -157,9 +158,16 @@ func handleEvent() {
 			// way to handle it, ignore it.
 			C.sd_ble_gatts_sys_attr_set(gattsEvent.conn_handle, nil, 0, 0)
 		case C.BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST:
-			// This event is generated by some devices. While we could support
-			// larger MTUs, this default MTU is supported everywhere.
-			C.sd_ble_gatts_exchange_mtu_reply(gattsEvent.conn_handle, C.BLE_GATT_ATT_MTU_DEFAULT)
+			rsp := gattsEvent.params.unionfield_exchange_mtu_request()
+			effectiveMtu := min(DefaultAdapter.cfg.Gatt.AttMtu, uint16(rsp.client_rx_mtu))
+			if debug {
+				println("mtu exchange requested. self:", DefaultAdapter.cfg.Gatt.AttMtu, ", peer:", rsp.client_rx_mtu, ", effective:", effectiveMtu)
+			}
+
+			var errCode = C.sd_ble_gatts_exchange_mtu_reply(gattsEvent.conn_handle, C.uint16_t(effectiveMtu))
+			if debug {
+				println("mtu exchange replied, err:", Error(errCode).Error())
+			}
 		case C.BLE_GATTS_EVT_HVN_TX_COMPLETE:
 			// ignore confirmation of a notification successfully sent
 		default:
@@ -255,6 +263,36 @@ func handleEvent() {
 					}
 				}
 			}
+		case C.BLE_GATTC_EVT_EXCHANGE_MTU_RSP:
+			rsp := gattcEvent.params.unionfield_exchange_mtu_rsp()
+			if debug {
+				println("mtu exchanged, effective mtu:", rsp.server_rx_mtu)
+			}
+
+			mtuExchangeAttempt.effectiveMtu = uint16(rsp.server_rx_mtu)
+			mtuExchangeAttempt.state.Set(2) // mtu exchange was successful
+
+			if debug {
+				rsp := gattcEvent.params.unionfield_exchange_mtu_rsp()
+				println("mtu exchanged, effective mtu:", rsp.server_rx_mtu)
+			}
+		case C.BLE_GATTC_EVT_TIMEOUT:
+			timeoutEvt := gattcEvent.params.unionfield_timeout()
+			switch timeoutEvt.src {
+			case C.BLE_GATT_TIMEOUT_SRC_PROTOCOL:
+				// Failed to connect to a peripheral.
+				if debug {
+					println("gattc timeout: src protocol")
+				}
+				mtuExchangeAttempt.state.Set(3) // mtu exchange timed out
+			default:
+				// For example a scan timeout.
+				if debug {
+					println("gattc timeout: other")
+				}
+			}
+		case C.BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE:
+			// no op
 		default:
 			if debug {
 				println("unknown GATTC event:", id, id-C.BLE_GATTC_EVT_BASE)
@@ -266,3 +304,10 @@ func handleEvent() {
 		}
 	}
 }
+
+func min(a, b uint16) uint16 {
+	if a < b {
+		return a
+	}
+	return b
+}

adapter_nrf528xx-peripheral.go

@@ -47,7 +47,7 @@ func handleEvent() {
 				// because it would need to be reconfigured as a non-connectable
 				// advertisement. That's left as a future addition, if
 				// necessary.
-				C.sd_ble_gap_adv_start(defaultAdvertisement.handle, C.BLE_CONN_CFG_TAG_DEFAULT)
+				C.sd_ble_gap_adv_start(defaultAdvertisement.handle, connCfgTag)
 			}
 			device := Device{
 				connectionHandle: gapEvent.conn_handle,
@@ -91,9 +91,16 @@ func handleEvent() {
 			// way to handle it, ignore it.
 			C.sd_ble_gatts_sys_attr_set(gattsEvent.conn_handle, nil, 0, 0)
 		case C.BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST:
-			// This event is generated by some devices. While we could support
-			// larger MTUs, this default MTU is supported everywhere.
-			C.sd_ble_gatts_exchange_mtu_reply(gattsEvent.conn_handle, C.BLE_GATT_ATT_MTU_DEFAULT)
+			rsp := gattsEvent.params.unionfield_exchange_mtu_request()
+			effectiveMtu := min(DefaultAdapter.cfg.Gatt.AttMtu, uint16(rsp.client_rx_mtu))
+			if debug {
+				println("mtu exchange requested. self:", DefaultAdapter.cfg.Gatt.AttMtu, ", peer:", rsp.client_rx_mtu, ", effective:", effectiveMtu)
+			}
+
+			var errCode = C.sd_ble_gatts_exchange_mtu_reply(gattsEvent.conn_handle, C.uint16_t(effectiveMtu))
+			if debug {
+				println("mtu exchange replied, err:", Error(errCode).Error())
+			}
 		case C.BLE_GATTS_EVT_HVN_TX_COMPLETE:
 			// ignore confirmation of a notification successfully sent
 		default:
@@ -107,3 +114,10 @@ func handleEvent() {
 		}
 	}
 }
+
+func min(a, b uint16) uint16 {
+	if a < b {
+		return a
+	}
+	return b
+}

