= IEEE 1394 bus programming = Back to [/wiki] == libraw1394 == Documentation: [[http://www.dennedy.org/libraw1394/introduction.html]][[BR]] Function reference: [[http://www.dennedy.org/libraw1394/functions.html]] == FAQ == '''What does the "raw1394_start_lock64" function that "initiates a 64-bit compare-swap lock transaction" actually do?''' It initiates a 64-bit compare-swap lock transaction as defined in IEEE 1212. :-) This is needed for atomic manipulations of registers. This transaction contains an "argument" and a "data" value. Both values and the targeted register are 64 bits wide. - If the argument matches the old value of the register, data gets written into the register. - Otherwise, the register remains unchanged. The old value of the register is returned in the transaction response. This kind of access is in other contexts also known as compare-exchange function. It allows a register to be consistently updated by multiple concurrent requesters.