Anatomy of a Small Open-Source Kernel for DSPs

Julian provides the technical and historical background of dsp_k, with a particular focus on the kernel.
Deeply Embedded Open Source

I would now like to address how you might develop using the open-source model and what the open-source dsp_K license requires.

As proposed earlier, a hybrid development using both open- and closed-source software can work well, where the dsp_K software would form one open-source element. A vendor might provide you with a development board or reference design along with a port of dsp_K, which you might tailor and extend to suit your application. Mainly, this would simply involve modifying the dsp_Kcfg.h configuration file, but you might also write nonapplication-specific libraries or modify the kernel to exploit certain desirable features to fix bugs. You might choose to give modifications to the vendor for inclusion and support, remembering that in addition to your love for open-source engineering, money is made from products and services rather than the kernel.

Where do you start? First, you need to download the dsp_K software and documentation. Currently there exists a BSP only for the SHARC DSP, and furthermore this is integrated with the Visual DSP (VDSP) toolkit from Analog Devices, the company that makes these chips. In fact, there are old GNU tools for SHARC that you could try using (see Resources), and I'd love to hear your experiences if they work with dsp_K.

The second step is to try compiling the examples downloaded as part of the distribution. Using known-to-work software helps to establish confidence in your build environment. You might then try modifying one of the board-specific flashLED examples for your hardware. Once you have these running, you will be reasonably familiar with the software and can decide whether to continue using it for your project.

You are encouraged to modify the kernel to suit your own application needs. Indeed, you may well need to modify or extend the dsp_K software in order to provide required functionality on a particular target board or to extend or write a new API or device driver. The kernel must be capable of being built and run in various configurations, and as you add new kernel features, you can maintain confidence by performing regression tests. The generic source examples are a good way to do this, and you could write new ones to test your new features and libraries.

What if you choose to participate in the Open Source community by giving back your contributions? Or, what does the license require? First, read the license included with the downloaded distribution; it's not too long, and your obligations are lightweight. The dsp_K project allows you to choose the LGPL instead (see Resources), should you not wish to make use of the extra privileges afforded.

The extended privileges afforded by the dsp_K license aim to provide you and your business colleagues with a stepping stone, bridging the commercial world of deeply embedded systems with the Open Source community. The hybrid method described earlier captures this bridge practically. In fact, the LGPL probably allows similar privileges as our license, but this isn't made clear. The bottom line is that dsp_K is open source, and you must tell this to people to whom you distribute software based on it. Like you, they have the right to look at it and change it and the right to use a modified version with your (proprietary) application. You are neither obliged nor could you be reasonably compelled to give away your proprietary software.

Evolution

The version history of dsp_K is formally briefed in the document dsp_Ksrc.htm. Each major version represents a milestone in the kernel evolution.

Version 0.5.0 marked the first open-source release--on March 18, 2000, dspEK was announced on the comp.dsp newsgroup. The dspEK software continued to be minimally evolved and tested for subsequent 0.5 versions, but a new monolithic version, dspMK, was begun to create an open-source flavor of the proprietary dspOK and to include device drivers. Developments advanced modestly, and dspMK was released over the course of the following two months. Sharing a common core between dspEK and dspMK, the notion of APIs and the BSP as layers emerged. Consequently, the experimental tag became undesirable, so dspEK was deprecated by the short-lived but better named process flavor dspPK.

At the start of June 2000, the BSP and API layering had become clear, and the common kernel was folded into the project basename, dsp_K, creating version 0.6. While they persisted for a while, the API names dspPK and dspMK became process and monolith respectively. Seeking further development direction, integration with Linux and the Red Hat proposed EL/IX standard was identified as the basis for this work, which continues at this time, although at a modest pace, firmly establishing the software layer architecture with the BSP as a firm foundation.

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