adapter_nrf528xx.go

@@ -31,6 +31,8 @@ var clockConfigXtal C.nrf_clock_lf_cfg_t = C.nrf_clock_lf_cfg_t{
 	accuracy:     C.NRF_CLOCK_LF_ACCURACY_250_PPM,
 }
 
+const connCfgTag uint8 = 1
+
 //go:extern __app_ram_base
 var appRAMBase [0]uint32
 
@@ -47,6 +49,37 @@ func (a *Adapter) enable() error {
 
 	// Enable the BLE stack.
 	appRAMBase := C.uint32_t(uintptr(unsafe.Pointer(&appRAMBase)))
+
+	bleCfg := C.ble_cfg_t{}
+
+	connCfg := bleCfg.unionfield_conn_cfg()
+	connCfg.conn_cfg_tag = connCfgTag
+
+	if a.cfg.Gap.EventLength == 0 {
+		a.cfg.Gap.EventLength = 2
+	}
+
+	gapCfg := connCfg.params.unionfield_gap_conn_cfg()
+	gapCfg.conn_count = 1
+	gapCfg.event_length = a.cfg.Gap.EventLength
+
+	errCode = C.sd_ble_cfg_set(C.uint32_t(C.BLE_CONN_CFG_GAP), &bleCfg, appRAMBase)
+	if errCode != 0 {
+		return Error(errCode)
+	}
+
+	if a.cfg.Gatt.AttMtu == 0 {
+		a.cfg.Gatt.AttMtu = 23
+	}
+
+	gattCfg := connCfg.params.unionfield_gatt_conn_cfg()
+	gattCfg.att_mtu = a.cfg.Gatt.AttMtu
+
+	errCode = C.sd_ble_cfg_set(C.uint32_t(C.BLE_CONN_CFG_GATT), &bleCfg, appRAMBase)
+	if errCode != 0 {
+		return Error(errCode)
+	}
+
 	errCode = C.sd_ble_enable(&appRAMBase)
 	return makeError(errCode)
 }

adapter_sd.go

@@ -33,7 +33,7 @@ var currentConnection = volatileHandle{handle: volatile.Register16{C.BLE_CONN_HA
 // Globally allocated buffer for incoming SoftDevice events.
 var eventBuf struct {
 	C.ble_evt_t
-	buf [23]byte
+	buf [244]byte
 }
 
 func init() {
@@ -49,6 +49,8 @@ type Adapter struct {
 	charWriteHandlers []charWriteHandler
 
 	connectHandler func(device Device, connected bool)
+
+	cfg Config
 }
 
 // DefaultAdapter is the default adapter on the current system. On Nordic chips,
@@ -62,6 +64,42 @@ var DefaultAdapter = &Adapter{isDefault: true,
 
 var eventBufLen C.uint16_t
 
+// Config represents the settings that will be configured to the connection
+// '1' of the SoftDevice.
+type Config struct {
+	Gap  GapConfig
+	Gatt GattConfig
+}
+
+type GapConfig struct {
+	// EventLength is the time set aside for this connection on every
+	// connection interval in 1.25 ms units. The minimum value is 2.
+	EventLength uint16
+}
+
+type GattConfig struct {
+	// AttMtu is the maximum size of ATT packet the SoftDevice can send or
+	// receive. The default and minimum value is 23. The maximum value is 247.
+	// Using ATT_MTU sizes that are multiples of 23 is ideal.
+	AttMtu uint16
+}
+
+// Configure sets the configuration for this adapter.
+// The configuration will be applied when the adapter is enabled.
+func (a *Adapter) Configure(cfg Config) error {
+	if cfg.Gap.EventLength != 0 && cfg.Gap.EventLength < 2 {
+		return errors.New("invalid event length")
+	}
+
+	if cfg.Gatt.AttMtu != 0 && (cfg.Gatt.AttMtu < 23 || cfg.Gatt.AttMtu > 247) {
+		return errors.New("invalid ATT MTU")
+	}
+
+	a.cfg = cfg
+
+	return nil
+}
+
 // Enable configures the BLE stack. It must be called before any
 // Bluetooth-related calls (unless otherwise indicated).
 func (a *Adapter) Enable() error {

