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Anchor10306111030611 Measuring Interrupt Disable Time Anchor10306121030612µC/CPU provides facilities to measure the amount of time interrupts are disabled. This is done by setting the configuration constant CPU_CFG_INT_DIS_MEAS_EN to 1 in cpu_cfg.h. anchor10306131030613

The measurement is started each time interrupts are disabled and ends when interrupts are re-enabled. The measurement keeps track of two values: a global interrupt disable time, and an interrupt disable time for each task. Therefore, it is possible to know how long a task disables interrupts, enabling the user to better optimize their code.anchor

10306141030614The per-task interrupt disable time is saved in the task’s OS_TCB during a context switch (see OSTaskSwHook() in os_cpu_c.c and described in Chapter 8Chapter 8, “Context Switching” on page 149). Anchor10306151030615

The unit of measure for the measured time is in CPU_TS (timestamp) units. It is necessary to find out the resolution of the timer used to measure these timestamps. For example, if the timer used for the timestamp is incremented at 1 MHz then the resolution of CPU_TS is 1 microsecond1 microsecond.

Anchor10306161030616Measuring the interrupt disable time obviously adds measurement artifacts and thus increases the amount of time the interrupts are disabled. However, as far as the measurement is concerned, measurement overhead is accounted for and the measured value represents the actual interrupt disable time as if the measurement was not present. Anchor10306171030617

Interrupt disable time is obviously greatly affected by the speed at which the processor accesses instructions and thus, the memory access speed. In this case, the hardware designer might have introduced wait states to memory accesses, which affects overall performance of the system. This may show up as unusually long interrupt disable times.