Monday, October 4, 2010

uCOS-III VS uCOS-II (Features)

Migrating from uCOS-II to uCOS-III was a humming question in my head and the heads of many. I started trying to answer this question with the idea that uCOS-III is totally a new kernel but with roots into uCOS-II. My survey is based on uCOS-II source code and the Win32 for uCOS-III evaluation I got recently.

Differences between uCOS-III and uCOS-II can be classified under 5 categories:
  1. Features
  2. Source file names and contents
  3. Conventions
  4. Variable names
  5. API changes
These areas are of great importance for those who are willing to port uCOS-II applications to uCOS-III.

I will try to explain briefly each category in a separate post.

If any of my results are not accurate enough due to the lackness of uCOS-III source code, please feel free to email me at to correct it in this post.

Changes in Features
uCOS-III is introduced in 2009 while uCOS-II was first introduced in 1998. For both kernels, books and source code are available. But for uCOS-III, Micrium followed a new model. The source code is made available only to licensed users.

Unlike uCOS-II, uCOS-III has no limitation on numbers of tasks (255 tasks mazimum in uCOS-II) nor on the number of tasks at each priority level. Consequently, RR scheduling was introduced in uCOS-III.

uCOS-III kept all services available except for the message mailbox. It was totally removed. Although a message mail box can be used exactly like a binary semaphore, in addition for message passing, but after all it is indeed a message queue with a single entry. Another breakthrough is that mutexes and task's suspension resumption now support nesting.

Advances in performance were considered in the design of uCOS-III compared to uCOS-II. Smaller code size, support for run-time configurability, less interrupt latency, enhanced built-in measurements, time stamping on posting APIs, optimize schedulers in assembly are dreams coming into reality.

uCOS-III is working on being a safety-critical certified software. It is compliant with
MISRA C 2004 (except for 8 rules) and the certificaion is in progress to achieve DO178B Level A, EUROCAE ED-12B, SIL3/SIL4, and IEC 61508.

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