gap_nrf528xx-advertisement.go

@@ -74,7 +74,7 @@ func (a *Advertisement) Configure(options AdvertisementOptions) error {
 // Start advertisement. May only be called after it has been configured.
 func (a *Advertisement) Start() error {
 	a.isAdvertising.Set(1)
-	errCode := C.sd_ble_gap_adv_start(a.handle, C.BLE_CONN_CFG_TAG_DEFAULT)
+	errCode := C.sd_ble_gap_adv_start(a.handle, connCfgTag)
 	return makeError(errCode)
 }
 

gap_nrf528xx-central.go

@@ -12,6 +12,7 @@ import (
 
 /*
 #include "ble_gap.h"
+#include "ble_gattc.h"
 */
 import "C"
 
@@ -99,6 +100,11 @@ var connectionAttempt struct {
 	connectionHandle C.uint16_t
 }
 
+var mtuExchangeAttempt struct {
+	state        volatile.Register8 // 0 means unused, 1 means in progress, 2 means exchanged, 3 means timeout
+	effectiveMtu uint16
+}
+
 // Connect starts a connection attempt to the given peripheral device address.
 //
 // Limitations on Nordic SoftDevices inclue that you cannot do more than one
@@ -162,7 +168,7 @@ func (a *Adapter) Connect(address Address, params ConnectionParams) (Device, err
 	connectionAttempt.state.Set(1)
 
 	// Start the connection attempt. We'll get a signal in the event handler.
-	errCode := C.sd_ble_gap_connect(&addr, &scanParams, &connectionParams, C.BLE_CONN_CFG_TAG_DEFAULT)
+	errCode := C.sd_ble_gap_connect(&addr, &scanParams, &connectionParams, connCfgTag)
 	if errCode != 0 {
 		connectionAttempt.state.Set(0)
 		return Device{}, Error(errCode)
@@ -175,6 +181,7 @@ func (a *Adapter) Connect(address Address, params ConnectionParams) (Device, err
 			// Successfully connected.
 			connectionAttempt.state.Set(0)
 			connectionHandle := connectionAttempt.connectionHandle
+
 			return Device{
 				connectionHandle: connectionHandle,
 			}, nil
@@ -190,6 +197,41 @@ func (a *Adapter) Connect(address Address, params ConnectionParams) (Device, err
 	}
 }
 
+// ExchangeMTU starts an MTU exchange request procedure. The effective MTU
+// (the maximum value supported by both parties) is returned.
+func (d Device) ExchangeMTU(mtu uint16) (uint16, error) {
+	if mtuExchangeAttempt.state.Get() == 2 {
+		return 0, errors.New("mtu already exchanged")
+	}
+
+	if mtuExchangeAttempt.state.Get() == 1 {
+		return 0, errors.New("mtu exchange in progress")
+	}
+
+	mtuExchangeAttempt.state.Set(1)
+
+	errCode := C.sd_ble_gattc_exchange_mtu_request(d.connectionHandle, C.uint16_t(mtu))
+	if errCode != 0 {
+		mtuExchangeAttempt.state.Set(0)
+		return 0, Error(errCode)
+	}
+
+	for {
+		state := mtuExchangeAttempt.state.Get()
+		if state == 2 {
+			return mtuExchangeAttempt.effectiveMtu, nil
+		} else if state == 3 {
+			// Timeout while exchanging mtu
+			mtuExchangeAttempt.state.Set(0)
+			return 0, errors.New("mtu exchange timeout")
+		} else {
+			// TODO: use some sort of condition variable once the scheduler
+			// supports them.
+			arm.Asm("wfe")
+		}
+	}
+}
+
 // Disconnect from the BLE device.
 func (d Device) Disconnect() error {
 	errCode := C.sd_ble_gap_disconnect(d.connectionHandle, C.BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION)

gatts_sd.go

@@ -63,7 +63,7 @@ func (a *Adapter) AddService(service *Service) error {
 			},
 			init_len:  C.uint16_t(len(char.Value)),
 			init_offs: 0,
-			max_len:   20, // This is a conservative maximum length.
+			max_len:   C.BLE_GATTS_FIX_ATTR_LEN_MAX,
 		}
 		if len(char.Value) != 0 {
 			value.p_value = (*C.uint8_t)(unsafe.Pointer(&char.Value[0]))