System and method for using TAP controllers

1. Field of the Invention

The present invention relates to integrated circuits, and more particularly, to using TAP controllers.

2. Background

Conventional computer systems typically include several functional components. These components may include a central processing unit (CPU), main memory, input/output (“I/O”) devices, and storage devices (for example, tape drives, disk drives etc.) (referred to herein as “storage device”)

In conventional systems, the main memory is coupled to the CPU via a system bus or a local memory bus. The main memory is used to provide the CPU access to data and/or program information that is stored in main memory at execution time. Typically, the main memory is composed of random access memory (RAM) circuits. A computer system with the CPU and main memory is often referred to as a host system.

The storage device is coupled to the host system via a storage device controller that handles complex details of interfacing the storage device(s) to the host system. Communications between the host system and the controller is usually provided using one of a variety of standard input/output (“I/O”) bus interfaces.

Storage controllers are coupled using various standards, for example, the fibre channel standard incorporated herein by reference in its entirety.

As bandwidth increases, host systems and storage devices must transfer data efficiently. Because of high demand, it is desirable that the internal register files of integrated circuits (also referred to as “chips”) used in (or as) storage controllers be accessed real-time without disrupting normal chip operation for de-bugging or any other purpose.

A standard, IEEE 11491.1 and 11491A was developed (referred to as the JTAG standard) for testing of integrated circuits after assembly onto a printed circuit board, incorporated herein by reference in its entirety. The JTAG standard provides for testing numerous integrated circuits on a board as well as the interconnection of those circuits to the printed conductors of the board. Testing is performed using pins associated with a test access port (“TAP”).

TAP controllers are used to access chip information at a tap controller clock (tclk). In traditional systems, all chip operations stop when a chip is debugged using the JTAG standard. This is commercially undesirable because engineers may want to access the internal registers of a chip while it is operational.

Therefore, there is a need for a method and system that allows dynamic access to a chip via a TAP port during normal chip operation.

In one aspect of the present invention, a method for dynamically writing to an internal register space of a chip using a test access port (“TAP”) controller without interfering with the normal operation of the chip is provided. The method includes, loading write instructions and address of the internal register where data is to be written; and gaining access through arbitration to the internal register space.

Data that is to be written is loaded into a data register in the TAP controller before being written in the internal register space and the write instructions are loaded into an instruction register of the TAP controller.

In another aspect of the present invention, a method for dynamically reading from an internal register space of a chip without interfering with the normal operation of the chip is provided. The method includes, loading an address of the internal register space from where data is to be read, to the data register; gaining access to the internal register; and transferring information to a register in the TAP controller.

In yet another aspect of the present invention, a system for accessing an internal register space of a chip without interfering with the normal operation of the chip is provided. The system includes, an instruction register in the TAP controller to which read and/or write instructions are written; and an arbitration module that receives an input from the TAP controller when the TAP controller needs to access the internal register space.

In yet another aspect of the present invention, a TAP controller for dynamically accessing an internal register space in a chip without interfering the normal operation of the chip is provided. The TAP controller includes, an instruction register in the TAP controller to which read and/or write instructions are written; and a data register where data is stored after the TAP controller reads it from the internal register space, and/or data that is to be written into the internal register is first written to the data register.

In one aspect of the present invention, debugging can be performed dynamically because the internal registers of a chip can be accessed without interrupting the normal operation of the entire chip. This provides flexibility in debugging chips while using the JTAG standard.

This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings.

The foregoing features and other features of the present invention will now be described with reference to the drawings of a preferred embodiment. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures:

FIGS. 1A and 1B are block diagrams of a controller, used according to one aspect of the present invention;

FIG. 2 is a block diagram of a TAP controller, according to one aspect of the present invention;

FIG. 3 shows a flow diagram of process steps for reading internal register space of a controller using a TAP controller, according to one aspect of the present invention; and

FIG. 4 shows a flow diagram of process steps for writing to internal register space of a controller using a TAP controller, according to one aspect of the present invention.

To facilitate an understanding of the preferred embodiment, the general architecture and operation of a controller will initially be described. The specific architecture and operation of the preferred embodiment will then be described with reference to the general architecture.

System 100 A of FIG. 1A is an example of a storage system controller, included (or coupled to) in a computer system. The host computer (not shown) and a storage device 115 communicate via port 113 . In an alternate embodiment (not shown), the storage device 115 is an external storage device, which is connected to the host computer via a data bus. Those skilled in the art will appreciate that various communication buses known in the art can be used to transfer data between the drive and the host system.

As shown in FIG. 1A , the system includes controller 101 , which is coupled to fibre channel ports 102 and 103 , buffer memory 114 and microprocessor 100 . Interface 116 serves to couple microprocessor bus 107 to microprocessor 100 . A read only memory (“ROM”) omitted from the drawing is used to store firmware code executed by microprocessor 100 .

Controller 101 can be an integrated circuit (IC) that comprises of various functional modules, which provide for the writing and reading of data stored on storage device 115 or to other devices through fibre channel ports 102 and 103 .

