imx6ull cannot jtag debugging in emmc startup mode

[debugall]

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?

[b36401]

You can use Serial Downloader mode as Igor suggested. For the details please refer to chapter 8.9 "Serial Downloader" of the Reference Manual.