LCA: Various topics from the mobile miniconf

The Serval project accounted for a number of separate talks at linux.conf.au 2013, but it was not the only project focused on free software in mobile computing. Among the others making a showing were OpenPhoenux, which is an ongoing effort to build and support new motherboards for the venerable OpenMoko Freerunner phone, and Mozilla's Firefox OS, whose team had demonstration hardware in tow. But there were also several talks that dealt with that most mainstream of mobile Linux platforms, Android, although in offbeat ways—such as deploying cutting-edge digital radio modes like codec2 on commodity mobile handsets.

OpenPhoenux

Often, new mobile platform projects (such as Jolla with Sailfish OS) spend a considerable amount of time searching for hardware partners interested in building devices, but the Open Pheonux project does just the opposite. It is plowing straight ahead at making its own phone motherboards, with interested hackers committing to pre-orders of small batches. The result of this approach is a more expensive per-unit price, but the hardware reaches the community quickly. Neil Brown presented a session explaining the goals of Open Phoenux and its current status, with hints at what may be coming in the next few months.

In its day, the Openmoko Freerunner was an exceptional device; the hardware was open in addition to the software. But the last motherboards produced by Openmoko were made in 2009; enthusiasts have subsequently been forced to look for old stock on eBay or other second-hand markets—and even when found, the 2009-era hardware shows its age. OpenPhoenux offers a brand new motherboard that fits into the same case as the original Freerunner, but sports a faster CPU (a 1GHz ARM Cortex-A8), more RAM (512MB), a 3G-capable modem, and an assortment of new or updated sensors (GPS, FM transceiver, accelerometer, compass, gyroscope, and altimeter). In addition, the various sensors and components have shrunk enough in size since 2009 that there is even more room today, so the new motherboard can overcome limitations in the original Freerunner design, like the lack of stereo speakers.

The OpenPhoenux motherboard is called the GTA04, and it is currently in revision 4 (denoted as GTA04A4). Brown said there are about 300 of the motherboards in the wild, and users are running a variety of software environments on them (including the Replicant Android distribution, QtMoko, and a derivative of the original GTK+-based Openmoko software), with several users using the GTA04 as their primary phone. Brown devotes most of his time to making sure that the mainline Linux kernel runs on the GTA04, which he described as a work in progress. There are a number of missing drivers at the moment, including the FM transceiver and the altimeter, and there are other sensors which are simply tricky to figure out how to support. For example, he said, what is an accelerometer? In some senses, it is used as an input device, responding to the user's movement, but at the same time, in produces a constant stream of sensor data whether the user is actively using it or not. As a result, there are two interfaces that need to be supported: that of a standard input device, and that of an Industrial IO (IIO) device. The kernel's IIO subsystem has recently moved out of staging and into main, he said, but it is still overly complex and not great to work with.

Keeping the kernel running is a constant challenge, Brown said, as there are always new bugs and old bugs reintroduced. He outlined a dozen or so from the period between kernel 3.5 to 3.7, such as CPU checks that incorrectly assume that cpu_is_omap34xx and cpu_is_omap3630 are mutually exclusive conditions—which they are not, as the GTA04 proves. There is also an ongoing struggle to minimize power consumption on the device, which Brown described as a nebulous challenge that touches many areas of the system at once and can be hard to track down. "If I see a green tinge on the screen, at least I know it is a problem with the video subsystem", he said. Still, it is a fun exercise, he said, and one that he learns from constantly. The next revision of the GTA04 boards (GTA04A5) is tentatively scheduled for March, if enough preorders are made by that time. The exact price depends on the number of orders, but is around the $500 range—there are plenty of cheaper alternatives, he cautioned: the OpenPhoenux's primary selling point is its complete openness. For now, that openness extends beyond the motherboard: users have recently started making their own alternative cases with 3d printers. In the future, some project members are looking for ways to add hardware keyboards, or to put the GTA04 into a tablet form factor with a bigger screen and battery.

