中文版本：
相信很多博友在调试ARM代码的时候，尤其是涉及到操作底层的时候，由于一些误操作常常会遇到Hard fault错误或者程序跑飞的情况，这些bug采用正常的方法是比较难定位的，往往需要我们逐行去排查测试，最后看的眼花缭乱，永远给人以苦逼程序员的印象，呵呵。此篇内容致力于节省广大程序员的精力，以崭新的一种方法角度或者说是手段来定位跟踪bug（仅限于支持Coresight技术的ARM处理器，本篇只讲针对M0+内核的），故冠之以“原创猛料”之称号，希望能名副其实，好了，闲话不多说，呵呵，开整……
ARM的Coresight技术估计大家有所耳闻（没听过的可以参考我之前的一篇介绍类文章http://blog.chinaaet.com/detail/29770.html），它实际上包括了ARM嵌入到其处理器内核的片上跟踪调试组件和相关的配套系统软件标准之类的，方便我们开发调试ARM产品。可能单说Coresight技术有点太泛了，把它具体化的话就不得不提到ETB（Embeded Trace Buffer）和MTB（Micro Trace Buffer）这两个经典的模块，其中ETB模块是Cortex-M3/M4内核的片上跟踪单元，而MTB模块则是Cortex-M0/M0+内核的跟踪单元。不过估计很多人没有用过，所以我就本着“吃螃蟹”的态度去尝试了一番，结果还是挺让我惊喜的，灰常好用，所以下面我就把使用方法分享给大家供大家评估，本文以MTB模块调试飞思卡尔基于Cortex-M0+内核的Kinetis L系列为例：
在介绍使用方法之前需要提一下，目前我测试的结果是J-link暂不支持MTB模块（但是支持ETB模块），所以我使用了OpenSDA平台的CMSIS-DAP固件来调用MTB模块，所以如果你手中有Kinetis L系列的Freedom板的话就直接可以跟我做了，其中CMSIS-DAP固件在本博客附件中，使用方法仍旧是类似更新OpenSDA的应用，不过换过CMSIS-DAP固件之后OpenSDA的小灯可能不亮，这个纯属正常，不要惊慌，哈哈。
测试环境：IAR6.6 + Freedom OpenSDA（CMSIS-DAP firmware）
测试目标芯片：Kinetis MKL25Z128
1）打开一个KL25的demo例程，然后右键工程Options->Debugger，选择“CMSIS-DAP”调试器，然后其他默认即可，设置完毕，点击“OK”，如下图所示：
2）点击调试按钮，进入调试界面，此时菜单栏会出现CMSIS-DAP选项，选择CMSIS-DAP->ETM Trace，调用MTB模块，弹出跟踪窗口，如下图所示。默认情况下跟踪功能是禁止的，此时点击跟踪窗口ETM Trace左上角的“电源符号”，打开跟踪功能，此时调试界面的左上角的ETM显示绿色，表示已经打开；
3）此时MTB功能已经打开，我们可以点击“全速运行”，然后再点击“暂停”，此时就可以在ETM Trace跟踪窗口看到从运行到断点停止这段时间所有的指令执行情况了，非常直观，如下图所示，此外可以选择同时查看汇编和C语言，也可以保存跟踪的结果，进而分析程序执行情况。
说到这，我们就该想到这种方式的好处了吧，如果遇到Hardfault或者程序跑飞的时候，通过设置断点或者点击暂停，然后就可以捕捉到出现hardfault或者程序跑飞的之前的程序执行情况从而帮助我们快速定位到bug的地方，非常方便实用。此外，实用CMSIS-DAP调试工具还有一个好处是，可以使用很多插件了，比如Timeline等等，灰常不错，哈哈~
English Version：
As we know, ARM Coresight, the ARM debug and trace technology, is the most complete on-chip debug and real-time trace solution for the entire System-On-Chip(SoC), making the ARM processor-based SoCs the easiest to debug and optimize. In this technology, the ETB in Cortex-M3/M4 and MTB in Cortex-M0/M0+ are representative two units, which can effectively help us to monitor the process of software executing or focus on some hard faults by tracing the instructions.
In the article, I wanna introduce the MTB useage in our product Kineits L series, which may be helpful to some customers using KL chip. But, before that, a CMSIS-DAP firmware for OpenSDA platform is needed, which you can find in the attachment of this article. So far as I know, it seems that J-Link don't support MTB yet, but do support ETB of Cortex-M4.
Testing Platform:
IAR EWARM6.6 + FRDM KL25 (OpenSDA with CMSIS-DAP fimware)
Testing steps:
1) firstly, update the OpenSDA with CMSIS-DAP fimware, just like other OpenSDA applications;
2) open any KL25 demo with IAR, access project setting "Options->Debugger", and select the "CMSIS-DAP" adapter as the screenshot shown below;
3) click the debug button to access thw debug window, then click the CMSIS-DAP->ETM Trace from the menu bar, and the ETM trace window will appear. Note that, the trace function is disabled in default, so another step is needed to click the "power port" at the top left corner to enable the trace function. The screenshot shows it below;
4) Now, the MTB is working. We can try it by click "run" and wait a while to click "pause", then the instructions from run to pause are shown in the trace window, it is really convenient. Besides, we can save, clear or zoom the trace results.
Conclution:
Through the above method, some painstaking issues like hardfault or program fleet can be captured simply by setting breakpoints or mannuly pause, which can help to positioning the source of the problem. Beyong that, the CMSIS-DAP can support plugs like timeline tool. BTW, it is a pity that MTB unit in the new Kinetis E series is cut out.
Happy Tracing!
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