Microprocessor 100 is coupled to controller 101 via interface 116 to facilitate transfer of data, address, timing and control information. Buffer memory 114 is coupled to controller 101 via ports to facilitate transfer of data, timing and address information.

Data flow controller 117 is connected to microprocessor bus 107 and to buffer controller 118 .

Disk formatter 110 formats data that is flowing through system 100 A, either from storage device 115 or from fibre channel ports 102 / 103 .

Fibre channel controllers 104 and 108 include programmable registers and state machine sequencers that interface with ports 102 and 103 . The fibre channel controllers 104 and 108 provide fibre channel control for ports 102 and 103 .

Microcontrollers 105 and 106 allow customization of fibre channel sequences and control Fibre channel controllers 104 and 108 through a microcontroller interface module 123 ( FIG. 1B ).

ECC engine 111 provides error correction for system 100 A.

TAP controller 119 , described in more detail below, is used to dynamically access the internal registers (for read and/or write) of system 100 A, without interfering with the normal operation of system 100 A. This enhances the overall debugging capabilities of system 100 A. Information from TAP controller 119 is sent to TAP controller port 120 and can be accessed outside system 100 A.

FIG. 1B shows a simplified block diagram of system 100 A. System 100 A includes internal register space 121 that can accessed by various components, including TAP controller 119 (may also be referred to as TAP controller interface 119 ).

An arbitration module (“arbiter”) 122 receives requests from various modules including microprocessor interface 116 and microcontroller interface 123 to access internal registers 121 . Other components, for example, buffer controller 118 may also access the register space via arbiter 122 .

FIG. 2 shows a detailed diagram of TAP controller 119 , according to one aspect of the present invention. TAP controller 119 includes a TAP controller state machine (“TAP FSM) 207 that receives plural inputs, including a clock input (tck) 206 ; a reset input (trst) 205 that can reset TAP controller 119 ; and a mode select input (tms) 204 ; and input tdi 203 that allows loading of TAP controller 119 register bits. TAP controller 119 provides output (tdo) 202 that uses tclk 206 and is enabled using tdo_enable bit 201 .

TAP controller 119 also includes a Multiplexer 215 whose output 209 is sent to TAP FSM 207 .

In one aspect of the present invention, TAP controller 119 uses plural registers; including an instruction register 208 and data register 210 to dynamically access internal register space 121 while system 100 A is functional.

Instruction register 208 and data register 210 are used to access internal register space 121 . Internal registers 121 can be accessed from outside system 100 A using microprocessor interface 116 or Microcontroller interface 123 .

If system 100 A is not fully functional or goes to an unknown state, and if it is not able to recover, microprocessor interface 116 or microcontroller interface 123 are not be able to access registers 121 . In such a case, TAP controller 119 , which runs on tck clock 206 and has its own I/O pins can be used to access internal register space 121 . This solution uses very little of the total logic and functions of system 100 A.

Instruction from data register 210 can be loaded using TAP controller 119 . The other registers of TAP controller 119 can also be loaded this way. The bits in data register 210 are used to define a cycle type (read command). One bit determines if it is a Read (1) or Write (0) cycle, and the other bit determines if it is a Byte (1) access or Word (0) access. The address of the register to be accessed is loaded into data register 210 and the data to be written (during a Write operation) is also stored in data register 210 .

For a Read operation the returned data is stored in data register 210 , which is then shifted out through tdo output port 202 . To ensure the validity of the data, a Data ready signal (which indicates that the read Data is ready), is also stored and shifted out.

FIG. 3 shows a flow diagram of process steps for reading internal register space 121 using TAP controller 119 while system 100 A is operational, according to one aspect of the present invention.

Turning in detail to FIG. 3 , in step S 300 , the address is loaded into data register 210 and the access width (for example, 8 bit or 16 bit) is loaded into instruction register 208 .

In step S 301 , a read command is loaded into instruction register 208 .

In step S 302 , a request is sent to arbiter 122 to gain access to internal register space 121 , as specified by the address.

In step S 303 , after the request is granted, data is moved to data register 210 and then shifted out in step S 304 , via tdo output 202 .

FIG. 4 shows a flow diagram of process steps for dynamically writing to internal register space 121 using TAP controller 119 while system 100 A is operational, according to one aspect of the present invention.

Turning in detail to step S 400 , the write address and data that needs to be written into internal register space 121 is loaded into data register 210 .

In step S 401 , a write command is loaded into instruction register 208 .

In step S 402 , a request to gain access to internal register space 121 is sent to arbiter 122 . Thereafter, in step S 403 , data is sent to internal register space 121 .

In one aspect of the present invention, debugging can be performed dynamically because the internal registers of a chip can be accessed without interrupting the normal operation of the entire chip. This provides flexibility in debugging chips while using the JTAG standard.

It is noteworthy that although the foregoing aspects have been described with respect to the JTAG standard, the adaptive aspects of the present invention are not limited to the JTAG standard. The foregoing process/system may be used to test any chip or integrated circuit, using any other standard.

Although the present invention has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present invention will be apparent in light of this disclosure.