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Open Kernel Labs Blog
January 07, 2008
Programming In Hand-coded Assembler is Alive and Well at OK.
One of the appeals of doing embedded software development is theopportunity to build software that is based on good design principles and then
to squeeze out every ounce of performance through a series of
optimization techniques.
Hand coding a program in assembler (ASM) is one of the most
challenging, yet rewarding approaches to optimizing a program. Using
this approach, a programmer writes code directly using a human-
readable notation of the target machine's architecture. This allows
them to make full use of the architecture's instructions and features,
perhaps more so than a C compiler. Many application developers
dismissed hand coding of assembly decades ago as processor and
compiler technology improved to the state where there was little
benefit in spending the time it takes to write in ASM.
So, why is it so important for OK? Well, even with today's compiler
technology, we find that we can still optimize our critical code paths
by writing them in ASM with a significant performance benefit. We
usually achieve between a two and four fold increase in performance
compared to the original implementation. For example, the open-wait
IPC call on ARM is 345 cycles in C, versus 198 cycles when hand-coded.
Not bad huh?
We focus this optimization effort for critical code paths in the OKL4
microkernel. These are important as they are invoked frequently by
applications and other RTOS code which contributes to the operating
system's overheads.
For an example, download our public source release and take a look at
the generic (ipc.cc) versus optimized IPC path (traps.spp).
Happy Hacking!
Posted by Daniel Potts on January 07 at 03:31 PM
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About Daniel Potts:
Dr. Daniel Potts, Director of Engineering at OK Labs, heads up the engineering team and oversees the development our products. Dan enjoys working closely with his team, and ensuring that they have everything they need to focus on producing high quality products. When not working, you'll find Dan at the beach or swimming laps at the pool.