imx6ull cannot jtag debugging in emmc startup mode,jtag show Device "MCIMX6Y2" selected. Connecting to target via JTAG ConfigTargetSettings() start J-Link script: Setting up AP map ConfigTargetSettings() end Could not measure total IR len. TDO is constant high. ConfigTargetSettings() start J-Link script: Setting up AP map ConfigTargetSettings() end Could not measure total IR len. TDO is constant high. ConfigTargetSettings() start J-Link script: Setting up AP map ConfigTargetSettings() end Could not measure total IR len. TDO is constant high. ConfigTargetSettings() start J-Link script: Setting up AP map ConfigTargetSettings() end Could not measure total IR len. TDO is constant high. Cannot connect to target. but Serial Downloader mode can jtag debug why?