The software used in the previous Elphel cameras was based on the GNU/Linux distribution supported By Axis Communications for their ETRAX processors. Of course it was heavily modified, we developed new code and ported many applications to run in the camera. Over the years we worked on making it easier to install, use and update, provided customized Live GNU/Linux distributions so those with zero experience with this operating system can still use the camera development software. Originally we used Knoppix-based CD, then DVD, then switched to Kubuntu when it became available and stable. And DVDs were eventually replaced by the USB flash drives.
Knoppix and Kubuntu are for the host computer, the cameras themselves used the same non-standard, mostly home-brewed distribution, that became more and more difficult to maintain especially when Axis abandoned their processors. So even during the first attempt to move to a new platform we really hoped to be able to use modern distribution for the embedded systems. And get rid of the nightmare of porting ourselves such applications as PHP and then doing mostly the same all over again when the new revisions became available. To be able to use the latest Linux kernel and not to spend time modifying the IDE driver myself to provide support for the large block hard drives when most manufacturers abandoned 512 byte ones – 2.6.19 kernel does not have it and there is not easy to use the later drivers.
Oleg is now working on adapting the OpenEmbedded distribution and the work flow for the new camera distribution, and while embracing the power of “bitbaking” we are trying to preserve the features we implemented in the NC353 camera software. And while the OpenEmbedded-based Yocto Project is for embedded system developers, we need the software for Elphel camera users – software that can be easily installed by a single script (at least on a particular GNU/Linux distribution) or come pre-installed on a flash media. It should work “out of the box” for the users with no prior GNU/Linux experience – most of the camera users have different OS on their computers. We would also like to keep what we believe has an important practical use – a feature behind our /*source is inside*/ logo on the cameras. Each camera keeps the source code of the modifications archived in the internal flash file system, so running the downloaded from the camera script by the user results in virtually identical binary image, even if some software in the camera was custom-modified from the official (supported through Elphel git repositories) distribution.
There is still a lot left in the OE that we do not fully understand, but we are trying to do it right from the very beginning, understanding how important it is from our experience of making some major re-organizing code for the previous products. And Oleg is doing a good progress, there is a wiki page and Git repositories: meta-elphel393, meta-ezynq that document our work on this.
I did not succumb to a temptation to start working on the FPGA code immediately – there are some new ideas we want to try as well as some left for a future major “revolution” when updating the existing cameras FPGA code for the new sensors and applications. Anyway – we are not under pressure to demonstrate images from the new camera and we are confident that this job will be done in the expected time and will have the NC393 operational by the second half of the 2014. And the time is working for us – there are many people working now with Xilinx Zynq, and the active development weeds out bugs at a high rate. Failing to upgrade to the latest version already took a whole week of development time – the bug in the Xilinx Ethernet driver turned out to be already fixed.
While Oleg was immersing himself into the OpenEmbedded I was looking into the kernel driver development, what changed since the 2.6.19 era I dealt with when working on the previous camera software. There turned out to be quite a few changes and I decided to learn the new features working on a simpler drivers that we needed for the new boards. First of all I was pleased to find out that of the 7 of the I²C chips used on the 10393+10389 boards 3 were supported by the available kernel drivers – had just to specify them in the Device Tree and the supercap-powered real time clock was immediately recognized by the system – so did the temperature sensor/EEPOM and GPIO ports. Of the remaining ones with no available drivers the most challenging turned out to be SI5338 (clock generator) and I tried to add support for this device, using sysfs to control it, Device Tree (DT) to initialize it, and dynamic debug to facilitate development – none of these interfaces were used in the previous cameras.
The SI5338 had all the needed documentation available on the manufacturer’s web site, ready for download. But the device itself turned out not to be to so easy to control, and the recommended procedure included generation of the register map with the ClockBuilder software (for MS Windows), then loading the data to the device registers and initializing it with rather simple code, for which Silicon Labs provides the source. That did not seem very convenient so I tried to implement the driver that can be controlled at run time directly, calculating the particular register values from the high-level data on the fly. Most features are now supported in the si5338.c driver, it is also possible to load the register data generated by the ClockBuilder software (it is possible to run it with Wine) after converting the file with the Python script. It took me more time than I expected to develop this driver to the usable state, but I hope this work will be useful for others too. SI5338 is an excellent device that deserves better support in the Linux kernel. And having the driver working – it eliminates the last remaining obstacle to start working on the FPGA code. Or one of the last remaining – there are still a few minor ones left.