| 摘要 |
An apparatus and methods for data exchange with microcomputing devices. In one embodiment, the invention consists of a microcomputing device having a plurality of instruction buses. The first bus is the primary instruction bus from which the device core receive application instructions. A secondary bus is the bus from which the device core receives data exchange instructions. Operative with the plural instruction buses is circuitry for receiving data exchange instructions on the secondary instruction bus and circuitry for selecting from which of the instruction buses the core fetches instructions on any given cycle. In addition to plural instruction buses, some instructions specific to data exchange have been added to the core's instruction set, allowing the device to perform data exchange instructions such as read and write with a single-word data exchange instruction. A method for summoning the core to perform a data exchange subroutine without the use of interrupts is provided. In accordance with the method, upon completion of the data exchange subroutine, the device resumes execution of foreground tasks. Appropriate flags, able to be sensed and cleared by external means, are provided to indicate that a data exchange subroutine is in service or completed. A method for implementing hardware and software breakpoints is provided. Data exchange instructions are described that gain control of the core to allow foreground processes to be single-stepped, while allowing background processes to continue. Again, flags are provided to indicate breakpoint status and may be sensed and cleared by external means. Finally, a JTAG scan engine capable of data exchange and an array of such JTAG scan engines in a debug and test system for microcomputing devices is presented.
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