Trace unit for data processor which outputs address values as the difference between the address and a base address in a register

摘要

A data processor has a trace unit to trace the operations of the processor. The trace unit has reference address registers, which store base addresses. When the unit outputs an address, it compares the address with the values in the reference registers. It then outputs the address value as a value indicating one of the reference registers and the difference between the address value and the value in the selected reference register. The difference may be an arithmetic difference or may be all the bits which are different. The selected reference register may be the one which gives the smallest difference. If the difference between the address to be traced and the reference register is greater than a threshold, the address to be traced may be stored in one of the reference registers. A diagnostic apparatus receives the values and reconstructs the original address.