API Changes

The most significant change from µC/OS-II to µC/OS-III occurs in the API. In order to port a µC/OS-II-based application to µC/OS-III, it is necessary to change the way services are invoked.

Table C-7 shows changes in the way critical sections in µC/OS-III are handled. Specifically, µC/OS-II defines macros to disable interrupts, and they are moved to µC/CPU withµC/OS-III since they are CPU specific functions.

Changes in macro naming
µC/OS-II (os_cpu.h)µC/CPU (cpu.h)
OS_ENTER_CRITICAL()CPU_CRITICAL_ENTER()
OS_EXIT_CRITICAL()CPU_CRITICAL_EXIT()


One of the biggest changes in the µC/OS-III API is its consistency. In fact, based on the function performed, it is possible to guess which arguments are needed, and in what order. For example, “*p_err” is a pointer to an error-returned variable. When present, “*p_err” is always the last argument of a function. In µC/OS-II, error-returned values are at times returned as a “*perr,” and at other times as the return value of the function. This inconsistency has been removed in µC/OS-III.

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