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To determine the highest priority level that contains ready-to-run tasks, the bitmap table is scanned until the first bit set in the lowest bit position is found using OS_PrioGetHighest(). The code for this function is shown in Listing 6-1.
L6-1(1)OS_PrioGetHighest() scans the table from OSPrioTbl[0] until a non-zero entry is found. The loop will always terminate because there will always be a non-zero entry in the table because of the idle task. L6-1
(2)Each time a zero entry is found, we move to the next table entry and increment “prio” by the width (in number of bits) of each entry. If each entry is 32-bits wide, “prio” is incremented by 32.
L6-1(3)Once the first non-zero entry is found, the number of “leading zeros” of that entry is simply added and we return the priority level back to the caller. Counting the number of zeros is a CPU-specific function so that if a particular CPU has a built-in CLZ instruction, it is up to the implementer of the CPU port to take advantage of this feature. If the CPU used does not provide that instruction, the functionality must be implemented in C.
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