diff --git a/src/actions/ble.ts b/src/actions/ble.ts
index fe9e63e1..c6d2f182 100644
--- a/src/actions/ble.ts
+++ b/src/actions/ble.ts
@@ -2,23 +2,6 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { Action } from 'redux';
-import { ThunkAction } from 'redux-thunk';
-import {
-    PolyfillBluetoothRemoteGATTCharacteristic,
-    polyfillBluetoothRemoteGATTCharacteristic,
-} from '../utils/web-bluetooth';
-import * as notification from './notification';
-
-const pybricksServiceUUID = 'c5f50001-8280-46da-89f4-6d8051e4aeef';
-
-// nRF UART service (Nus)
-const bleNusServiceUUID = '6e400001-b5a3-f393-e0a9-e50e24dcca9e';
-const bleNusCharRXUUID = '6e400002-b5a3-f393-e0a9-e50e24dcca9e';
-const bleNusCharTXUUID = '6e400003-b5a3-f393-e0a9-e50e24dcca9e';
-const bleNusMaxSize = 20;
-
-let device: BluetoothDevice | undefined;
-let rxChar: PolyfillBluetoothRemoteGATTCharacteristic | undefined;
 
 /**
  * Bluetooth low energy connection action types.
@@ -27,7 +10,7 @@ export enum BLEConnectActionType {
     /**
      * Connecting to a device has been requested.
      */
-    WillConnect = 'ble.action.will.connect',
+    Connect = 'ble.action.connect',
     /**
      * The connection completed successfully.
      */
@@ -35,7 +18,7 @@ export enum BLEConnectActionType {
     /**
      * Disconnecting from a device has been requested.
      */
-    WillDisconnect = 'ble.action.will.disconnect',
+    Disconnect = 'ble.action.disconnect',
     /**
      * End async disconnect (can be sent without sending BeginDisconnect first).
      */
@@ -45,141 +28,78 @@ export enum BLEConnectActionType {
 /**
  * Common type for all BLE connection actions.
  */
-type BLEConnectAction = Action<BLEConnectActionType>;
+export type BLEConnectAction = Action<BLEConnectActionType>;
 
 /**
  * Creates an action that indicates connecting has been requested.
  */
-function willConnect(): BLEConnectAction {
-    return { type: BLEConnectActionType.WillConnect };
+export function connect(): BLEConnectAction {
+    return { type: BLEConnectActionType.Connect };
 }
 
 /**
  * Creates an action that indicates a device was connected.
  */
-function didConnect(): BLEConnectAction {
+export function didConnect(): BLEConnectAction {
     return { type: BLEConnectActionType.DidConnect };
 }
 
 /**
  * Creates an action that indicates disconnecting was requested.
  */
-function willDisconnect(): BLEConnectAction {
-    return { type: BLEConnectActionType.WillDisconnect };
+export function disconnect(): BLEConnectAction {
+    return { type: BLEConnectActionType.Disconnect };
 }
 
 /**
  * Creates an action that indicates a device was disconnected.
  */
-function didDisconnect(): BLEConnectAction {
+export function didDisconnect(): BLEConnectAction {
     return { type: BLEConnectActionType.DidDisconnect };
 }
 
 export enum BLEDataActionType {
     /**
-     * Send data.
+     * Write data.
      */
-    SendData = 'ble.data.send',
+    Write = 'ble.data.write',
     /**
-     * Data was received.
+     * Notify that data was received.
      */
-    ReceivedData = 'ble.data.receive',
+    Notify = 'ble.data.receive',
 }
 
-export interface BLEDataAction extends Action<BLEDataActionType> {
+export interface BLEDataWriteAction extends Action<BLEDataActionType.Write> {
+    value: Uint8Array;
+}
+
+export function write(value: Uint8Array): BLEDataWriteAction {
+    return { type: BLEDataActionType.Write, value };
+}
+
+export interface BLEDataNotifyAction extends Action<BLEDataActionType.Notify> {
     value: DataView;
 }
 
