BSP Developer's Guide

5
Driver Guidelines
block are more important than those in the code body. They will help others to
study the design without having to read the code bodies.
Bottom-Up Implementation
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After planning the driver and laying out its skeleton of functions and data
structures, you are ready to implement and test.
Write the Code
Start with device initialization. Write the code to accept a device structure and
initialize it for use. Fill in the bodies to all the other low-level driver functions.
You could do a test compile to check that all the necessary routines are
declared. Examine the symbols in the object module to verify that only the
desired external routines are unresolved.
Test, Debug, Recompile
The usual test, fix, and recompile cycle. Personal preferences guide this phase.
Some code and test one routine at a time.
Work One Layer at a Time
Repeat the write, test, debug, recompile cycle for each layer of code. Thorough
testing of each layer gives confidence in the project. Trying to write all the code
at once can be unmanageable.
Performance Testing
Some set of benchmark tests should be used to verify that the device meets the
usual customers expectations. A wide SCSI device that can only deliver
5 MB/s net throughput is not going to please the customer very much. It might
be necessary for the engineer to write a complete performance benchmark test
as part of the overall project.
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5.6 Cache Considerations
The VxWorks cache library (cacheLib) was designed to hide architecture and
target details from the rest of the system and to provide mechanisms to maintain
cache coherency. Cache coherency means data in the cache must be in sync (or
coherent) with that in RAM.
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