A Faster Emulator with Better Hardware Support

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[This post is by Xavier Ducrohet and Reto Meier of the Android engineering team. — Tim Bray.]

The Android emulator is a key tool for Android developers in building and testing their apps. As the power and diversity of Android devices has grown quickly, it’s been hard for the emulator keep pace.

Today we’re thrilled to announce several significant improvements to the emulator, including a dramatic performance upgrade and support for a broader range of hardware features, notably sensors and multi-finger input.

Added GPU Support

The system image we’re shipping today has built-in GPU support (Android 4.0.3 r2). With Android’s growing reliance on using the GPU to improve performance, the difference is significant. In the video below, the emulator is still interpreting ARM instructions; the performance boost is the effect of putting the GPU to work.

As a bonus, since we’re now supporting OpenGL ES 2.0, your OpenGL games can now run inside the emulator.

Please note that there are a lot of GPUs out there, and we haven’t tested all of them for this beta release, so let us know if you have feedback or encounter issues.

More Hardware Feature Emulation

The hardware features of mobile devices are a significant part of what makes them a unique platform for development, so we’re also pleased to announce that in addition to the camera support we added last year, it’s now possible to use a tethered Android device to supply inputs for sensors and multi-touch input.

We’re working on providing emulator support for more hardware features including Bluetooth and NFC.

Improved CPU Performance

We’ve also improved the CPU performance of the Android emulator. Hardware floating point operation has been available for system images since Ice Cream Sandwich (Android 4.0), allowing CPU operations to be emulated roughly twice as quickly.

Last week’s r17 developer tools release included x86 system images and host drivers (available through the SDK Manager), allowing the emulator to access the host CPU natively and offer significantly faster execution.

This video shows a CPU-bound application on two emulators running the same system image, one with virtualization, one without.

Building a modern emulator

Because the Android platform allows deep interaction between applications, and with system components, we need to provide an emulator with a complete system image. Our emulator virtualizes a complete device: hardware, kernel, low-level system libraries, and app framework.

Of course, the system being emulated typically has an ARM CPU; historically, we’d been emulating those instructions in software, and that worked OK until the advent of tablet support with additional animations and complexity in Android 3.0.

The missing pieces were the completion of Android x86 support, and the GPU support in last week’s release of SDK Tools r17. This works by funneling the OpenGL ES 2.0 instructions from the emulator to the host OS, converted to standard OpenGL 2.0, and running natively on the host GPU.

Conclusion

The Android ecosystem has a lot of devices in many different form factors. Developers need a good way of testing these apps without having to own everything out there and a fast, rich Android emulator is immensely helpful.

We hope that these new improvements will make the emulator a more useful tool in your development and testing, and look forward to improving it further for you.

Activities and Tasks Design Guidelines

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For our third post in the series of Android UI, we're releasing Activity and Task Design Guidelines. This section of our guidelines aims to help you understand basic concepts of activities and tasks, how they work, and how to enrich the user experience you are creating.

We've packed a lot into this section, which is targeted at designers and developers. You'll see examples that will illustrate how to use our core principles and mechanisms, such as multitasking, activity reuse, intents, and the back stack.

Additionally, we are providing some best practices around our UI patterns such as notifications. For example, we'll show you how to design a notification so that it will take the user to the screen they expect. This behavior needs to be thought out, and doesn't necessarily just happen by default.

With helpful pointers to the API's and this documentation, we look forward to building your understanding of what it means to design and develop an Android UI.

A Little Too Popular

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A couple of weeks ago, we arranged that registered developers could buy an unlocked Nexus One via their publisher page in Android Market. We think it’s a good development platform and a nice phone. Apparently, you agree. Somewhat too many of you, in fact; we blew through the (substantial) initial inventory in almost no time, and they’re back-ordered from HTC, who are doing a pretty good job of managing runaway success amid a worldwide AMOLED shortage. Everyone appreciates that it’s important to the platform to get phones in the hands of developers, so we’re working hard on re-stocking the shelves; stand by.

A Bright Idea: Android Open Accessories

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[This post is by Justin Mattson, an Android Developer Advocate, and Erik Gilling, an engineer on the Android systems team. — Tim Bray]

Android’s USB port has in the past been curiously inaccessible to programmers. Last week at Google I/O we announced the Android Open Accessory APIs for Android. These APIs allow USB accessories to connect to Android devices running Android 3.1 or Android 2.3.4 without special licensing or fees. The new “accessory mode” does not require the Android device to support USB Host mode. This post will concentrate on accessory mode, but we also announced USB Host mode APIs for devices with hardware capable of supporting it.

