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WRSSQ

Writes the current value of the Time Stamp Counter (TSC) to the specified destination operand.

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

This instruction is only available when the processor is operating in 64-bit mode. It SHALL NOT be used in compatibility mode or 32-bit protected mode.

The destination operand MUST be 64 bits wide. If a memory destination is used, it MUST be aligned to an 8-byte boundary to avoid potential performance penalties or alignment checks. Writing the TSC to a register (r64) is the preferred method to ensure atomicity of the read operation.