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?

[debugall]

Pull down a 10k resistor，

but why is Serial Downloader mode ok

[igorpadykov · Accepted solution]

if processor is running some code jtag connection may fail,

for reliable jtag connection recommended "Serial Downloader mode".

Best regards
igor

[igorpadykov]

Hi debugall

for "total IR len" issue one can check if jtag_mode is grounded, as in i.MX6ULL EVK

schematic 

Design files, including hardware schematics, Gerbers, and OrCAD files

Best regards
igor