With the stepwise integration of the Real-time Preemption Patches (RT-Preempt) into the Mainline Linux kernel and their support for architectures other than Intel and AMD, there are now a number of choices which board to use for a particular embedded real-time project running Mainline Linux. In order to select the appropriate processor and clock frequency, it would be desirable to have some generally applicable ranges of worst-case latencies that can be obtained using the various processor types and conditions.

We, therefore, determined the internal worst-case latency of PowerPC and ARM boards running Linux 2.6.20 and above patched with RT-Preempt. The PowerPC-board (Phytec phyCORE-MPC5200B) was running at 266 and 400 MHz, the ARM board (Phytec phyCORE-PXA270) was running at 266 and 520 MHz.

This article will provide the details of the various measurement set-ups, present the results and discuss them with respect to the design differences between PowerPC and ARM.

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