AMD AMD-K6-2/500AFX Data Sheet - Page 180

AMD-K6®-2 Processor Data Sheet Preliminary Information 21850J/0-February 2000 Locked Operation with BOFF# Intervention Figure 70 shows BOFF# asserted within a locked read-write pair of bus cycles. In this example, the processor asserts LOCK# with ADS# to drive a locked memory read cycle followed by a locked memory write cycle. During the locked memory write cycle in this example, the processor samples BOFF# asserted. The processor immediately aborts the locked memory write cycle and floats all its bus-driving signals, including LOCK#. The system logic or another bus master can initiate an inquire cycle or drive a new bus cycle one clock edge after the clock edge on which BOFF# is sampled asserted. If the system logic drives a BOFF#-initiated inquire cycle and hits a modified line, the processor performs a writeback cycle before it restarts the locked cycle (the processor asserts LOCK# during the writeback cycle). In Figure 70, the processor immediately restarts the aborted locked write cycle by driving the bus off the clock edge on which BOFF# is sampled negated. The system logic must ensure the processor results for interrupted and uninterrupted locked cycles are consistent. That is, the system logic must guarantee the memory accessed by the processor is not modified during the time another bus master controls the bus. 160 Bus Cycles Chapter 5