第八: JTAG。
按照电路图检查连接是否正确。
不能短路。否则可能出现全部一样的数值等现象（这也可能是配置文件错）。
PD脚的电压？如果没有，会说没有power等。
不能有过强干扰。看看tck_ret，如果衰减厉害，要接缓冲。看看gnd，要0V。
当用示波器看各个JTAG引脚时正确的情况是：
pd脚：
tck:对510一般是10.368mhz，560会相对快一些。
tck_ret:它是复制了tck信号，看衰减得厉害不。
tms：有新的调试操作实要改变状态的。
如果器件在run-test/idle状态时为低
如果器件在test logic reset 状态时为高
trst：低有效，在仿真的时候当然不能有效了。
下拉电阻，因为。。。
tdi:
tdo:
gnd:
emu0/1: 通常为高。
当调试时遇到中断，置低
当进行benchmarking,profiling,rtdx操作时，它用来传数据。
TRSTn:
Should be high during the test. Should pulse low between tests to toggle between test and emulation mode.
在reset时，仿真器会看pd是否有电，如果没有，他会拉高trst脚，然后对ccs说：can not detect power! 如果有电，它拉高trst脚后会马上再拉低它，表示正常。
TMS:
This signals is generally low but will pulse high at the beginning and end of each scan. Scan data is sent in either 8 or 16 bit blocks for most emulators. So you will see a burst of scan data then silence and the pattern will repeat.
TDO:
Emulator TDO, DSP TDI. You will see your scan pattern aligned with TMS.
TDI:
Emulator TDI, DSP TDO. You should see your scan pattern delayed by the length of the JTAG IR. All test scans are to the JTAG IR. At the end of a scan burst the DSP will tri-state the TDO pin. So you may see this pin slowly rise to a high level.
TCK/TCKRET:
Free running JTAG clock. Frequency is generally 10MHz when supplied by the emulator.
EMU0/1:
These signals are generally outputs from the DSP and do not change state.
下面是一些常见的TTAG问题：
1. Over 90% of scan related failures are a result of TCK/TCKRET signal. Always check this signal first. In many cases you may find that simply putting a scope probe on the TCK or TCKRET signal will make the diagnostics pass. This is clear indicator that TCK/TCKRET signals needs to be cleaned up or filtered. Testing has shown that on newer devices, DSP TCK is more noise sensitive then previous generations. Devices that fall into this class would be C64x, C55xx, OMAP, and custom ASIC devices. The predominant cause is related to type of input buffer being used on these devices and other signal coupling both on the board and in the DSP or package. In the majority of cases an AC terminator or small capacitor (12pf-33pf) at the DSP TCK pin will clear up the problem. In other cases you may need to buffer the TCK/TCKRET signals and terminate to resolve the problem.
clk不干净时，大多数情况下，在tck脚上接一个12到33pf的小电容即可。
2. The highest probability of emulator failure is the 14-pin JTAG connector. This is especially true in production test and programming environments where JTAG cable may be inserted and removes hundreds of times a day. If your 14-pin JTAG connector looks worn then run the diagnostics and twist/bend the JTAG cable near the connector. The TMS and TRSTn signals are generally the first signals to fail as the JTAG cable is generally “peeled” off the target versus being removed in a straight upward fashion.
tms和trst一般会是先阵亡的信号线。
注意用示波器看他们的波形是否正常。
3. If you are using a variable voltage emulator then first reset the emulator and probe the signals. Be sure that the PD pin on the JTAG connector is at the proper voltage level. Also, review the TCK/TCKRET for proper levels. In many emulators the TMS and TRSTn pins will be high following an emulator reset check these pins also.
pd的电压要和板子上的电源或io电压相同。
一般，reset后，tms和trest脚会出现一个高电平。
4. Most emulator design guidelines are out of date with respect to newer DSP devices and TCK/TCKRET noise. Routing a 4-6 inch TCK/TCKRET signals is not suggested for newer designs. Instead this distance should be limited to no more then 2 inches and the provision for an AC terminator should be include as a safety precaution. Also check with your emulator supplier to see if they have JTAG header adapters that include some form of buffering and termination.
5. Check with your silicon vendor as there may be known JTAG exceptions and special recommendations for the device you are using.
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LUS。