本示例主要演示 CmBacktrace 软件包的自带的异常日志保存功能。该功能可以再系统发现异常的时，自动保存日志至异常日志分区，待下次重启后，自动恢复异常日志至文件中。方便开发者记录并分析上次出错的原因。
- 测试平台：潘多拉 IoT Board
- 依赖组件&软件包：DFS 、FAL
- 异常日志保存分区：位于片上 Flash 的
cmb_log分区 - 异常日志恢复文件路径：
/log/cmb.log，文件系统位于板载的 SPI Flash
将项目导入 RT-Thread Studio 或者打开 MDK5 工程，这里推荐使用 RT-Thread Studio 打开。
打开项目后，编译并下载程序至潘多拉开发板
检查启动日志，比如分区表信息。
启动成功后，在 MSH 命令行中新建 log 文件夹
msh />mkdir log 输入下面的命令，模拟触发 Hardfault 异常
msh />cmb_test DIVBYZERO重启开发板，可以看到如下类似如下日志：
[1116] I/cmb_log: An CmBacktrace log was found on flash. Now will backup it to file (/log/cmb.log).
[1149] I/cmb_log: Backup the CmBacktrace flash log to file (/log/cmb.log) successful.说明异常日志已经成功地恢复至文件中
使用 cat 即可查看异常文件内容
msh />cat log/cmb.log
[3082] E/cmb:
[3082] E/cmb: Firmware name: rtthread, hardware version: 1.0, software version: 1.0
[3082] E/cmb: Fault on thread tshell
[3082] E/cmb: ===== Thread stack information =====
[3082] E/cmb: addr: 20004198 data: 00000000
[3082] E/cmb: addr: 2000419c data: 00000000
[3082] E/cmb: addr: 200041a0 data: 00000000
[3082] E/cmb: addr: 200041a4 data: 00000000
[3082] E/cmb: addr: 200041a8 data: 00000000
[3082] E/cmb: addr: 200041ac data: 00000000
[3082] E/cmb: addr: 200041b0 data: 00000000
[3082] E/cmb: addr: 200041b4 data: 00000002
[3082] E/cmb: addr: 200041b8 data: 08016fb1
[3082] E/cmb: addr: 200041bc data: 00000008
[3082] E/cmb: addr: 200041c0 data: 200041c8
[3082] E/cmb: addr: 200041c4 data: 08006a95
[3082] E/cmb: addr: 200041c8 data: 00000012
[3082] E/cmb: addr: 200041cc data: 20003122
[3082] E/cmb: addr: 200041d0 data: 0801eef4
[3082] E/cmb: addr: 200041d4 data: 20003134
[3082] E/cmb: addr: 200041d8 data: 200041e0
[3082] E/cmb: addr: 200041dc data: 08007d81
[3082] E/cmb: addr: 200041e0 data: deadbeef
[3082] E/cmb: addr: 200041e4 data: 00000000
[3082] E/cmb: addr: 200041e8 data: deadbeef
[3082] E/cmb: addr: 200041ec data: 0000000d
[3082] E/cmb: addr: 200041f0 data: 200011e8
[3082] E/cmb: addr: 200041f4 data: 00000000
[3082] E/cmb: addr: 200041f8 data: 00000000
[3082] E/cmb: addr: 200041fc data: 00000003
[3082] E/cmb: addr: 20004200 data: deadbeef
[3082] E/cmb: addr: 20004204 data: deadbeef
[3082] E/cmb: addr: 20004208 data: deadbeef
[3082] E/cmb: addr: 2000420c data: 080038f9
[3082] E/cmb: addr: 20004210 data: 23232323
[3082] E/cmb: ====================================
[3082] E/cmb: =================== Registers information ====================
[3082] E/cmb: R0 : 00000000 R1 : 08022190 R2 : 0000000a R3 : 00000000
[3082] E/cmb: R12: 00000000 LR : 08016fdd PC : 08016ffa PSR: 61000000
[3082] E/cmb: ==============================================================
[3082] E/cmb: Usage fault is caused by Indicates a divide by zero has taken place (can be set only if DIV_0_TRP is set)
[3082] E/cmb: Show more call stack info by run: addr2line -e rtthread.elf -a -f 08016ffa 08016fd9 08016fad 08006a91 08007d7d 080038f5
[3082] E/cmb: Current system tick: 3082
msh />更多 CmBacktrace 软件包的使用说明，请查看其软件包介绍： http://packages.rt-thread.org/detail.html?package=CmBacktrace