-export type BLEThunkAction = ThunkAction<Promise<void>, {}, {}, Action>;
-
-export function connect(): BLEThunkAction {
-    return async function (dispatch): Promise<void> {
-        if (device !== undefined) {
-            dispatch(notification.add('error', 'A device is already connected.'));
-            return;
-        }
-        if (navigator.bluetooth === undefined) {
-            dispatch(
-                notification.add(
-                    'error',
-                    'This web browser does not support Web Bluetooth or it is not enabled.',
-                    'https://github.com/WebBluetoothCG/web-bluetooth/blob/master/implementation-status.md',
-                ),
-            );
-            return;
-        }
-        // TODO: check navigator.bluetooth.getAvailability()
-        dispatch(willConnect());
-        try {
-            device = await navigator.bluetooth.requestDevice({
-                filters: [{ services: [pybricksServiceUUID] }],
-                optionalServices: [bleNusServiceUUID],
-            });
-        } catch (err) {
-            if (
-                err instanceof DOMException &&
-                err.code === DOMException.NOT_FOUND_ERR
-            ) {
-                // this can happen if the use cancels the dialog
-                console.debug('User cancelled connect');
-            } else {
-                console.error(err);
-                dispatch(
-                    notification.add(
-                        'error',
-                        'Unexpected error, check developer console for details.',
-                    ),
-                );
-            }
-            dispatch(didDisconnect());
-            return;
-        }
-        if (device.gatt === undefined) {
-            dispatch(notification.add('error', 'Device does not support GATT.'));
-            dispatch(didDisconnect());
-            return;
-        }
-        device.addEventListener('gattserverdisconnected', () => {
-            device = undefined;
-            rxChar = undefined;
-            dispatch(didDisconnect());
-        });
-        const server = await device.gatt.connect();
-        try {
-            const service = await server.getPrimaryService(bleNusServiceUUID);
-            rxChar = polyfillBluetoothRemoteGATTCharacteristic(
-                await service.getCharacteristic(bleNusCharRXUUID),
-            );
-            const txChar = await service.getCharacteristic(bleNusCharTXUUID);
-            txChar.addEventListener('characteristicvaluechanged', () => {
-                if (!txChar.value) {
-                    return;
-                }
-                dispatch({ type: BLEDataActionType.ReceivedData, value: txChar.value });
-            });
-            await txChar.startNotifications();
-        } catch (err) {
-            console.error(err);
-            dispatch(notification.add('error', 'Getting nRF UART service failed.'));
-            device.gatt.disconnect();
-            return;
-        }
-        dispatch(didConnect());
-    };
+export function notify(value: DataView): BLEDataNotifyAction {
+    return { type: BLEDataActionType.Notify, value };
 }
 
-export function disconnect(): BLEThunkAction {
-    return async function (dispatch): Promise<void> {
-        dispatch(willDisconnect());
-        device?.gatt?.disconnect();
-    };
+/** Common type for low-level BLE data actions. */
+export type BLEDataAction = BLEDataWriteAction | BLEDataNotifyAction;
+
+/**
+ * High-level BLE actions.
+ */
+export enum BLEActionType {
+    Toggle = 'ble.action.toggle',
 }
 
-export function write(value: ArrayBuffer): BLEThunkAction {
-    return async function (): Promise<void> {
-        // TODO: do we need to dispatch any Action<>s here?
-        for (let i = 0; i < value.byteLength; i += bleNusMaxSize) {
-            await rxChar?.xWriteValueWithoutResponse(value.slice(i, i + bleNusMaxSize));
-        }
-    };
+export type BLEToggleAction = Action<BLEActionType.Toggle>;
+
+export function toggleBluetooth(): BLEToggleAction {
+    return { type: BLEActionType.Toggle };
 }
+
+/** Common type for high-level BLE actions */
+export type BLEAction = BLEToggleAction;
diff --git a/src/actions/hub.ts b/src/actions/hub.ts
index 49b28713..c541cfca 100644
--- a/src/actions/hub.ts
+++ b/src/actions/hub.ts
@@ -2,11 +2,6 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { Action } from 'redux';
-import { ThunkAction } from 'redux-thunk';
-import { getChecksum } from '../epics/hub';
-import { write } from './ble';
-
-export type HubThunkAction = ThunkAction<Promise<void>, {}, {}, HubRuntimeStatusAction>;
 
 export enum HubRuntimeStatusType {
     Disconnected = 'disconnected',
@@ -17,83 +12,76 @@ export enum HubRuntimeStatusType {
     Error = 'error',
 }
 
-export enum HubActionType {
+export enum HubMessageActionType {
     /**
-     * MicroPython runtime status changed.
+     * The hub has send a message indicating the MicroPython runtime status changed.
      */
-    RuntimeStatus = 'hub.runtime.status',
+    RuntimeStatus = 'hub.message.action.runtime.status',
     /**
      * The hub has sent a checksum.
      */
-    Checksum = 'hub.runtime.checksum',
+    Checksum = 'hub.message.action.runtime.checksum',
 }
 
-export interface HubRuntimeStatusAction extends Action<HubActionType.RuntimeStatus> {
+export interface HubRuntimeStatusMessageAction
+    extends Action<HubMessageActionType.RuntimeStatus> {
     readonly newStatus: HubRuntimeStatusType;
 }
 
