Why Autotune failure Occured when I use cast drr command.

Hi,all

    the Test Env is  DS-5 and DSTREAM-ST and arm development board, When I execute csat.exe drr cmd , the error "Autotune failure. Please try to reboot target and select a lower frequency using the AutotuneMaxFreq config item." occured.

    I can't solve this error with cmd  "cfb JTAGAutoMaxFreq 2000" and "cfb JtagClockFreq 2000",

   so how can I solve this problem,Thanks!

%> cfb JTAGAutoMaxFreq 20000
Config item JTAGAutoMaxFreq was set to 20000
%> drr 0xff0
Reading from device no. 12: CSMEMAP_2
Failed to read register 0x00000ff0 for device no 12. Autotune failure. Please try to reboot target and select a lower frequency using the AutotuneMaxFreq config item.
Error: Failed to read register 4,080 on device CSMEMAP_2
%> cfb JtagClockFreq 2000
Config item JtagClockFreq was set to 2000

%> drr 0xff0
Reading from device no. 12: CSMEMAP_2
Failed to read register 0x00000ff0 for device no 12. Autotune failure. Please try to reboot target and select a lower frequency using the AutotuneMaxFreq config item.
Error: Failed to read register 4,080 on device CSMEMAP_2
%>

%> cfb JTAGAutoMaxFreq 2000
Config item JTAGAutoMaxFreq was set to 2000
%> drr 0xff0
Reading from device no. 12: CSMEMAP_2
Failed to read register 0x00000ff0 for device no 12. No connection to target.
Error: Failed to read register 4,080 on device CSMEMAP_2