Function

OSTestAndClear

Bit test and clear operation, performed atomically with respect to all devices that participate in the coherency architecture of the platform.

Declaration

Boolean OSTestAndClear(UInt32 bit, volatile UInt8 *startAddress);

Parameters

bit

The bit number in the range 0 through 7.

startAddress

The address of the byte to update atomically.

Return Value

true if the bit was already clear, false otherwise.

Discussion

The OSTestAndClear function clears a single bit in a byte at a specified address. It returns true if the bit was already clear, false otherwise.

This function guarantees atomicity only with main system memory. It is specifically unsuitable for use on noncacheable memory such as that in devices; this function cannot guarantee atomicity, for example, on memory mapped from a PCI device. Additionally, this function incorporates a memory barrier on systems with weakly-ordered memory architectures.