-export interface HubChecksumAction extends Action<HubActionType.Checksum> {
-    readonly checksum: number;
-}
-
-export function updateStatus(newStatus: HubRuntimeStatusType): HubRuntimeStatusAction {
+export function updateStatus(
+    newStatus: HubRuntimeStatusType,
+): HubRuntimeStatusMessageAction {
     return {
-        type: HubActionType.RuntimeStatus,
+        type: HubMessageActionType.RuntimeStatus,
         newStatus,
     };
 }
 
-export function checksum(checksum: number): HubChecksumAction {
+export interface HubChecksumMessageAction
+    extends Action<HubMessageActionType.Checksum> {
+    readonly checksum: number;
+}
+
+export function checksum(checksum: number): HubChecksumMessageAction {
     return {
-        type: HubActionType.Checksum,
+        type: HubMessageActionType.Checksum,
         checksum,
     };
 }
 
-const downloadChunkSize = 100;
+/**
+ * Common type for low-level hub message actions.
+ */
+export type HubMessageAction = HubRuntimeStatusMessageAction | HubChecksumMessageAction;
 
-export function downloadAndRun(data: ArrayBuffer): HubThunkAction {
-    return async function (dispatch): Promise<void> {
-        // let everyone know the runtime is busy loading the program
-        dispatch(updateStatus(HubRuntimeStatusType.Loading));
-
-        // TODO: might need to flush checksum queue here
-
-        // first send payload size as big-endian 32-bit integer
-        const checksum = getChecksum();
-        const sizeBuf = new Uint8Array(4);
-        const sizeView = new DataView(sizeBuf.buffer);
-        sizeView.setUint32(0, data.byteLength, true);
-        await dispatch(write(sizeBuf));
-        // TODO: verify checksum
-        console.log(await checksum);
-
-        // Then send payload in 100 byte chunks waiting for checksum after
-        // each chunk
-        for (let i = 0; i < data.byteLength; i += downloadChunkSize) {
-            // need to subscribe to checksum before writing to prevent race condition
-            const checksum = getChecksum();
-            await dispatch(write(data.slice(i, i + downloadChunkSize)));
-            // TODO: verify checksum
-            console.log(await checksum);
-            // TODO: dispatch progress
-        }
-
-        // let everyone know the runtime is done loading the program
-        dispatch(updateStatus(HubRuntimeStatusType.Loaded));
-    };
+/**
+ * High-level hub actions.
+ */
+export enum HubActionType {
+    DownloadAndRun = 'hub.action.downloadAndRun',
+    Stop = 'hub.action.stop',
+    Repl = 'hub.action.repl',
 }
 
-// SPACE, SPACE, SPACE, SPACE
-const startReplCommand = new Uint8Array([0x20, 0x20, 0x20, 0x20]);
+export type HubDownloadAndRunAction = Action<HubActionType.DownloadAndRun>;
 
-export function startRepl(): HubThunkAction {
-    return write(startReplCommand);
+export function downloadAndRun(): HubDownloadAndRunAction {
+    return { type: HubActionType.DownloadAndRun };
 }
 
-// CTRL+C, CTRL+C, CTRL+D
-const stopCommand = new Uint8Array([0x03, 0x03, 0x04]);
+export type HubStopAction = Action<HubActionType.Stop>;
 
-export function stop(): HubThunkAction {
-    return write(stopCommand);
+export function stop(): HubStopAction {
+    return { type: HubActionType.Stop };
 }
+
+export type HubReplAction = Action<HubActionType.Repl>;
+
+export function repl(): HubReplAction {
+    return { type: HubActionType.Repl };
+}
+
+/**
+ * Common type for all high-level hub actions.
+ */
+export type HubAction = HubDownloadAndRunAction | HubStopAction | HubReplAction;
diff --git a/src/actions/index.ts b/src/actions/index.ts
index 82e55208..3edb50f4 100644
--- a/src/actions/index.ts
+++ b/src/actions/index.ts
@@ -1,4 +1,5 @@
 import { Dispatch as ReduxDispatch } from 'redux';
+import { BLEAction, BLEConnectAction, BLEDataAction } from './ble';
 import {
     BootloaderAction,
     BootloaderConnectionAction,
@@ -7,6 +8,7 @@ import {
     BootloaderResponseAction,
 } from './bootloader';
 import { EditorAction } from './editor';
+import { HubAction, HubMessageAction } from './hub';
 import { NotificationAction } from './notification';
 import { ServiceWorkerAction } from './service-worker';
 import { TerminalDataAction } from './terminal';
@@ -15,12 +17,17 @@ import { TerminalDataAction } from './terminal';
  * Common type for all actions.
  */
 export type Action =
+    | BLEConnectAction
+    | BLEDataAction
+    | BLEAction
     | BootloaderConnectionAction
     | BootloaderRequestAction
     | BootloaderDidRequestAction
     | BootloaderResponseAction
     | BootloaderAction
     | EditorAction
+    | HubMessageAction
+    | HubAction
     | NotificationAction
     | ServiceWorkerAction
     | TerminalDataAction;
diff --git a/src/components/ActionButton.tsx b/src/components/ActionButton.tsx
index 39904db5..838f65ec 100644
--- a/src/components/ActionButton.tsx
+++ b/src/components/ActionButton.tsx
@@ -7,7 +7,7 @@ import Image from 'react-bootstrap/Image';
 import OverlayTrigger from 'react-bootstrap/OverlayTrigger';
 import Tooltip from 'react-bootstrap/Tooltip';
 
