Abstract: An apparatus and method for implementing watchpoints and breakpoints in a data processing system (110). In one embodiment, a pipelined processor (110) performs each instruction of a program. One or more watchpoints are associated with the instructions. The processor includes a history buffer (50) for storing processor state values at the time when each of the instructions was executed, until a predetermined time. Watchpoint information associated with a particular watchpoint is also stored in the history buffer (50), in association with the processor state values, such that the processor state is changed and the watchpoint is announced at the predetermined time. The watchpoint information may include increment/decrement information for one or more counters (41, 42). Breakpoint information may also be stored in history buffer (50).

Abstract: A master device (11) can access slave devices (12) either speculatively or non-speculatively. The slave devices (12) can be either non-hazardous devices or hazardous devices which exhibit status changes on reading. The master device (11) issues an access request including information as to whether the request is speculative or non-speculative, the slave device (12) then responds to the master device (11) with a negative acknowledgment that access is denied if the access request is speculative and the slave device (12) is hazardous. Otherwise, if the slave device (12) can deal with the request, a positive acknowledgment is sent. If the master device (11) receives a negative acknowledgment, it continues to reissue updated access requests until a positive acknowledgment is received.