Abstract:
The invention provides a debugging method applicable for an embedded system. The system includes a processor, a main memory and a debugging interface. A debugging program is first provided in the main memory. A debugging interruption is subsequently triggered to cause the processor to read the debugging program from the main memory and execute the debugging program. After execution, an execution result of the debugging program is stored into the main memory. The execution result is read and output via the debugging interface for further analysis. Because the architecture does not require a scan chain of ITR  104,  the circuit requirement is reduced while performance is increased.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a debugging method, and particularly, to an accurate and efficient debugging method for a digital signal processor (DSP) development board. 
         [0003]    2. Description of the Related Art 
         [0004]      FIG. 1  shows the architecture of a conventional board platform  100 . Embedded cores such as MPU or DSP cores are typically used in a conventional embedded system. A hardware emulator platform such as board platform  100  of  FIG. 1  is typically utilized to trace bugs and estimate performance during core development. In the board platform  100 , a processor  110  operates at frequency PCLK, and a debugging interface  130  operates at frequency TCK. Instructions executed by the processor  110  are selected from one of two sources via a prefetch  106 . In normal mode, instructions sent from the instruction memory  122  are selected and passed to the processor  110 . In debugging mode, the debugging interface  130  fetches a debugging program via a JTAG interface using a scan chain. The debugging program is first buffered in an instruction transfer register (ITR)  104 , and then passed to the processor  110  by the prefetch  106 . The debugging interface  130  is typically coupled to a debugger  140  or an external computer host. Thus, operations of the processor  110 , including stop, step-by-step run, interruption point configuration, and memory accessibility can be fully controlled. Furthermore, a plurality of registers  112  implemented in the processor  110 , are externally accessible via the debugging interface  130  as well as the main memory  120 . 
         [0005]      FIG. 2  is a flowchart of a conventional debugging method. The left side represents operations of the processor  110  at the frequency PCLK. In step  200 , the board platform  100  is triggered by a trigger signal to enter a debugging mode. The processor  110  first stops the current normal operation, and waits until execution of all instructions queued in the pipelines  114  is complete. In step  202 , the processor  110  enters a recursive waiting state, to wait for a debugging instruction to be passed from the ITR  104 . On the other hand, when the board platform  100  enters the debugging mode in step  200 , the debugging interface  130  processes step  212  to send externally input debugging instructions to the ITR  104 . In step  214 , when a debugging instruction is filled in the ITR  104 , the debugging interface  130  delivers a ready signal to the processor  110 , causing the processor  110  to exit the waiting state in step  202  and proceed to step  204 . The debugging interface  130  subsequently processes step  216 , an empty loop, to wait for an execution successful signal. In step  204 , the processor  110  reads and executes the debugging instruction from the ITR  104 . During the empty loop, any instruction associated data or parameters available in the data transfer register (DTR)  102 , are read by the processor  110 . In step  206 , an execution successful signal is delivered when the processor  110  completes execution of the debugging instruction, and the debugging interface  130 , in response, exits the waiting loop of step  216 . Subsequently, in step  218 , the debugging interface  130  issues a clear signal to indicate the current debugging instruction execution cycle has concluded. The debugging interface  130  then returns to step  212 , to wait for the next debugging instruction to be sent from the debugging interface  130 . The processor  110  simultaneously returns to step  202  to wait for another debugging instruction when conclusion of execution cycle is confirmed in step  208 . 
         [0006]    Because the frequencies PCLK and TCK are not identical, both parties rely on the waiting loops for handshake synchronization. Steps  202  to  218  are referred to as a round, during which only one debugging instruction can be input and executed to process only a predetermined amount of data. If the debugger  140  wants to write massive data to the data memory  124 , a plurality of rounds are required to sequentially process the massive data, inefficiently consuming significant time and system resource. Thus, a debugging method for improving the efficiency is desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An exemplary debugging method is provided, applicable for an embedded system comprising a processor, a main memory and a debugging interface. First, a debugging program is provided in the main memory. A debugging interruption is triggered on precise time to cause the processor to execute the debugging program from the main memory. After execution, an execution result of the debugging program is stored in the main memory. The execution result is subsequently read and output via the debugging interface for further analysis. 
         [0008]    An access allowable flag is further delivered upon completion of storage of the execution result storage. The debugging interface reads the execution result from the main memory when receiving the access allowable flag. The debugging interface may further monitor a state register. When execution of the debugging program is complete, the access allowable flag is stored into the state register. Thus, in response, the debugging interface reads the execution result from the main memory. 
         [0009]    The debugging interruption may be triggered when the processor runs to a program counter. A shadow register may be used to temporarily backup processor register values, and the debugging program may copy contents of the shadow register to the main memory as a part of the execution result. 
         [0010]    When the debugging interface obtains the execution result, a conclusion signal is issued, and the processor restores register values from the shadow register upon receipt of the conclusion signal. A state register is used to store the conclusion signal. When the debugging program is concluded, the debugging interface stores the conclusion signal in the state register upon receipt of the execution result. The processor then restores the processor register values from the shadow register upon detection of the conclusion signal. 