-export interface ActionButtonProps<T = undefined> {
+export interface ActionButtonProps {
     /** A unique id for each instance. */
     readonly id: string;
     /** Tooltip text that appears when hovering over the button. */
@@ -16,13 +16,11 @@ export interface ActionButtonProps<T = undefined> {
     readonly icon: string;
     /** When true or undefined, the button is enabled. */
     readonly enabled?: boolean;
-    /** Optional action hint passed to the onAction() callback. */
-    readonly context?: T;
     /** Callback that is called when the button is activated (clicked). */
-    readonly onAction: (context?: T) => void;
+    readonly onAction: () => void;
 }
 
-class ActionButton<T = undefined> extends React.Component<ActionButtonProps<T>> {
+class ActionButton extends React.Component<ActionButtonProps> {
     render(): JSX.Element {
         return (
             <OverlayTrigger
@@ -35,7 +33,7 @@ class ActionButton<T = undefined> extends React.Component<ActionButtonProps<T>>
             >
                 <Button
                     variant="light"
-                    onClick={(): void => this.props.onAction(this.props.context)}
+                    onClick={(): void => this.props.onAction()}
                     disabled={this.props.enabled === false}
                     style={
                         this.props.enabled === false
diff --git a/src/components/BluetoothButton.tsx b/src/components/BluetoothButton.tsx
index b3ba08e1..9397275e 100644
--- a/src/components/BluetoothButton.tsx
+++ b/src/components/BluetoothButton.tsx
@@ -2,9 +2,8 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { connect } from 'react-redux';
-import { AnyAction } from 'redux';
-import { ThunkDispatch } from 'redux-thunk';
-import { connect as bleConnect, disconnect as bleDisconnect } from '../actions/ble';
+import { Action, Dispatch } from '../actions';
+import { toggleBluetooth } from '../actions/ble';
 import { RootState } from '../reducers';
 import { BLEConnectionState } from '../reducers/ble';
 import { BootloaderConnectionState } from '../reducers/bootloader';
@@ -12,11 +11,8 @@ import ActionButton, { ActionButtonProps } from './ActionButton';
 import btConnectedIcon from './images/bt-connected.svg';
 import btDisconnectedIcon from './images/bt-disconnected.svg';
 
-type Dispatch = ThunkDispatch<{}, {}, AnyAction>;
-
-type ButtonProps = ActionButtonProps<string>;
-type StateProps = Pick<ButtonProps, 'tooltip' | 'icon' | 'context' | 'enabled'>;
-type DispatchProps = Pick<ButtonProps, 'onAction'>;
+type StateProps = Pick<ActionButtonProps, 'tooltip' | 'icon' | 'enabled'>;
+type DispatchProps = Pick<ActionButtonProps, 'onAction'>;
 
 const mapStateToProps = (state: RootState): StateProps => {
     if (
@@ -26,27 +22,19 @@ const mapStateToProps = (state: RootState): StateProps => {
         return {
             tooltip: 'Connect using Bluetooth',
             icon: btDisconnectedIcon,
-            context: 'connect',
             enabled: true,
         };
     } else {
         return {
             tooltip: 'Disconnect Bluetooth',
             icon: btConnectedIcon,
-            context: 'disconnect',
             enabled: state.ble.connection === BLEConnectionState.Connected,
         };
     }
 };
 
 const mapDispatchToProps = (dispatch: Dispatch): DispatchProps => ({
-    onAction: (c): void => {
-        if (c === 'connect') {
-            dispatch(bleConnect());
-        } else {
-            dispatch(bleDisconnect());
-        }
-    },
+    onAction: (): Action => dispatch(toggleBluetooth()),
 });
 
 export default connect(mapStateToProps, mapDispatchToProps)(ActionButton);
diff --git a/src/components/ReplButton.tsx b/src/components/ReplButton.tsx
index c890c929..eafe63bc 100644
--- a/src/components/ReplButton.tsx
+++ b/src/components/ReplButton.tsx
@@ -2,17 +2,14 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { connect } from 'react-redux';
-import { AnyAction } from 'redux';
-import { ThunkDispatch } from 'redux-thunk';
-import { startRepl } from '../actions/hub';
+import { Action, Dispatch } from '../actions';
+import { repl } from '../actions/hub';
 import { RootState } from '../reducers';
 import { HubRuntimeState } from '../reducers/hub';
 import ActionButton, { ActionButtonProps } from './ActionButton';
 import replIcon from './images/repl.svg';
 
