The J-Link RDI software contains an add. feature, called Flash break points (short FlashBPs). This feature requires an add. license. It adds the ability to set an unlimited number of software breakpoints in flash memory areas, rather than just the 2 hardware breakpoints.

How do breakpoints work?

There are basically 2 types of breakpoints in a computer system: Hard ones and soft ones. Hard BPs require a dedicate hardware unit for every hardware breakpoint. In other words, the hardware dictates how many hardware breakpoints can be set simultaneously. ARM7 and ARM 9 cores have 2 breakpoint units (called "watchpoint units" in ARM's documentation), allowing 2 hardware breakpoints to be set. Hardware breakpoints do not require modification of the program code. Software breakpoints are different: The debugger modifies the program and replaces the breakpointed instruction with a special value. Add. soft BPs do not require add. hardware units in the processor, since simply more instructions are replaced. This is a standard procedure that most debuggers are capable of, however, it requires the program to be located in RAM.

What is special about software breakpoints in flash ?

It allows you to set an unlimited number of breakpoints even if your application program is not located in RAM, but in Flash memory. This is a scenario which was very rare before ARM-microcontrollers hit the market. This new technology makes very powerful, yet inexpensive ARM microcontrollers available for systems, which required external RAM before. The downside of this new technology is that it is not possible to debug larger programs on these Micros in RAM, since the RAM is not big enough to hold program and data (typically, these chips contain about 4 times as much flash as RAM), and therefore with standard debuggers, only 2 breakpoints can be set. The 2 breakpoint limit makes debugging very tough; a lot of times the debugger requires 2 breakpoints to simply step over a line of code. With software breakpoints in Flash, this limitation is gone.

How does this work ?

Basically very simple:
The J-Link RDI-software reprograms a sector of the flash to set or clear a breakpoint.

What performance can I expect ?

A RAM code, specially designed for this purpose, sets and clears Flash breakpoints extremely fast; on micros with fast flash the difference between breakpoints in RAM and Flash is hardly noticeable

How is this performance achieved ?

We have put a lot of effort in making FlashBPs really usable and convenient. Flash sectors are programmed only when necessary; this is usually the moment execution of the target program is started. A lot of times, more then one breakpoint is located in the same flash sector, which allows programming multiple breakpoints by programming just a single sector. The contents of program memory are cached, avoiding time consuming reading of the flash sectors. A smart combination of software and hardware breakpoints allows us to use hardware breakpoints a lot of times, especially when the debugger is source level-stepping, avoiding reprogramming of the flash in these situations. A built-in instruction set simulator further reduces the number of flash operations which need to be performed. This minimizes delays for the user, maximizing the life time of the flash. All resources of the ARM micro are available to the application program, no memory is lost for debugging. All of the optimizations described above can be disabled.

The feature is available for the following chips at this time:

More chips will be supported in the future.

Licensing

The software is licensed on a per J-Link basis. It requires a J-Link with RDI feature.
The following items are required to use software:

• J-Link
• RDI license
• Flash breakpoints license

In order to receive your free 30 days trial license, follow the steps on how to obtain and installing the license key.

Setting up flash breakpoints

Step 1
Download the RDI software.
Step 2
Unzip the files to a folder on your hard drive e.g. c:\Segger\JLinkRDI. Important: The IAR program folder (normally C:\Program Files\IAR Systems\Embedded Workbench 4.0\arm\bin) contains a version of JLinkARM.dll. Please overwrite this older version with the new version in the zip file.
Step 3
Start the IAR Embedded Workbench.
Step 4
Open the sample workspace for your CPU.
Step 5
Choose Project|Options from the Menu and the Options dialog box pops up. Browse to the JLinkRDI.dll and click OK.
Step 6
Choose RDI|Configure from the Menu and the RDI configuration dialog box appears on your screen. Click on the "Flash" tab.
Step 7
Select your your processor and flash address. Click on the "Breakpoints" tab.
Step 8
Configure the use of breakpoints as prefered. Click the OK button to close the RDI configuration dialog.
Step 9
Start the debugger.

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