Firefox OS and Android

On the subject of soon-to-be-available phone hardware, Mozilla developer Ben Kero presented a demonstration of Firefox OS running on the recently-announced developer phones at the mobile FOSS miniconf on Monday. Users have been able to run Firefox OS in a simulated environment through an add-on for quite some time, but seeing it running on actual devices is far more compelling. The developer phones are modest compared to a cutting edge Android device (the model on hand was the lower-end of the two, with a 1GHz processor), but thanks to the demo it is clear to see that Firefox OS is fast and responsive on them.

The developer phones are slated to be sold through Geekphone, a company that specializes in unlocked, hackable phone hardware, but two models is still not much of a selection. Several people in the audience expressed interest in what other hardware devices Firefox OS would be capable of running on. The good news is that Mozilla evidently tracks the official builds of the CyanogenMod project, and the Firefox OS build system automatically builds images for any device supported by CyanogenMod 9 or later. Firefox OS uses the kernel and hardware adaptation from CyanogenMod, Kero said, "we just tore out the Java". Perhaps predictably, a round of applause from the audience followed that comment.

Which is not to say that Android was a punching bag at the mobile computing talks at LCA 2013; there were in fact several talks that focused on Android specifically. But by and large, Android was seen as the commodity test platform on which other, more interesting work was based. Project Grimlock, for example, is a port of the Rhino JavaScript implementation to Android's Dalvik. Grimlock developer Maksim Lin also presented a session on modifying Android to run as an appliance-like operating system, like one might find in a kiosk or digital sign: a single application, presenting a stripped down interface to the user. As it turns out, running a kiosk-like appliance is relatively straightforward, once one knows where to look for the undocumented privileged APIs that Google apps routinely take advantage of. Lin said that many of the API calls are visible when reading through Android source, but that there are directives in the documentation that hide them whenever the documentation is rendered to HTML for display on a public web site. It was a thought-provoking talk that might make one seriously consider reading the Android source for the first time.

Codec2 and digital voice radio

Pushing boundaries was a common theme outside of the mobile FOSS miniconf as well. David Rowe presented his recent work on an extremely low-bitrate speech codec called codec2 which he has been developing for digital radio in the amateur-licensed HF and VHF bands. Codec2 can encode intelligible human speech in 1400 bits per second, which is a fraction of the bitrate required by analog voice modes in amateur radio. More importantly, it is significantly lower than the 2400 bits per second needed by comparable proprietary codecs. Digital voice modes in radio are a hot topic at the moment, and Rowe cautioned that if proprietary offerings were allowed to be blessed into standards, they would lock out open source, potentially for several decades to come.

The good news is that Rowe's work on codec2 does appear to be gaining traction with ham radio enthusiasts—and that, he said, bodes well for its future, because ham radio groups are influential with police, medical, and emergency services when the latter look to establish standards. At the moment, codec2 is usable immediately with Rowe's FreeDV, a cross-platform GUI application. Rowe demonstrated FreeDV and compared samples encoded with codec2 to other options. The FreeDV GUI is primarily used on Windows, he said, because most ham radio users are Windows-based, "but we are converting them over."

A ham radio codec might sound out of place at first, considering that ham radio is generally associated with hardware transceivers and fixed stations, but therein lies the secret. Following Rowe's talk was a demonstration by Joel Stanley, who showed codec2 running with software defined radio (SDR) on an Android handset. The combination of SDR and today's more powerful digital signal processors have the potential to blur the lines significantly between previously-distinct classes of communication, he said.

Stanley's demo was decidedly "homebrew" in appearance, but much of that stems from limits imposed by trying to create a device-vendor-neutral solution. He would have preferred to build a dongle that could plug directly into an Android phone's microphone port and receive HF radio, but that proved impossible because of the incompatible pinouts used by different phone makers. Instead, Stanley hooked the Android phone into a USB soundcard, but it did indeed serve as a working codec2 receiver. As was the case with the Serval project talks earlier in the event, it is intriguing to see free software used to redefine something so widespread (and taken for granted) as a mobile phone. It is a refreshing reminder that although Linux, through Android, has made enormous waves in the mobile industry, those waves do not stop at the edge of the app store.