-type Dispatch = ThunkDispatch<{}, {}, AnyAction>;
-
-type StateProps = Pick<ActionButtonProps, 'enabled' | 'context'>;
+type StateProps = Pick<ActionButtonProps, 'enabled'>;
 type DispatchProps = Pick<ActionButtonProps, 'onAction'>;
 type OwnProps = Pick<ActionButtonProps, 'id'>;
 
@@ -23,9 +20,7 @@ const mapStateToProps = (state: RootState): StateProps => ({
 });
 
 const mapDispatchToProps = (dispatch: Dispatch): DispatchProps => ({
-    onAction: (): void => {
-        dispatch(startRepl());
-    },
+    onAction: (): Action => dispatch(repl()),
 });
 
 const mergeProps = (
diff --git a/src/components/RunButton.tsx b/src/components/RunButton.tsx
index 05ee833e..dd2e5428 100644
--- a/src/components/RunButton.tsx
+++ b/src/components/RunButton.tsx
@@ -1,59 +1,32 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
-import { Ace } from 'ace-builds';
 import { connect } from 'react-redux';
-import { AnyAction } from 'redux';
-import { ThunkDispatch } from 'redux-thunk';
+import { Action, Dispatch } from '../actions';
 import { downloadAndRun } from '../actions/hub';
-import { compile } from '../actions/mpy';
-import * as notification from '../actions/notification';
 import { RootState } from '../reducers';
 import { HubRuntimeState } from '../reducers/hub';
 import ActionButton, { ActionButtonProps } from './ActionButton';
 import runIcon from './images/run.svg';
 
-type Dispatch = ThunkDispatch<{}, {}, AnyAction>;
-
-type ButtonProps = ActionButtonProps<Ace.EditSession>;
-type StateProps = Pick<ButtonProps, 'enabled' | 'context'>;
-type DispatchProps = Pick<ButtonProps, 'onAction'>;
-type OwnProps = Pick<ButtonProps, 'id'>;
+type StateProps = Pick<ActionButtonProps, 'enabled'>;
+type DispatchProps = Pick<ActionButtonProps, 'onAction'>;
+type OwnProps = Pick<ActionButtonProps, 'id'>;
 
 const mapStateToProps = (state: RootState): StateProps => ({
     enabled:
         state.editor.current !== null && state.hub.runtime === HubRuntimeState.Idle,
-    context: state.editor.current || undefined,
 });
 
 const mapDispatchToProps = (dispatch: Dispatch): DispatchProps => ({
-    onAction: (c): void => {
-        if (!c) {
-            console.error('No current editor');
-            return;
-        }
-        const script = c.getValue();
-        // TODO: need to get options from hub because they depend on firmware compile options
-        dispatch(compile(script, ['-mno-unicode']))
-            .then((mpy) => {
-                if (mpy.data) {
-                    dispatch(downloadAndRun(mpy.data));
-                } else {
-                    dispatch(
-                        notification.add('error', mpy.err || 'Unknown compiler error.'),
-                    );
-                }
-            })
-            .catch((err) => console.error(err));
-    },
+    onAction: (): Action => dispatch(downloadAndRun()),
 });
 
 const mergeProps = (
     stateProps: StateProps,
     dispatchProps: DispatchProps,
     ownProps: OwnProps,
-): ButtonProps => ({
-    tooltip: 'Download and run this program',
+): ActionButtonProps => ({
     icon: runIcon,
     ...ownProps,
     ...stateProps,
diff --git a/src/components/SaveAsButton.tsx b/src/components/SaveAsButton.tsx
index 4444e643..a0a3c32e 100644
--- a/src/components/SaveAsButton.tsx
+++ b/src/components/SaveAsButton.tsx
@@ -8,7 +8,7 @@ import { RootState } from '../reducers';
 import ActionButton, { ActionButtonProps } from './ActionButton';
 import downloadIcon from './images/download.svg';
 
-type StateProps = Pick<ActionButtonProps, 'enabled' | 'context'>;
+type StateProps = Pick<ActionButtonProps, 'enabled'>;
 type DispatchProps = Pick<ActionButtonProps, 'onAction'>;
 type OwnProps = Pick<ActionButtonProps, 'id'>;
 
diff --git a/src/components/StopButton.tsx b/src/components/StopButton.tsx
index a62fe3d6..de1653c0 100644
--- a/src/components/StopButton.tsx
+++ b/src/components/StopButton.tsx
@@ -2,17 +2,14 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { connect } from 'react-redux';
-import { AnyAction } from 'redux';
-import { ThunkDispatch } from 'redux-thunk';
+import { Action, Dispatch } from '../actions';
 import { stop } from '../actions/hub';
 import { RootState } from '../reducers';
 import { HubRuntimeState } from '../reducers/hub';
 import ActionButton, { ActionButtonProps } from './ActionButton';
 import stopIcon from './images/stop.svg';
 