         [0011]    The embedded system that implements the debugging method is coupled to the debugging interface conforming to the JTAG standard. Any other board platform such as a development board is also adoptable for the debugging method, where the development board is referred to as a simulation environment of an embedded system. The processor may be an ARM instruction processor, preferably a PACDSP. The main memory comprises an instruction memory storing instructions to be processed by the processor, and a data memory storing data associated with the instructions. The execution result is stored in the data memory while the debugging program is stored in the instruction memory. The debugging interruption may be issued by a device an externally coupled to the debugging interface when the program counter satisfies a predetermined condition, or when the embedded system is interrupted by an externally coupled device. A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  shows the architecture of a conventional board platform  100 ; 
           [0014]      FIG. 2  is a flowchart of a conventional debugging method; 
           [0015]      FIG. 3  shows an architecture of a processor  300 ; and 
           [0016]      FIG. 4  is a flowchart of an embodiment of a debugging method. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0018]      FIG. 3  shows architecture of a processor. The processor  300  may be a VLIW type, comprising both MPU and DSP capabilities utilizing distributed register file clusters, which also referred to as a PACDSP. The processor  300  may comprise a plurality of clusters  302  each has various function units such as Load/Store unit or Arithmetic unit. Each function unit may further be associated with a dedicated private register file (not shown). An arithmetic unit (AU)  306  is capable of processing simple mathematic operations, address calculation and program control. A program controller  310  controls the resource dispatch of processor  300 , assigning different types of instructions to corresponding function units. Instruction associated data are transferred to the function units via a data memory interface unit (DMIU). Instructions are sent via an instruction memory interface unit (IMIU). 
         [0019]      FIG. 4  is a flowchart of an embodiment of a debugging method, suitable for a board platform  100  using the processor  300 . Contrary to a conventional sequential scan chain, the embodiment provides a batch processing method for efficiently executing a massive number of debugging instructions. Specifically, a software debugging procedure, triggered by an interruption when necessary, is provided. The method requires less circuit area, and improves the debugging performance. Intentional trigger points for debugging interruption may be provided. When the processor  300  detects the trigger points during normal program execution, an interruption is issued to enter the debugging mode. 
         [0020]    In  FIG. 4 , the processor  300  and the debugging interface  130  individually operate at different frequencies PCLK and TCK, each processing different steps. In step  400 , the processor  300  jumps to an entry point of a debugging program when triggered by a debugging interruption. The program counter and register contents at the moment are simultaneously stored for backup. A typical processor  300  may have a shadow register (not shown) backing up the interrupted register contents for further restore. In step  402 , the debugging program is initialized to perform various routing tests. In the embodiment, the debugging program is stored in the instruction memory  122 , and passed to the processor  300  by a prefetch  106 . Contrary to the conventional scan chain using ITR  104 , the debugging program of the embodiment is massively transferred to the processor  300 , significantly increasing the efficiency and performance. Furthermore, the processor  300  is capable of simultaneously processing various types of instructions by various function units, thus the massive input of debugging instructions can take full advantage of the processor  300 . In step  404 , an execution result of the debugging program is stored in the main memory  120 . More specifically, the execution result is stored in the data memory  124  of the main memory  120  by the processor  300  over the DMIU. In step  406 , upon completion of the execution result storage, an access allowable flag is issued to notify the debugging interface  130  (or an external host) that an execution result is available and accessible in the data memory  124 . The access allowable flag may be represented by a state register with a specified value. For example, the debugging interface  130  recursively monitors the state register, and reacts immediately when the value of the register changes. In step  408 , the processor  300  enters a waiting loop to wait for a conclusion signal from the debugging interface  130  (or the external host) that indicates the conclusion of the debugging mode. In step  410 , when the conclusion signal is issued, the processor  300  returns to normal mode, and all the register contents are restored to the processor  300 . 
         [0021]    On the other hand, simultaneous to initialization of the debugging mode in step  400 , the debugging interface  130  enters a waiting state in step  412 , to wait for the execution result to be generated. When an access allowable flag is issued, the debugging interface  130  (or the external host) processes step  414  to read the execution result stored in the data memory  124  of main memory  120  via a direct path marked as JMIU in  FIG. 1 . When the execution result is fully output, a conclusion signal is issued in step  416 , directing the processor  300  to conclude the debugging mode. The debugging procedure thus completes. 
         [0022]    Because the processor  300  triggers the debugging mode by an interruption, the interruption point can be accurately assigned to a specific program counter. Before the debugging program begins, the processor  300  drains out previously queued instructions in the pipeline stages. Contrary to conventional round by round instruction execution, the embodiment executes a batch of instructions by triggering one interruption, wherein the debugging program is referred to as a compiled form of the batch of instructions. 
         [0023]    In order to trace bugs, observation of the register contents of processor  300  is essential. Thus, the debugging program may copy contents of the shadow register and the data registers to the memory as a part of the execution result. 
         [0024]    In some embodiments, the board platform  100  may be a development board coupled to an external host or a debugger  140  via a debugging interface  130 . The DTR  102  in the board platform  100  may also be used as a state register to indicate a status inside the board platform  100 . For example, the conclusion signal issued in step  416  may also be stored in the DTR  102 , thus the processor  300  keeps monitoring the DTR  102  after step  406  until the conclusion signal is detected, and exits the debugging mode after register contents are restored to the processor  300  from the shadow register. 
         [0025]    The processor  300  may be an ARM instruction set processor, particularly a PACDSP, however the invention is not limited thereto. The main memory  120  in  FIG. 1  may comprise instruction memory  122  and data memory  124 . The instruction memory  122  is dedicated for storage of executable instructions, such as the debugging program. The execution result is put in the data memory  124 . The debugging mode is not limited to being triggered by an interruption. The processor  300  may issue the debugging interruption when the program counter satisfies a predetermined condition during normal program execution, or forcibly may be interrupted by the debugger  140  or an externally coupled host. In summary, the embodiment shows a software based method that does not require a scan chain of ITR  104 , therefore, no more hardware modification is required, and the performance can be increased without extra cost. 
         [0026]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.