Abstract: A processor (10) has a data cache unit (16) wherein the data cache unit includes a memory management unit (MMU) (32). The MMU contains memory locations within transparent translation registers (TTRs), an address translation cache (40), or a table walk controller (42) which store or generate cache mode (CM) bits which indicate whether a memory access (i.e., a write operation) is precise or imprecise. Precise operations require that a first write operation or bus write instruction be executed with no other operationsnstructions executing until the first operation/instruction completes with or without a fault. Imprecise operations are operations/instruction which may be queued, partially performed, or execution simultaneously with other instructions regardless of faults or bus write operations. By allowing the logical address to determine whether the bus write operation is precise or imprecise, a large amount of system flexibility is achieved.

Abstract: A scan chain architecture which has a controller (10), and a multiplexer (24) is used to route test data through functional units (12, 14, 16, 18, 20, and 22). The controller (10) receives as input a serial data stream from an STDI terminal and demultiplexes this data stream to one of the functional units (six functional units are illustrated in FIG. 1). Each of the functional units is considered as one scan chain and therefore FIG. 1 has six scan chains (one for each functional unit). In addition, a seventh scan chain couples all output flip-flops in each of the functional units together between an output of the MUX (24) and the STDO terminal/pin. Therefore, a serial scan of a data stream can be done through one functional unit, the multiplexer (24) and into the output flip-flops of each function unit to make testing easier to set-up. In addition, various new scan chain cells and low power methods are used herein.

Abstract: A processor (10) has two modes of operation. One mode of operation is a normal mode of operation wherein the processor (10) accesses user address space or supervisor address space to perform a predetermined function. The other mode of operation is referred to as a debug, test, or emulator mode of operation and is entered via an exception/interrupt. The debug mode is an alternate operational mode of the processor (10) which has a unique debug address space which executes instructions from the normal instruction set of the processor (10). Furthermore, the debug mode of operation does not adversely affect the state of the normal mode of operation while executing debug, test, and emulation commands at normal processor speed. The debug mode is totally non-destructive and non-obtrusive to the "suspended" normal mode of operation. While in debug mode, the existing processor pipelines, bus interface, etc. are utilized.