Current, more and more embedded the ICE emulator that development company and engineer begin to use JTAG means comes to those who have a program debug the job. Traditional whole emulation pattern (FullICE) is being used gradually the JTAG with agile, low cost emulates means place to replace.

JTAG emulator can be satisfied at present embedded all and main demand that the program debugs, for example: Breakpoint setting, single step tries, observation of memory editor, variable, register. (If pursue 1 is shown)

Breakpoint setting is JTAG emulator is the basiccest debug a function. The user needs a system to be in the reentry after stopping to be debugged all right in setting breakpoint. Breakpoint differs to divide the sort that differs for a few again according to principle and utility. The article introduces type of commonly used a few kinds of breakpoint will simply.

Breakpoint can divide for hardware breakpoint and software breakpoint two kinds big:

1. Hardware breakpoint needs the hardware support of target CPU, the design of ARM7/9 in-house hardware of current popularity offers two groups of register to use information of the breakpoint that put store, so ARM7/9 kernel supports two hardware breakpoint at most, and ARM11 can support 8 hardware breakpoint. This and debug implement have nothing to do.

2. Software breakpoint comes true through the pattern of eigenvalue is being set in code. When should needing to be in setting software breakpoint in some address code, emulator can have here code backing up protective first, next will beforehand the breakpoint eigenvalue with good set (wait to be worth promiscuously not easily with code for 0x0000 commonly) write here location, enclothe original code data. Move when the program come here when the address that eigenvalue is in, emulator identifying gives here is a soft breakpoint, can arise interrupt. When cancelling breakpoint, the code information that protection gets before can be restored automatically.

Hardware breakpoint can install the code in any positions to go up, include ROM and RAM; And because software breakpoint needs to revise the cost of corresponding address, can set on RAM only commonly so, but the amount need not accept restriction. As a result of the flexibility that hardware breakpoint installs, it is the most preferential so chosen breakpoint resource, but the need that two breakpoint often satisfy an engineer very hard to undertake be debugginged deep, the additional natural resources that then software breakpoint can regard hardware as breakpoint will use.

As a result of normally on the code that software breakpoint can establish in RAM to move only, and the code amount as the system is larger and larger, be in especially mobile domain, the RAM of augment high capacity will naturally raise the cost of the product, so a lot of systems move code on FlashROM directly now. The system of code runs on FlashROM to this kind, general software breakpoint cannot be installed, this also is the limitation of software breakpoint. To such system, can satisfy need through using two hardware breakpoint alternately only, but can bring certain inconvenience.
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