-type Dispatch = ThunkDispatch<{}, {}, AnyAction>;
-
-type StateProps = Pick<ActionButtonProps, 'enabled' | 'context'>;
+type StateProps = Pick<ActionButtonProps, 'enabled'>;
 type DispatchProps = Pick<ActionButtonProps, 'onAction'>;
 type OwnProps = Pick<ActionButtonProps, 'id'>;
 
@@ -21,9 +18,7 @@ const mapStateToProps = (state: RootState): StateProps => ({
 });
 
 const mapDispatchToProps = (dispatch: Dispatch): DispatchProps => ({
-    onAction: (): void => {
-        dispatch(stop());
-    },
+    onAction: (): Action => dispatch(stop()),
 });
 
 const mergeProps = (
diff --git a/src/epics/ble.ts b/src/epics/ble.ts
index 9ba7c9fd..a613588a 100644
--- a/src/epics/ble.ts
+++ b/src/epics/ble.ts
@@ -26,7 +26,7 @@ const disconnect: Epic = (action$) =>
 
 const rxUartData: Epic<AnyAction, AnyAction, RootState> = (action$, state$) =>
     action$.pipe(
-        ofType<AnyAction, BLEDataAction>(BLEDataActionType.ReceivedData),
+        ofType<AnyAction, BLEDataAction>(BLEDataActionType.Notify),
         map((a) => {
             if (
                 state$.value.hub.runtime === HubRuntimeState.Loading &&
diff --git a/src/epics/hub.ts b/src/epics/hub.ts
index acb492c7..758d2928 100644
--- a/src/epics/hub.ts
+++ b/src/epics/hub.ts
@@ -5,13 +5,13 @@ import { AnyAction } from 'redux';
 import { Epic, combineEpics, ofType } from 'redux-observable';
 import { Subject } from 'rxjs';
 import { ignoreElements, take, tap } from 'rxjs/operators';
-import { HubActionType, HubChecksumAction } from '../actions/hub';
+import { HubChecksumMessageAction, HubMessageActionType } from '../actions/hub';
 
 const checksumSubject = new Subject<number>();
 
 const checksum: Epic = (action$) =>
     action$.pipe(
-        ofType<AnyAction, HubChecksumAction>(HubActionType.Checksum),
+        ofType<AnyAction, HubChecksumMessageAction>(HubMessageActionType.Checksum),
         tap((a) => checksumSubject.next(a.checksum)),
         ignoreElements(),
     );
diff --git a/src/reducers/ble.ts b/src/reducers/ble.ts
index 45891d4c..a36b4c85 100644
--- a/src/reducers/ble.ts
+++ b/src/reducers/ble.ts
@@ -31,11 +31,11 @@ const connection: Reducer<BLEConnectionState> = (
     action,
 ) => {
     switch (action.type) {
-        case BLEConnectActionType.WillConnect:
+        case BLEConnectActionType.Connect:
             return BLEConnectionState.Connecting;
         case BLEConnectActionType.DidConnect:
             return BLEConnectionState.Connected;
-        case BLEConnectActionType.WillDisconnect:
+        case BLEConnectActionType.Disconnect:
             return BLEConnectionState.Disconnecting;
         case BLEConnectActionType.DidDisconnect:
             return BLEConnectionState.Disconnected;
diff --git a/src/reducers/hub.ts b/src/reducers/hub.ts
index 95fc0221..090d13d6 100644
--- a/src/reducers/hub.ts
+++ b/src/reducers/hub.ts
@@ -3,8 +3,8 @@
 
 import { Reducer, combineReducers } from 'redux';
 import {
-    HubActionType,
-    HubRuntimeStatusAction,
+    HubMessageActionType,
+    HubRuntimeStatusMessageAction,
     HubRuntimeStatusType,
 } from '../actions/hub';
 
@@ -38,12 +38,12 @@ export enum HubRuntimeState {
     Error = 'hub.runtime.error',
 }
 