To understand why having a USB port is not sufficient to support accessories let’s quickly look at how USB works. USB is an asymmetric protocol in that one participant acts as a USB Host and all other participants are USB Devices. In the PC world, a laptop or desktop acts as Host and your printer, mouse, webcam, etc., is the USB Device. The USB Host has two important tasks. The first is to be the bus master and control which device sends data at what times. The second key task is to provide power, since USB is a powered bus.

The problem with supporting accessories on Android in the traditional way is that relatively few devices support Host mode. Android’s answer is to turn the normal USB relationship on its head. In accessory mode the Android phone or tablet acts as the USB Device and the accessory acts as the USB Host. This means that the accessory is the bus master and provides power.

Establishing the Connection

Building an Open Accessory is simple as long as you include a USB host and can provide power to the Android device. The accessory needs to implement a simple handshake to establish a bi-directional connection with an app running on the Android device.

The handshake starts when the accessory detects that a device has been connected to it. The Android device will identify itself with the VID/PID that is appropriate based on the manufacturer and model of the device. The accessory then sends a control transaction to the Android device asking if it supports accessory mode.

Once the accessory confirms the Android device supports accessory mode, it sends a series of strings to the Android device using control transactions. These strings allow the Android device to identify compatible applications as well as provide a URL that Android will use if a suitable app is not found. Next the accessory sends a control transaction to the Android device telling it to enter accessory mode.

The Android device then drops off the bus and reappears with a new VID/PID combination. The new VID/PID corresponds to a device in accessory mode, which is Google’s VID 0x18D1, and PID 0x2D01 or 0x2D00. Once an appropriate application is started on the Android side, the accessory can now communicate with it using the first Bulk IN and Bulk OUT endpoints.

The protocol is easy to implement on your accessory. If you’re using the ADK or other USB Host Shield compatible Arduino you can use the AndroidAccessory library to implement the protocol. The ADK is one easy way to get started with accessory mode, but any accessory that has the required hardware and speaks the protocol described here and laid out in detail in the documentation can function as an Android Open Accessory.

Communicating with the Accessory

After the low-level USB connection is negotiated between the Android device and the accessory, control is handed over to an Android application. Any Android application can register to handle communication with any USB accessory. Here is how that would be declared in your AndroidManifest.xml:

Here's how you define the accessories the Activity supports:

The Android system signals that an accessory is available by issuing an Intent and then the user is presented with a dialog asking what application should be opened. The accessory-mode protocol allows the accessory to specify a URL to present to the user if no application is found which knows how communicate with it. This URL could point to an application in Android Market designed for use with the accessory.

After the application opens it uses the Android Open Accessory APIs in the SDK to communicate with the accessory. This allows the opening of a single FileInputStream and single FileOutputStream to send and receive arbitrary data. The protocol that the application and accessory use is then up to them to define.

Here’s some basic example code you could use to open streams connected to the accessory:

public class UsbAccessoryActivity extends Activity { private FileInputStream mInput; private FileOutputStream mOutput; private void openAccessory() { UsbManager manager = UsbManager.getInstance(this); UsbAccessory accessory = UsbManager.getAccessory(getIntent()); ParcelFileDescriptor fd = manager.openAccessory(accessory); if (fd != null) { mInput = new FileInputStream(fd); mOutput = new FileOutputStream(fd); } else { // Oh noes, the accessory didn’t open! } }}

Future Directions

There are a few ideas we have for the future. One issue we would like to address is the “power problem”. It’s a bit odd for something like a pedometer to provide power to your Nexus S while it’s downloading today’s walking data. We’re investigating ways that we could have the USB Host provide just the bus mastering capabilities, but not power. Storing and listening to music on a phone seems like a popular thing to do so naturally we’d like to support audio over USB. Finally, figuring out a way for phones to support common input devices would allow for users to be more productive. All of these features are exciting and we hope will be supported by a future version of Android.

Accessory mode opens up Android to a world of new possibilities filled with lots of new friends to talk to. We can’t wait to see what people come up with. The docs and samples are online; have at it!

[Android/USB graphic by Roman Nurik.]