-const runtime: Reducer<HubRuntimeState, HubRuntimeStatusAction> = (
+const runtime: Reducer<HubRuntimeState, HubRuntimeStatusMessageAction> = (
     state = HubRuntimeState.Disconnected,
     action,
 ) => {
     switch (action.type) {
-        case HubActionType.RuntimeStatus:
+        case HubMessageActionType.RuntimeStatus:
             switch (action.newStatus) {
                 case HubRuntimeStatusType.Disconnected:
                     return HubRuntimeState.Disconnected;
diff --git a/src/services/ble.ts b/src/services/ble.ts
new file mode 100644
index 00000000..e4a5ee5a
--- /dev/null
+++ b/src/services/ble.ts
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2020 The Pybricks Authors
+
+import { Action, Dispatch } from '../actions';
+import {
+    BLEActionType,
+    BLEConnectActionType,
+    BLEDataActionType,
+    connect as connectAction,
+    didConnect,
+    didDisconnect,
+    disconnect as disconnectAction,
+    notify,
+} from '../actions/ble';
+import * as notification from '../actions/notification';
+import { RootState } from '../reducers';
+import { BLEConnectionState } from '../reducers/ble';
+import {
+    PolyfillBluetoothRemoteGATTCharacteristic,
+    polyfillBluetoothRemoteGATTCharacteristic,
+} from '../utils/web-bluetooth';
+import { combineServices } from '.';
+
+const pybricksServiceUUID = 'c5f50001-8280-46da-89f4-6d8051e4aeef';
+
+// nRF UART service (Nus)
+const bleNusServiceUUID = '6e400001-b5a3-f393-e0a9-e50e24dcca9e';
+const bleNusCharRXUUID = '6e400002-b5a3-f393-e0a9-e50e24dcca9e';
+const bleNusCharTXUUID = '6e400003-b5a3-f393-e0a9-e50e24dcca9e';
+const bleNusMaxSize = 20;
+
+let device: BluetoothDevice | undefined;
+let rxChar: PolyfillBluetoothRemoteGATTCharacteristic | undefined;
+
+async function connect(action: Action, dispatch: Dispatch): Promise<void> {
+    if (action.type !== BLEConnectActionType.Connect) {
+        return;
+    }
+
+    if (device !== undefined) {
+        dispatch(notification.add('error', 'A device is already connected.'));
+        return;
+    }
+    if (navigator.bluetooth === undefined) {
+        dispatch(
+            notification.add(
+                'error',
+                'This web browser does not support Web Bluetooth or it is not enabled.',
+                'https://github.com/WebBluetoothCG/web-bluetooth/blob/master/implementation-status.md',
+            ),
+        );
+        return;
+    }
+    // TODO: check navigator.bluetooth.getAvailability()
+    try {
+        device = await navigator.bluetooth.requestDevice({
+            filters: [{ services: [pybricksServiceUUID] }],
+            optionalServices: [bleNusServiceUUID],
+        });
+    } catch (err) {
+        if (err instanceof DOMException && err.code === DOMException.NOT_FOUND_ERR) {
+            // this can happen if the use cancels the dialog
+            console.debug('User cancelled connect');
+        } else {
+            console.error(err);
+            dispatch(
+                notification.add(
+                    'error',
+                    'Unexpected error, check developer console for details.',
+                ),
+            );
+        }
+        dispatch(didDisconnect());
+        return;
+    }
+    if (device.gatt === undefined) {
+        dispatch(notification.add('error', 'Device does not support GATT.'));
+        dispatch(didDisconnect());
+        return;
+    }
+    device.addEventListener('gattserverdisconnected', () => {
+        device = undefined;
+        rxChar = undefined;
+        dispatch(didDisconnect());
+    });
+    const server = await device.gatt.connect();
+    try {
+        const service = await server.getPrimaryService(bleNusServiceUUID);
+        rxChar = polyfillBluetoothRemoteGATTCharacteristic(
+            await service.getCharacteristic(bleNusCharRXUUID),
+        );
+        const txChar = await service.getCharacteristic(bleNusCharTXUUID);
+        txChar.addEventListener('characteristicvaluechanged', () => {
+            if (!txChar.value) {
+                return;
+            }
+            dispatch(notify(txChar.value));
+        });
+        await txChar.startNotifications();
+    } catch (err) {
+        console.error(err);
+        dispatch(notification.add('error', 'Getting nRF UART service failed.'));
+        device.gatt.disconnect();
+        return;
+    }
+    dispatch(didConnect());
+}
+
+function disconnect(action: Action): void {
+    if (action.type !== BLEConnectActionType.Disconnect) {
+        return;
+    }
+    device?.gatt?.disconnect();
+}
+
+async function write(action: Action): Promise<void> {
+    if (action.type !== BLEDataActionType.Write) {
+        return;
+    }
+    const value = action.value.buffer;
+    for (let i = 0; i < value.byteLength; i += bleNusMaxSize) {
+        await rxChar?.xWriteValueWithoutResponse(value.slice(i, i + bleNusMaxSize));
+    }
+}
+
+function toggle(action: Action, dispatch: Dispatch, state: RootState): void {
+    if (action.type !== BLEActionType.Toggle) {
+        return;
+    }
+    switch (state.ble.connection) {
+        case BLEConnectionState.Connected:
+            dispatch(disconnectAction());
+            break;
+        case BLEConnectionState.Disconnected:
+            dispatch(connectAction());
+            break;
+    }
+}
+
+export default combineServices(connect, disconnect, write, toggle);
diff --git a/src/services/hub.ts b/src/services/hub.ts
new file mode 100644
index 00000000..6835a39f
--- /dev/null
+++ b/src/services/hub.ts
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2020 The Pybricks Authors
+
+import { AnyAction } from 'redux';
+import { ThunkDispatch } from 'redux-thunk';
+import { Action } from '../actions';
+import { write } from '../actions/ble';
+import { HubActionType, HubRuntimeStatusType, updateStatus } from '../actions/hub';
+import { compile } from '../actions/mpy';
+import { getChecksum } from '../epics/hub';
+import { RootState } from '../reducers';
+import { combineServices } from '.';
+
+// TODO: this file needs to be converted to a saga
+
+type Dispatch = ThunkDispatch<{}, {}, AnyAction>;
+
+const downloadChunkSize = 100;
+
+async function downloadAndRun(
+    action: Action,
+    dispatch: Dispatch,
+    state: RootState,
+): Promise<void> {
+    if (action.type !== HubActionType.DownloadAndRun) {
+        return;
+    }
+
+    const script = state.editor.current?.getValue();
+    // istanbul ignore next: it should not be possible to trigger this action without a current editor
+    if (script === undefined) {
+        console.log('no current editor');
+        return;
+    }
+    const mpy = await dispatch(compile(script, ['-mno-unicode']));
+    if (mpy.data === undefined) {
+        console.log(`failed to compile: ${mpy.err}`);
+        return;
+    }
+
+    // let everyone know the runtime is busy loading the program
+    dispatch(updateStatus(HubRuntimeStatusType.Loading));
+
+    // TODO: might need to flush checksum queue here
+
+    // first send payload size as big-endian 32-bit integer
+    const checksum = getChecksum();
+    const sizeBuf = new Uint8Array(4);
+    const sizeView = new DataView(sizeBuf.buffer);
+    sizeView.setUint32(0, mpy.data.byteLength, true);
+    await dispatch(write(sizeBuf));
+    // TODO: verify checksum
+    console.log(await checksum);
+
+    // Then send payload in 100 byte chunks waiting for checksum after
+    // each chunk
+    for (let i = 0; i < mpy.data.byteLength; i += downloadChunkSize) {
+        // need to subscribe to checksum before writing to prevent race condition
+        const checksum = getChecksum();
+        await dispatch(write(mpy.data.slice(i, i + downloadChunkSize)));
+        // TODO: verify checksum
+        console.log(await checksum);
+        // TODO: dispatch progress
+    }
+
+    // let everyone know the runtime is done loading the program
+    dispatch(updateStatus(HubRuntimeStatusType.Loaded));
+}
+
+// SPACE, SPACE, SPACE, SPACE
+const startReplCommand = new Uint8Array([0x20, 0x20, 0x20, 0x20]);
+
+function startRepl(action: Action, dispatch: Dispatch): void {
+    if (action.type !== HubActionType.Repl) {
+        return;
+    }
+    dispatch(write(startReplCommand));
+}
+
+// CTRL+C, CTRL+C, CTRL+D
+const stopCommand = new Uint8Array([0x03, 0x03, 0x04]);
+
+function stop(action: Action, dispatch: Dispatch): void {
+    if (action.type !== HubActionType.Stop) {
+        return;
+    }
+    dispatch(write(stopCommand));
+}
+
+export default combineServices(downloadAndRun, startRepl, stop);
diff --git a/src/services/index.ts b/src/services/index.ts
index 6272d44e..5e88dae2 100644
--- a/src/services/index.ts
+++ b/src/services/index.ts
@@ -4,9 +4,11 @@
 import { Middleware } from 'redux';
 import { Action, Dispatch } from '../actions';
 import { RootState } from '../reducers';
+import ble from './ble';
 import bootloader from './bootloader';
 import editor from './editor';
 import errorLog from './error-log';
+import hub from './hub';
 
 type Service = (
     action: Action,
@@ -37,7 +39,7 @@ export function combineServices(...services: Service[]): Service {
     };
 }
 
-const rootService = combineServices(bootloader, editor, errorLog);
+const rootService = combineServices(ble, bootloader, editor, errorLog, hub);
 
 const serviceMiddleware: Middleware = (store) => (next) => (action): unknown => {
     runService(rootService, action, store.dispatch, store.getState());